Fraser Cain: We’re back in the swing of things. Last week we examined the largest wavelength in the electromagnetic spectrum – radio. This week we get a little smaller, but not too small and look at the next step in the spectrum – submillimeter.

Astronomers have only recently begun exploring this tiny slice of the spectrum. The path has already been huge. Where can we find the submillimeter wavelength?

Dr. Pamela Gay: When we talk about submillimeter astronomy we’re typically talking wavelengths that have a peak to peak distance of about point 3 millimeters out to about a few millimeters which aren’t necessarily submillimeter.

We’re confined in what we can look at by our atmosphere. If you ask me to find the geography of where we can observe submillimeter I’d say go up. Go up really high.

Fraser: Radio goes from meters down to a few centimeters to I guess a few millimeters. It’s such a huge difference. While some millimeter, a millimeter or two and you’re out again, right?

Pamela: The thing to remember is there is a ton of differences in what lines you can see at each of these little fine gradiations. Just going from a few hundred nanometers say 300 nanometers out to 800 nanometers, you’ve now grabbed most of the light looked at by a typical visual telescope. That’s a very small region of the electromagnetic spectrum.

Fraser: That’s true, who am I to complain about a few millimeters when the visible spectrum fits within nanometers?

Pamela: Right so it is all about how much you break up the light. With submillimeter we still are able to break it up a lot within those small regions that we can measure on a meter stick basically.

Fraser: The other side of the submillimeter is infrared? So we’re in-between infrared and radio?

Pamela: Yes.

Fraser: Has it always been sort of considered its own separate wavelength? I guess we’ve got microwave too, right?

Pamela: Microwave actually gets lumped in with the submillimeter a lot. What makes submillimeter what it is we have this tendency to break things up according to how hard they are to look at in some ways.

So, we have visible light [Laughter] which we can see with our eyeballs. Infrared light which we can still detect with detectors very similar to the ones that we use for visual astronomy and snakes see in the infrared so that’s not all that different.

Fraser: I get it though it’s like we can’t see it with our eyes therefore it is a different wavelength. It’s another region and the same with ultraviolet I guess?

Pamela: Right and then when we get to radio. Radio is nice big blocky wavelengths that you can use nice big chicken grate detectors if you want to detect.

Submillimeter, in the last show we mentioned that you have to have a surface perfect to within one part in 20 of the wavelength you’re looking at. With submillimeter dishes we need to be able to build in this case using technology similar to a radio dish.

We need to be able to build it so that the surface of this radio dish has no imperfections that are even the size of someone leaving behind a dollop of metal the size of a strand of hair.

Fraser: Then if I looked at a submillimeter telescope what would it look like?

Pamela: It looks a lot like an overly massive radio dish. Because the surface has to be so perfect, they’re a lot more fortified than your typical radio dish. They are solid surfaces unlike radio dishes that often have big holes in them.

If you look at Arecibo it has big holes in it. They are perfectly solid surfaces and they are really well fortified so that as you tilt them there is absolutely no movement in the surface of the dish. They’re rugged, they’re robust…

Fraser: So it’s really like a cross between a mirror and a radio dish. It has the perfection of a visible light mirror but it sort of functions in the same way as a radio dish?

Pamela: Exactly. Radio dishes you can pretty much stick anywhere and use any time of day. It is convenient that way. Radio light quite happily passes straight through the atmosphere, straight down to the surface of the earth, goes through clouds and doesn’t care if there is daylight. Radio is easy to detect.

Anyone listening if they wanted to could go to Radio Shack and get all of the components to make a radio dish and go outside and detect Jupiter or check the center of the galaxy.

With submillimeter though, we have to start worrying about the amount of water in the atmosphere because water molecules in the atmosphere are capable of blocking submillimeter light.

You have to get yourself someplace exceedingly dry and you also want to be at a high altitude so you can get as much of the atmosphere as possible below you.

Fraser: Once again it is very much the same techniques for putting together a visible light telescope top of a mountain, in the middle of Antarctica, or out in space.

Pamela: It is even worse for submillimeter. We don’t actually launch them into space because there are things that we can’t observe from Earth at all but we do stick them on tops of mountains.

With visible light, the atmosphere just smears the light out which is inconvenient but we can at least look through the atmosphere. With submillimeter light the atmosphere actually flat out blocks the light.

We measure the amount of water in the atmosphere by how many millimeters of ocean it would make if you decided to take the entire atmosphere all at once and turn it into an ocean.

If you have enough water in the atmosphere above the telescope to just make a sea 4 millimeters deep that can block out more than 50 percent of your light, more than 80 percent of your light at some wavelengths.

We just can’t get the light through the atmosphere unlike visible where it is just blurred out and you’re sad.

Fraser: So just to use sort of an analogy when you talk about the radio wave. You point your detector at some spot in the sky and you either get radio or you don’t have radio. It is very binary.

Pamela: Right.

Fraser: Does submillimeter work the same way?

Pamela: Submillimeter works the exact same way. If you have a single dish you look at a single point.

Fraser: Right, if it is working the same way you’re either getting your signal blocked by or decreased by water or not?

Pamela: Yeah and that gets kind of frustrating. So, the best submillimeter telescopes in the world are in neat places at the tops of cool mountains. There is one in Spain called IRAM that’s actually the middle of a ski resort.

Astronomers will be sitting there observing away and watching people ski past their telescope. That’s just amusing.

Fraser: That would be a hard temptation to resist I think. [Laughter]

Pamela: Yes it would. There is also a really good one out in Hawaii that is owned by Caltech and a consortium of universities.

We’re also in the process of building as a community a brand new one in the Atacoma desert which is where the Very Large Telescope is located.

Fraser: Let’s compare and contrast then the functions of a submillimeter telescope. We talked a bit about how the radio works. It scans the sky in a certain region and measures the strength of a radio signal but it doesn’t create an image.

It is only by successive sweeps across the sky you actually build up an image. How does the submillimeter detectors work compared to it?

Pamela: The submillimeter generally works the exact same way. When we combine multiple dishes then we can start to build an image all at the same time. But a single dish working with a single receiver at the same time, you get basically one pixel on the sky.

There are detectors that are working to figure out to essentially multiple pixels. In general it is basically one dish one pixel. It’s when you combine multiple dishes and use interferometry that you’re able to build up simultaneously much more complicated pictures.

Fraser: That’s kind of strange because infrared telescopes work the same way that visible light telescopes work. You point it at the sky and it can make an image.

Pamela: It is a matter of we’re still trying to figure out how do you build the multi-pixel detector for a radio dish. We’re just not quite there yet.

Fraser: I guess the most important question is why on Earth are we developing telescopes to analyze this teeny tiny part of the spectrum?

Pamela: So we can look at lasers in space!

Fraser: Space lasers.

Pamela: There are more reasons than that. You can use submillimeter to look at a bunch of molecules but one of the coolest things is there are naturally occurring microwave basically lasers. Lasers is light processes, microwave is a type of light.

There are places in the universe where for a variety of different thermodynamic complicated reasons the electrons and the atoms end up in an energetically inverted state. You end up with a bunch of electrons that for a variety of reasons ended up at a higher energy level than they should be at if the system is in equilibrium.

As these electrons cascade down to lower energy levels they met a laser beam and that’s just kind of cool. We can use this to study a variety of different environments.

There is a classic pulsating variable star. They are semi regular we’re not entirely sure how they work called Mira stars. There was a lot of press about Mira itself a few years ago because as it is shooting through space it is leaving behind bits of its atmosphere and it is basically a stellar comet in some ways.

In the atmospheres of these stars we actually get these maser processes taking place. We also find this in clouds of interstellar material. We can also use submillimeter to look at a variety of different molecules that we don’t see any other way. We’re just studying a different part of the cold molecular universe.

Fraser: You said that it shoots off like a laser so wouldn’t we see that invisible light?

Pamela: When I say laser it refers to the thermodynamics of the system. It refers to any system in which you end up with more excited electrons than non-excited electrons and a certain type of resonance where you end up with all of these electrons jumping to lower levels and emitting light.

Fraser: Right but you’re getting a coherent beam of photons.

Pamela: It doesn’t have to necessarily be a coherent beam but you have a coherent thermodynamic process that is releasing all of these electrons. When we make these things in the laboratory we end up with a nice coherent beam.

The universe doesn’t generally shoot lasers like you see in Star Wars but it does have this coherent emission of light just like think of it at a spherical laser beam.

Fraser: Then why is the submillimeter the great tool for looking at this?

Pamela: Because the electrons and a bunch of different molecules just happen to have these transitions for the electrons occurring at energies that emit light in the microwave. The microwave is part of the submillimeter.

It just happens that for instance silicon hydrogen molecules, a molecule with one silicon atom and one hydrogen atom happen to have a transition that creates a maser situation.

It’s just a matter of some things emit things in colors we see with our eyes and some times they emit things that we see in the submillimeter. We have red lasers, green lasers and microwave lasers. That’s just one of the neat things about thermo is it allows all of these different colors to exist.

Fraser: Just to reference last week’s show so you’re saying that if I kind of did the math as the electrons stepped down in their energy levels, they’re emitting these photons, right?

Pamela: Right.

Fraser: And the amount of energy in the photon relates to the submillimeter wavelength. Is that right?

Pamela: Yes.

Fraser: If I look out into the universe in this very tight focused sort of part of the electromagnetic spectrum and I see a source that is bright in that then I can assume that this very specific process is going on thanks to the genius theorists who [Laughter] worked up the math to figure it out.

If you see light at this very specific wavelength then that means that this interesting thing is happening. So what were the interesting things that were happening? We talked about Mira which is a pretty amazing star but what exactly is going on do you think?

Pamela: It is basically a situation where you end up with the material is getting bathed in light of just the right temperature or color – we use them interchangeably – from some other source that it is bumping electrons up to a higher energy level.

Lasers and masers have this weird you can’t just bump things up one energy level you actually need to bump them up a couple. Then there is a multi-decay process. It just happens to be that the light flooding this region is of the right energy to set up the population in the wrong set of energies.

If you look at the temperature of the system, the electrons want to be at one energy level. Then you start hitting them with light and the light excites the electrons to a higher energy level. As they cascade down you can end up with this laser maser situation being given off.

Fraser: And maser that’s…

Pamela: It’s just a microwave laser basically.

Fraser: It’s like mega-laser [Laughter] microwave laser.

Pamela: There are people who are trying to change the terminology to mean molecular laser because any of these that are taking place in the microwave wavelengths are actually molecules doing the excitation.

Fraser: Right, okay so that’s one thing that the submillimeter is good for. What are some other things that you might want to look at?

Pamela: There are also different molecules in clouds of cool gas that are giving off their light in submillimeter. This is where we can start looking for formaldehyde in space just in case you want to go pickle something.

We could also look for various carbon organic molecules in space that give off their light in cool clouds of molecular gas in the submillimeter.

Fraser: The same deal here, we’re seeing electrons changing in energy levels and giving off photons in a very precise wavelength?

Pamela: In general with molecules it’s not even the electrons that are jumping up and down levels. But because you have this system of multiple atoms working or bonded together I guess is the best way to put it, they can be vibrating.

As the atoms vibrate, and they can also be rotating, so as the system rotates or vibrates in different ways it has different energies. If it changes from vibrating one way to vibrating another way like a string getting plucked a couple of different ways you can end up with different energies tied in and an electron being given off as it changes the vibrational or rotational energies.

Fraser: It is amazing that we can see that and astronomers can know what they are looking at which of these situations they’re analyzing.

Pamela: It gets to be really ugly math. When you take quantum mechanics they start off friendly and they say here is the hydrogen atom and you learn all about the transitions in the hydrogen atom.

Then they make you sad by giving you the helium atom which is more complex. As you continue to take quantum they eventually hit molecules where you cry because you’re dealing with what’s the moment of inertia of different molecules. What are the vibrational levels of different molecules?

It becomes very complicated very quickly. But we have the abilities if you chew through enough math and use enough computers we have the ability to figure out what are all of these different energy transitions.

Fraser: Wow and so is there some stuff that is maybe closer to home? It sounds like a lot of that stuff is way out in deep space. You’re looking for clouds of molecules or anything useful here in our solar system. Is there any way to observe moons, planets, anything there?

Pamela: Submillimeter is just the study of cold stuff basically. Comets are conveniently nice and cold. In looking at them in the submillimeter we’re able to trace out the nucleus of comets.

We’re also able to look out at the small cold bodies in the outer solar system where for instance and I can never pronounce this poor small body’s name correctly or however you say the small thing that begins with a ‘q’ that is near Pluto. It is something that has been imaged in the submillimeter and we can use this to measure the diameter of these different cold bodies.

Fraser: In this case we’ve got objects that are at that perfect temperature. They’re so cold that the radiation that they’re giving off is in the submillimeter. So it is the perfect gadget for finding those bodies out there. That’s pretty cool.

Pamela: So while we see them in visible, we can see them and learn a little bit more about them in the submillimeter as well. We also use the submillimeter for other things.

We can use it too to look at the envelopes of evolved stars. That’s what we’re doing when we look at Miras. We can also use it to study star formation.

Fraser: Isn’t that a hot process?

Pamela: Stars start off somewhere and they don’t start off particularly warm. Quite literally what’s cool is when you take a giant molecular cloud and let it begin to condense. You start to see the nuclei of stars forming or in this case the protostars forming as small points of heat that appear in the submillimeter.

Fraser: Oh, so because they start out as completely cold clouds and then they start to form and start to heat up and then you’ll see them in the submillimeter. Then they’ll pass that and become hot enough where you’ll see it in infrared and eventually visible light when the star itself appears.

Pamela: Right and we’re also using submillimeter to look at [Laughter] this is going to sound strange but at gamma ray burst afterglows. We’re able to provide some constraints on what is the physics involved in the system around the gamma ray burst as we look at it in a whole variety of wavelengths.

We look at them in the gamma rays, in the x-rays, in the optical, in the infrared and in the submillimeter as well. It’s only by observing objects across all of the different colors of light that we can get a full physical understanding of what is going on in this system.

Fraser: Just a last thing, I want to talk a bit about the hardware, the technology out there that does this. What are some of the observatories?

If I’m reading the news or Universe Today for example, and I [Laughter] see an instrument or observatory mentioned what would sort of let me know that the trigger that okay that’s a submillimeter observatory?

Pamela: It is kind of hard to know when you’re reading through a newspaper if you’re dealing with a telescope that can do infrared in submillimeter or submillimeter in radio and what wavelength it’s working at unless you read the details and happen to know which molecules give off light at which wavelength.

Fraser: And if they mention the wavelengths in the article?

Pamela: Right.

Fraser: We were studying at the point zero five millimeter wavelength…. [Laughter] like “aha! That’s submillimeter!”

Pamela: Some of the big facilities for instance IRAM in Spain which I already mentioned, the Caltech submillimeter observatory. They are working on building the brand new Atacoma submillimeter telescope down in the Atacoma desert. Herschel when it launches is going to be able to work in the submillimeter. We have the Antarctic submillimeter telescope.

There are a variety of them scattered around the world. There are a variety of radio dishes that when push comes to shove can push themselves just barely into the submillimeter if they need to. The real neat experiment that is coming up is the Atacoma submillimeter telescope that is getting built slowly but surely and its first dish was actually delivered in December of 2008. It’s actually starting to show up out there.

Fraser: It is interesting to see sort of as now astronomers are using more and more of the spectrum slices of it are getting a lot of attention. They’re getting dedicated instruments, dedicated observatories. They’re getting some serious attention which is great. There are some amazing new observatories.

I don’t know if this has somehow turned into a tour of the electromagnetic spectrum. [Laughter] There is some really interesting stuff for x-rays and gamma rays. I think we could kind of try and mention that in the past there was sort of like telescopes that looked at light.

Then they figured out there are radio telescopes. But now they’re really slicing it up and saying let’s just focus on this tiny little wavelength and let’s be able to draw the best science we can. Like you said make our force our big radio telescope to drive down into the submillimeter.

Let’s make a really good submillimeter telescope that is finely tuned like a mirror, like a visible light telescope but can receive in that spectrum. It is just great the one in the Atacoma is going to be amazing and Herschel as well.

Pamela: Herschel is going to be amazing.

Fraser: On many fronts.

Pamela: But it is dedicated to one fairly narrow science. What’s amazing about the Atacoma Large Millimeter Array which is generally called ALMA is this is a major international project with the UK, the European Southern Observatory, the Japanese National Astronomical Observatory and the U.S. National Radio Astronomical Observatories all working together building in fact three different types of receivers and transporting them out to a desert plateau.

You really don’t get more difficult than getting many ton instruments to the middle of nowhere. This truly defines the middle of nowhere.

Fraser: Right and if it was a big radio telescope you could tweak it a little. These have to be kept very, very perfect, moved carefully.

Pamela: It is a huge number of dishes and it is going to be years putting it all together.

Fraser: When it is done…

Pamela: Yeah, once they get these 50 to 60 different antennas all installed out on the plateau the universe is ours to observe.

Fraser: No kidding, it’s going to be a monster. That’s great. Well, thanks a lot Pamela we’ll talk to you on the next show.

Artist's impression of the ALMA array

Last week we examined the largest wavelength in the electromagnetic spectrum: radio. This week we get a little smaller… but not too small! And look at the next step in the spectrum, the submillimeter. Astronomers have only recently began exploiting this tiny slice of the spectrum, but the payoff has been huge.

Ep. 131: Submillimeter Astronomy

• Submillimeter Astronomy — U of Arizona
• The spectrum of light — UIUC

Submillimeter Telescopes

• Caltech Submillimeter Observatory
• Institut de Radio Astronomie Millimetrique (IRAM)
• Atacama Large Millimeter/Submillimeter Array (ALMA)
• James Clerk Maxwell Submillimeter Telescope (Hawaii)
• Smithsonian Submillimeter Array  (SMA– Hawaii)
  
• Submillimeter Telescope (SMT — Arizona)
• South Pole Submillimeter Telescope
• Balloon Borne Large Aperture Submillimeter Telescope
• Stratospheric Observatory for Infrared Astronomy SOFIA

• Naturally occuring microwave lasers, or masers
  
• Mira Variable Stars– Internet Encyclopedia of Science
• Observing comets in submillimeter
• Kuiper Belt Objects in submillimeter
• Quaoar
• Paper:  Problems of Star Formation Theory and Prospects of Submillimeter Observations
• Star Formation History of Submillimeter Galaxies -- BLAST
• GRB afterglow observations in submillimeter

Download the transcript

Transcript: Submillimeter Astronomy

ESO Very Large Array. Image credit: ESO

When it comes to telescopes, bigger is better. But bigger is more expensive. Way more expensive. To keep the costs reasonable while improving the sensitivity of their instruments, astronomers use an amazing technique called interferometry. Instead of building a single huge telescope, you can merge the light from several telescopes to act like a much larger telescope. It's a technique that has already revolutionized Earth-based observing – but just wait until it gets into space…

Ep. 129: Interferometry

• Interferometry– JPL
• Episode #85:  Detectors
• Observable Universe — Wise Geek
• Kuiper Belt Objects — Nine Planets
• Episode #41: Rise of the Super Telescopes
• Segmented mirrors – Wiki
• The Giant Magellan Telescope
• Waves and Particles -- Colorado University
• Constructive Interference – Windows to the Universe
• Collimated light
• The Very Large Telescope Interferometer
• Video:  First Fringes of the VLTI
• PowerPoint presentation on Radio Interferometry by Jeffrey Kenney at Yale
• Terrestrial Planet Finder
• Atomic clocks – How Stuff Works

Download the transcript

Transcript: Interferometry

Fraser Cane: When it comes to telescopes bigger is better. But bigger is a lot more expensive, a lot more expensive. To keep the costs reasonable while improving the sensitivity of their instruments, astronomers use an amazing technique called interferometry. Instead of building a single huge telescope you can merge the light from several telescopes to act like a much larger telescope. It is a technique that has already revolutionized Earth-based observing. Just wait until it gets into space.

Okay Pamela, when I wrote that intro I kind of wanted to like not scare people. [Laughter] Interferometry, don’t let the title scare you. It is one of the coolest technologies that has been developed in kind of modern astronomy. I think it has led to part of this golden age that we’ve been talking about in astronomy.

As I said wait until we get to the space missions. Let’s talk about first the dilemma of building a gigantic telescope. What are kind of the limits of telescope technology right now?

Dr. Pamela Gay: You build giant telescopes for two basic reasons. One reason is you can get just so much more light. The more light you collect with your mirror, with your dish, with whatever light collecting surface you’re using, the fainter an object you can look at because you are getting more photons from that faint distant object or even that faint nearby object.

Cameras require a certain number of photons before they can go “yes I believe there is light here”. At the same time you also want to have high resolution images. You want to be able to make out the separation between close stars. You want to make out the details in galaxies. You want to be able to see all the bumps and wiggles in patterns of star formation regions’ blobs of gas and dust.

Both resolution and light collecting area depend in different ways on the radius of the telescope. For the light collecting area it is simply how much light are you gathering; it is what is the area of your detector. With resolution, all it cares about is how far apart the two edges of your detector are. How many wave lengths across is your detector? What’s cool is when you’re figuring up the resolution of the detector the detector doesn’t actually care if the middle part is there or not.

You can get the exact same resolution with a giant donut shaped mirror that is only maybe 4 inches wide in the donut part and 10 meters across from outer edge to outer edge as you’d get from having that entire solid mirror. That donut, amulus of mirror is going to weigh a lot less, is going to cost a lot less to produce and it doesn’t even care if it is a contiguous donut.

I could actually instead of having this ring of mirror, this ring of collecting surface; I could instead have maybe 4 different dishes at the north, south, east and west equivalence of that giant donut. As I break down to smaller and smaller areas, it gets cheaper and cheaper to build.

Fraser: Give me an example then of something where you want a lot of photons.

Pamela: A lot of photons are I’m trying to observe a galaxy at the very edge of the observable universe. This is a very faint object, very far away. We’re just not getting a lot of light. Here we want to collect more and more light or I’m trying to observe faint quiper belt object.

One of these blobs of frozen ice that is out around the orbit of Pluto, a very small very not necessarily reflective object I need to collect as much light as possible to try and see if it is there at all.

Fraser: Okay so it is like every photon is precious and if you can’t collect the photons you don’t even know that the thing exists.

Pamela: Exactly.

Fraser: What is the situation where high resolution is key?

Pamela: I’m looking at the star Betelgeuse. It is near enough by that if I use a high enough resolution detector I can actually make out the disc of the star. I can look at it and go, oh star spot.

I can look at it and I can measure how big it is. I know the distance to Betelgeuse and this allows me to actually calculate the physical size of the star.

Fraser: Then in this example Betelgeuse is giving off plenty of photons. No more photons are needed but the key is that you need to be able to have your resolution to be able to see the disc of the star, to be able to see sunspots.

As in the case as you mentioned before some kind of binary object where you’re trying to sense the separation between two stars. So then the traditional way is to build a big telescope. We talked this a bit in our rise of the super telescopes episode. Prices rise exponentially as the size of the telescope increases, right?

Pamela: Not only that but just the mechanical skill needed to get bigger than we are currently able to build, we’re just not there yet. Some of the largest telescopes in the world right now have 8 meter to 10 meter mirrors. These giant mirrors are right at our limit to spin cast them, to transport them to mount them so that gravity doesn’t deform them.

As we get to bigger and bigger mirrors we’re going to have to develop new technologies in using segmented mirrors; building new mount systems and being able to handle all of this weight without gravity deforming the systems. We’re reaching a point where engineering problems just as much as cost problems make it prohibitive to build these giant telescopes.

Fraser: There are plans in the works for 30 meter telescopes which will have all of these segments kind of lashed to make one great big telescope. The cost on that telescope like the Magellan is going to be enormous. You’re really kind of reaching the feasible limits but that is like a big light pocket right?

A big telescope like the Magellan is going to give you a 30 meter telescope to collect a whole lot of photons. That’s going to be seeing these faint quiper belt objects in these galaxies at the edge of the observable universe. Then here comes the solution, interferometry. So, what is interferometry?

Pamela: Interferometry basically goes light is particles that also act like waves. If you combine waves in a meaningful way, making sure that the peaks of one wave line up with the peaks of another wave they interfere in a way that we call constructive interference.

In this way you can collect a bunch of waves, line them up and it’s just as though you’ve collected all the waves at the exact same time. This sounds like a relatively simple idea. I go out, I collect my light, I somehow maybe using fiber optics, maybe using mirrors recombine this light and everything works.

Fraser: That’s kind of funny because it kind of sounds like gibberish to me. Let me just kind of parse this because I barely am wrapping my head around it.

You’re getting the light from one location and you’re getting the light from another location. You’re putting that light together? Is that right?

Pamela: Yeah.

Fraser: Then you are sort of seeing how the waves, as you said they construct or destruct one of those. I remember in physics we had the situation where you have waterways and you have two waves running into each other and if the two peaks come together then you get a double wave.

If the peak and the trough come together then you get flat water. I know light works the same way so I’m having trouble understanding how you can take light from two different positions and merge it together.

Pamela: This is where it gets very tricky. We’re really good as astronomers at doing this with radio waves. We know how to tune our receivers. We know how to detect the peaks and the troughs and the wave patterns very well.

With detectors like the Very Large Array, they know okay so the object is over in that part of the sky so I tilt all my dishes towards that object. I know exactly where on the surface of the Earth all of my telescopes are located very precisely.

I can use geometry to figure out this dish at this angle is this much closer to the object being observed; this other one is this much farther. They use different travel paths, different computers to take the signal from each of these telescopes and combine it with delays that allow the radio light that is received by each of these dishes in a slightly different location to be mixed. So it is as though the light was hitting each of the dishes that have left the object at the same time, hitting the telescope at the same time using artificial delays.

These artificial delays allow the peaks to stay lined up with the peaks and the valleys to stay lined up with the valleys and to get constructive interference and to artificially create a giant telescope aperture that gives you these extremely high resolution images.

Fraser: Are the two telescopes recording the same photon? You know, light could be a wave and you’re saying you’re trying to line up them together. Is that what’s going on that the photon is spreading out over a large area and so it is hitting the two telescopes and that is how you can kind of get at your better resolution? Is that what’s going on?

Pamela: We talk about light being what is called columate. This means the light that is coming off of an extremely distant star in an extremely distant galaxy, the light that is coming off of the source has the peaks and valleys within it lined up so that you get a coherent light beam.

So, they’re not detecting the exact same photon in two different dishes, but we’re detecting photons that are acting together in a columated fashion such that if I don’t have the moments at which I’m recording my data artificially lined up then I’m looking at a packet of photons that were released at one time, a packet that was released at another time. The peaks and valleys from these two different times might not be lined up.

I can get like you pointed out a trough lining up with a peak which gives me no light at all. It’s because it is coherent light coming off of the source that acts in what we call a columated fashion that we have all of these peaks and valleys, peaks and valleys lined up as the light travels through space.

Fraser: The timing is the key.

Pamela: Yeah, we have to maintain that lined up and we do it by shifting the signal from the telescopes until it is as though all the light was hitting the telescope at the same time.

Fraser: I guess I find that kind of, I’m sorry, I find that a little confusing as to why you say it is a columated light. I guess I find that part just a little confusing. A lot confusing which is why that is important?

I guess I understand if you don’t have the timing then it’s kind of like you have a telescope over here and a telescope over there. This one is taking images, that one is taking images that you could merge the images together – and this is what a lot of amateur astronomers do, right – they run video of some object that they’re trying to collect.

They take frame after frame and then they use image stacking software to kind of stack the images together to get a longer exposure but also to be able to remove the bad frames. That’s not what this is about.

Pamela: No.

Fraser: This is not taking two separate telescopes and merging the light together until you’ve got a thousand photons on the right telescope and a thousand photons on the left telescope. You put them together and you get a little bit better image. This is different. I think that is important.

Pamela: This is getting at increasing the resolution of the image.

Fraser: Right and as you said it is key to the fact that the photons were emitted at the same time and are connected is the way to put it?

Pamela: Connected is not quite the way to put it. First of all you do have the object varying. In theory I could take light from two different telescope dishes and combine it so that I have the peak of one wave combined with the peak of the next wave. In theory I’ll still get everything interfering in a way that allows me to get nice good sharp image.

But I’m observing the object in two different periods of time so I want to get a snapshot of the object in the now such that all of this light that I’m receiving traces the same behavior in the object.

There is also a matter of the resolution is directly related to how wide is my aperture. How wide is my reflecting surface? In this case that width is a reflection of how many wavelengths fits across the telescope.

If I have a ten meter optical telescope, it is going to have absolutely amazing resolution because optical light is extremely small. It is hundreds of nanometers. These are smaller than anything that you can believe or imagine because it is smaller than what you can see with your eye.

We have something that is several hundred nanometers peak to peak whereas with radio wavelengths I can have a ten meter dish and very, very poor resolution. An entire galaxy is nothing more than one pixel of well, this is light, this is dark. No you can’t see any details, all you know is there happens to be an object that emits radio over there somewhere.

This is because the radio wave ones are meters and meters in length. I’m trying to compare something that is hundreds of nanometers to something that is tens of meters in size. This is such a huge difference and it means a huge difference in the resolution.

Fraser: I think that is key though, that this is very tricky. With optical telescopes to line up the wavelengths between two optical telescopes you have to make sure that your wavelengths that are nanometers across are perfectly lined up.

That requires timing at an insanely complicated level. While you can imagine these radio wavelengths which can be meters across where you can kind of miss a little bit and it’s no big deal. To use this technique radio is the larger wavelength is where it really shines, right?

Pamela: Conveniently it is the radio wavelengths where we need this technology the most. A single dish has such terrible, terrible imaging resolution. It is only by starting to combine dishes that are actually spread across half the globe that we’re able to start getting really good resolutions.

One of the amazing things about this is with radio telescopes we’re able to very precisely record incoming radio light from distant objects in New Mexico, Massachusetts, and in Spain. Using dishes spread across the entire part of the planet that are capable of looking at some distant object at the same time we record the signal onto hard drives onto magnetic tapes. We record the timing of the observations.

Then artificially in a computer combine all of this light in a process that involves this neat thing called fringe finding where you carefully adjust the timing offsets between the data. We artificially combine everything to create this artificially large telescope.

With optical light we don’t have the ability to record the incoming light in the same way where we’re able to keep track of every peak and valley, every change in incoming photons. It is because of this difference where we end up resorting to things like using fiber optics where we physically delay the light travel time to the detector and physically combine the light so that it has the correct delays from one telescope to another.

Fraser: Let’s talk a bit about sort of what the set up of one of these inferometers looks like. There are a couple operating now and so sort of the visible light telescopes lay it out for us. What does this kind of look like?

Pamela: Visible light is still very, very experimental. There aren’t many systems in the world that are getting actively used for things that you and I would be able to see easily with our own light. The most famous of the systems is the Very Large Telescope Interferometer down in Chile.

We have the large 8.2 meter telescopes in the Atacama Desert that have the ability of using fiber optics, combine the light and get extremely high resolutions along what we call the baselines. These are the lines connecting one mirror’s center to another mirror’s center.

When you combine two telescopes you get extremely high resolution only along the direction in the image that has from one edge of one telescope to the other edge of the other telescope. Then you’ll get single dish resolution 90 degrees to that because we don’t have that added size to the telescope mirror in that direction of the telescopes aren’t spread out from one another.

Fraser: It’s like imagine a big long skinny telescope that is 8 meters high and how far apart are they?

Pamela: These are actually about 200 meters apart.

Fraser: Okay so it is 8 meters high and 200 meters wide. It is a very long skinny mirror. As you said it can go the other dimension too, right?

Pamela: Right so here they have multiple telescopes and they also have the additional little one meter telescopes that they can move around the facility and add in additional rays to end up getting as many as six different dishes on at the same time I believe.

By combining different mirrors in different ways all of this working in the optical – well here I have to say it is kind of a cheat to say the optical – it is the optical if you’re a snake.

This is near observing. There are systems that are working in what we do see as visible light but these are mostly systems that are still experimental. We’re still working on developing this technology.

Fraser: Right, the future has yet to be written.

Pamela: There are experiments in Sydney, in Hawaii, there are experiments all over the world trying to make this work invisible light but if you’re a snake, it is visible because we do have the strength you need for that.

Fraser: So, infrared and down sub millimeter into the radio microwaves, you’ve got the ability to merge these telescopes. As you mentioned the most amazing example of this is the fact that one whole half of the Earth can be called upon as one great big radio telescope. If what you need is a telescope the size of the planet there’s one available to you.

Pamela: Right and with the radio, we’re already doing this. We already have plans or at least different people have put together different plans, no one is working on building them at least right now that I know of to extend the baseline by putting dishes in orbit.

The plan to extend the baseline where instead of being confined to the diameter of the planet Earth, we’re instead confined to where in the solar system that we put our telescopes.

Fraser: We could put up one radio telescope on one side of the Earth’s orbit and another on the other side…

Pamela: Or stick one out on the moon. There are lots of different ways that we can start combining things.

Fraser: Right and the resolution goes up. Then there are plans in the works to develop space telescopes that would use interferometry. I guess our favorite cancelled space program that was where they were being planned, right with the terrestrial planet finder?

Pamela: Yes. This was the system that was looking to combine the light from three different telescopes to a central observing hub. It is a complicated system but in space it is using its lasers to very precisely locate the spacecraft.

We can get them spread out to much larger distances. Again this was a system that was looking to physically combine the light along these different path lights using physical delays.

We know how to do this. It’s not easy to do. It’s not cheap to do and this is why NASA hasn’t quite gotten around to actually doing it yet.

Fraser: Alright and I think the terrestrial planet finder this is one of those situations where the resolution is what you want. You want to be able to resolve a planet orbiting a star where it is a separation issue.

Obviously you want some photons but you really want to be able to just acknowledge its existence there. That’s not simple.

Pamela: Here we have to be able to resolve the planet separate from the star. We have to be able to block out the light from the star. It starts to become increasingly a more and more difficult system.

Fraser: When I first heard of the concept of interferometry I got really excited. I wondered if you could take, kind of like SETI at home. Amateur astronomers around the world could set up their telescopes, point it at some object that they’ve all been instructed to point it at and then gather light for whatever period of time.

They would then submit their images to some central clearinghouse that could then merge it all together to do interferometry in the visible spectrum. I emailed this to several scientists and I got some like polite laughter. [Laughter] Where was my thinking incorrect?

Pamela: Like I was saying earlier with the optical light the problem is we can’t just artificially recombine it later because you’ve been able to record with your CCD detector the over time variations and the life of peaks and troughs quite so conveniently.

With light you’re collecting photon after photon after photon and building an image with long integration times. You don’t do that in radio because the technology is just completely different. On top of that there are also all of the timing issues all of the positional issues.

This means that you can’t even do what you are suggesting if we replace all of the 12 inch amateur telescopes in people’s back yards with instead satellite dishes taken from the local cable television networks.

The issue with Inferometry is you have to know exactly the surface of the planet. You have to have atomic clock precision in the timing of your observations. Even with that, combining the data can be difficult to say the least.

The process of fringe binding the process of artificially lining up the radio data to get it to coherently combine, to get the peaks to line up with the peaks to enhance your signal is a complicated process. As you bring in the light from each different dish if you’re using for instance baseline interferometry you have to worry about things like the Russian’s telescope is off by three seconds. You have to worry about oh Spain was behind by half a second.

All of these small differences in timing have to be accounted for and they end up affecting your data as your telescopes move across the sky in several different ways and it is just hard to combine all of this data.

As you bring in more and more telescopes all of these small time issues become more and more things you have to worry about. It just becomes an untraceable puzzle fitting nightmare that no one wants to solve.

Fraser: It would work if we gave everybody an atomic clock and connected their telescopes by fiber optics and measured their position on the planet to an insane accuracy. Plus we would need to develop entirely new technologies and new kinds of computers.

Pamela: And we were able to wire the fiber optics in just the right way that we were able to exactly compensate for differences from multiple objects with multiple differences and travel time delays. It is just far too complicated of a problem.

Fraser: With radio dishes, it would be feasible.

Pamela: It’s all about the computer power there. Even then you would have to give everyone on the planet an atomic clock and military grade GPS.

Fraser: Oh well, all in the name of science. I’m up for it. [Laughter] Cool, well I think that this is going to be one of those technologies that over the next couple of years they will keep on developing the techniques.

They are going to crack it and I think that you’re going to really see some amazing research from ground-based telescopes and especially the space-based observatories that are hooked up in these baseline arrays. That’s going to really be amazing.

Interferometry – it is a complicated word but it is a very exciting technology. Read the stories when you hear something about some interferometer that comes online. It could be the next great technological advance. Thanks Pamela and we’ll talk to you at the next questions show.

Pamela: Sounds great Fraser, talk to you then.

SDSS Telescope

In the old days, astronomers had to beg for telescope time. They'd put together a proposal, convince observatories to gather data for them, crunch that data and release the results. No telescope, no results. But everything's different now. Fleets of robotic telescopes constantly scan the skies, building up a vast database of raw data about the Universe. Anyone who wants can access the information through the Internet, download what they need to do real science. No telescope necessary. Let's look at the development of sky surveys, and how they're changing how astronomy gets done.

Ep. 118: Sky Surveys

• TEXOX Survey of Radio-Selected Galaxy Clusters (Pamela's doctoral dissertation project)
• McDonald Observatory
• Palomar Observatory Sky Survey – a comparison of POSS to the Sloan Digital Sky Survey
• Digitized (and searchable) version of POSS from the Space Telescope Science Institute
• The Second Palomar Sky Survey
• Sloan Digital Sky Survey
• Apache Point Observatory (where the SDSS is done)
• Sky Server (to search for SDSS images, as well as educational materials)
• The drift-scan technique
• Tidal tails – Internet Encyclopedia of Science
• co-moving:  indicates a state of expansion or contraction matched to that of the universe as a whole.
• SDSS:  3-D Map of the Universe Bolsters Case for Dark Energy and Dark Matter
• SDSS:  Quasars Found at the Edge of the Universe
• SDSS:  Scientists Discover New Celestial Dwarfs
• Galaxy Zoo
• Galaxy Zoo:  The Science
• GZ and Overlapping Galaxies
• Chris Lintott
• Kevin Schawinski
• VLA FIRST Survey
• Near Earth Asteroid Telescope (NEAT)
• MACHO Project overview
• OGLE (Optical Gravitational Lensing Experiment)  Project
• Sky View Virtual Observatory

Download the transcript

Transcript: Sky Surveys

Fraser Cane: In the old days astronomers had to beg for telescope time. They put together a proposal, convinced observatories to gather data, crunch the data and release the results. No telescope, no science.

But everything is different now. Fleets of robotic telescopes constantly scan the skies building up a vast database of raw data about the Universe. And anyone who wants can access the information through the internet; download what they need to do real science – no telescope necessary.

Let’s look at the development of sky surveys and how they’re changing how astronomy gets done. Is that a little over the top you think?

Dr. Pamela Gay: No, I think sky surveys really are actually changing how everything is done and that’s kind of cool.

Fraser: Why don’t you then regale us with a story of you attempting to get science done the old way? [Laughter]

Pamela: I think the best example is my doctoral dissertation. I was working on a project called the Texox Survey where we were following up on a radio survey actually, looking for places on the sky where we thought maybe there was a higher probability of finding galaxy clusters.

We put in for observing time at McDonald Observatory, first on the 30 inch telescope, then on the 107 inch telescope. Hundreds of nights were spent out at the observatory.

When the weather went bad we didn’t get our data, I attracted clouds, and there was much crying and sadness. We got somewhere but we didn’t get where we wanted due to clouds and forest fires and all that sort of stuff affecting the amount of time we had at the end of the day. It was sad.

Fraser: It still kind of happens now. I know you’re telling me about some projects that you’re working on where you have to scrape together telescope time. You have to convince amateurs to let them do some observations for you.

You’re distracting telescope operators so you can sneak in and you know, quickly move the telescope. [Laughter]

Pamela: There are two different ways of needing to get data. There is the “I have a question that requires significant coverage on the sky. I want to look at a whole bunch of different objects and try and prove something in a statistically significant way.”

To do that you need a ton of telescope time scattered all over the sky. The data that I take might also be good for somebody else. Not the type of stuff that leads naturally to the type of surveys that we’re going to talk about in the rest of the show.

The other type of thing you need is: “Ooh, I found a really cool object! I need a bazillion hours on this one really cool object.” That’s where you start begging people. That’s where you need the dedicated time to look at just your object.

This is why the stable of astronomical equipment needs to include both telescopes that are dedicated to doing surveys, looking at the whole sky night after night and also telescopes that are set aside for astronomers to follow up on pet projects.

Fraser: Alright, let’s then segue into the survey. Cane you give us an example of sort of what was one of the first sky surveys put together? What’s involved?

Pamela: The first really big survey that people paid attention to even today, is the Palomar Observatory sky survey. It used glass plates, two different Kodak emulsions, one sensitive to red; one sensitive to blue to look at pretty much the entire northern hemisphere of the sky all the way down to minus 30 south. It had significant coverage of the sky.

The idea was to catalogue what’s out there. The survey has been used to look for galaxy clusters. It’s been used to get statistics on how many of what different types of objects are out there.

It’s used even today where some cool something or other happens and you pull out the digital sky survey and look to see what was there before. It’s a historic record of what was where on the sky when. It’s a map of the sky and it’s a way to do big science admittedly on the 1940s technological scale.

Fraser: You’ve got a really nice telescope every night, taking a picture, moving a little bit, taking a picture and moving a little bit. It’s just slowly cataloguing every single little piece of the night sky.

I guess as we talked about before to really get good science about an object, you want to point Hubble [Laughter] at it for about a hundred hours and get every stray Photon that’s coming from it. This is the opposite, right?

This is quick and dirty. This is click, move; click move and so as you said you’re able to count up galaxy clusters. You’re able to count stars. You’re able to get a general sense of what’s out there. But you’re not able to really dig deep and see the same thing pointing at one object for a hundred hours.

Pamela: No and in fact with these old glass plate surveys, it took them years to get coverage of the entire sky. Even today we’ve moved on and today’s new version – perhaps new version is too strong a word, but our new optical survey of the sky is the Sloan digital sky survey.

It’s probing the southern galactic pole. It’s looking at a very focused region of the sky and it’s studying extremely deeply. It’s doing it in 5 colors whereas the Palomar sky survey looked at the sky originally in only 2 colors and it’s getting huge swaths of the sky every night.

But to get as deep as it does, it takes significant amounts of time and it takes years to get a really detailed survey of the sky complete.

Fraser: Let’s take a look then at Sloan. When did Sloan get operating?

Pamela: They started building the telescope back in the 1990s and it first started taking images in 2000. It's still here in 2008, reinventing itself, coming out with new ways of doing things.

Fraser: Then what does it capture? Obviously it takes a picture of a chunk of space but I know there’s more information that it’s helping gather, right?

Pamela: The Sloan digital sky survey is using a technique called drift scanning. You might start off with an object on the right-hand of the CCD and over time it slowly drifts from the right side to the left side.

As it is drifting the digital camera is taking that right-hand most column of data and shifting it one pixel to the left and shifting it one pixel to the left. It’s shifting the recording of the data one column at a time at the same rate that the object is moving across the CCD.

By the time it has read all the way across the chip you might have many, many minutes of observations of that particular object allowing you to get extremely deep images all across the sky.

Fraser: Okay, I understand, it’s like the big CCD isn’t moving so it is able then to just pick it up, see the same object again and again.

It’s almost like it’s taking multiple photographs of the same object because it’s grabbing such a big swath of the sky at the same time.

It’s using the rotation of the Earth to move the objects in it through its field of view.

Pamela: Yeah, that’s exactly what’s happening. What’s really cool is in addition to doing this detailed imaging of the sky, the Sloan digital sky survey is also going back and doing follow-up spectroscopy.

In this case they’re actually taking plates and drilling holes in them and then aligning fiber optics onto the holes on the plate. For each hole in the plate and each fiber, they get individual spectra that allow them to get a sense of what elements are in the objects that they’re looking at. What is the red shift of some of the galaxies that they’re looking at?

These are pretty big fibers so while they’re able to capture a lot of light all at once they also aren’t so good for dealing with really crowded fields like galaxy clusters.

But for isolated objects this system is allowing us to sample a huge number of galaxies scattered all across the sky to find out where they are in red shift space. That gives us a sense of their distance and to also give us a sense of what are other things we can learn by looking at the elements.

This starts to play more of a roll when we’re saying does this thing have absorption lines? You can start to differentiate different types of active galaxies by looking at what lines exist in emission.

This is where you have an angry super massive black hole in the center of the galaxy that’s chomping on things and heating them up and if the alignment is just right, the heated up elements end up radiating emission lines that we can detect. That tells us something about what’s going on down in the core of the galaxy.

Fraser: Then how much of the sky is Sloan going to be mapping?

Pamela: Sloan digital sky survey is looking to eventually map out about 25% of the sky. That doesn’t sound like a lot, but at the level of detail they’re getting this is actually a really powerful survey.

Already they’ve allowed us to learn new things about the structure of our own galaxy that we’ve never even guessed at. Galaxies are the cool part for me. In addition to looking at all the galaxies, it’s also mapping out stars in the halo of the Milky Way.

By looking at the colors of the stars we’re able to get a sense of how far away they are. So you look at the color and brightness and basically by taking a color magnitude diagram of what would a population of stars look like at what distance.

You can sample through the sky to find out where are the populations of stars that are 60 kilo parsecs away. Where are they that are 70 kilo parsecs away? We can start to see streaks, tidal tails of shredded dwarf galaxies out in the halo of the Milky Way by probing through using the Sloan digital sky survey data to find what we call co-moving populations of stars.

Fraser: I guess this is where the real power is because in the olden days you would take your telescope, look at a region of sky, and make measurements of whatever you wanted to do.

But in this situation Sloan is gathering images of everything that’s in that 25% of the sky and furthermore they’re writing down numbers. They’re saying: “there’s a star here at this location, there’s a galaxy at that location. There’s a quasar here at this location.” And then they’re figuring out what the elements are that are in those objects. You can then do searches.

This is where it becomes a database issue. You can say: “find me every star that has this level of metalicity, or find me all of the stars that are within this range in this region of the sky.” The data mining starts and perhaps suddenly you look at that line where you mapped out all the stars in the survey and they happen to be lined up in a very interesting line. That must be a tidal tail.

So there are whole new kinds of discoveries being made that could never be made before because you just didn’t have the raw data about the entire sky that you could just then mine and ask questions.

I know there’s some amazing work done for dark matter, quasars, as you said cataloguing active galaxies. Isn’t Galaxy Zoo using the Sloan digital sky survey?

Pamela: Right but before we jump on to galaxies I just want to make it really clear that the spectra that they’re getting with the Sloan digital sky survey really isn’t good enough to start getting at detailed metalicities of stars. It is rough spectra but it’s enough to get us what are their velocities and to get us broad information on them.

That’s what’s cool about the Sloan digital sky survey. It gives us a broad understanding of where things are, of how they’re moving, of what different types of things are out there that we can follow up on later.

It is allowing us to find more white dwarfs than we ever thought we could find some other way. It is allowing us to find quasars. It is in fact allowing us to determine the distribution of galaxies of different shapes and sizes and orientations on the sky. This is where Galaxy Zoo comes in.

Fraser: People are finding asteroids and kuiper objects that are sort of in the pictures.

Pamela: They’re starting to find really rare objects. One of the really cool things that came out of the Galaxy Zoo 1 project, a project that was originated by folks over at Oxford, my collaborator Chris Lintott, Kevin who is now at Yale, a whole bunch of different folks, were sitting around.

Kevin was given the task to go look at 50,000 galaxies and tell us where their distribution is in terms of are they spirals, are the elliptical? How are they oriented? After doing 50,000 objects he really didn’t want to do any more.

So in a pub, the idea was originated to get the public who likes looking at galaxies to look at almost a million objects from the Sloan digital sky survey and catalogue how they’re oriented and what their shape is. Basically are they clockwise, counterclockwise or edge-on spirals or are they ellipticals or are they mergers? They did this and the results of the public looking at all of these objects were just as accurate as getting a small number of professionals to look at a much smaller sample of objects because you can’t make professionals look at too many of them before we go crazy.

You ask 170,000 people to look at things and of course 170,000 people can look at a lot more objects than 5 or 6 professionals.

Fraser: Right and you’re saying that they turned up some amazing things.

Pamela: One of the really cool things that they were able to do is build up a catalogue of galaxies that are overlapping on the sky. These aren’t galaxies that are merging but rather two galaxies that are superimposed on one another’s line of sight, we say. One is nearby, one is further away.

Gravitationally they really don’t care about each other very much, but the background galaxy can act like a spotlight going through the dust lanes of the foreground galaxy allowing us to make out the details in structure that we might not otherwise be able to see.

Fraser: I guess it’s almost impossible for a computer to seek out those kinds of objects because it can barely tell that there’s a galaxy there at all. This is something that a human being is great at.

Pamela: Computers are generally pretty good about determining what is a star and what is not a star. Beyond going not a star, computers tend to get kind of confused.

At a certain level you can start to program them to look for things that are S-shaped or Z-shaped so we have clockwise and counterclockwise shaped galaxies.

We can program them to look for things that have a radial profile, things that are basically fuzzy blobs like elliptical galaxies. You can’t program a computer to determine if this thing looks like nothing anyone has ever seen before. They’d be showing that up every time an asteroid happens to pass in front the galaxy.

You can train human beings to determine what an asteroid looks like when it is passing through an image; this is what a satellite looks like when it’s passing through an image. This is a really weird nebula; this is reflected light inside the telescope.

We can take human beings and train them to do things that we can’t train a computer to do. Human beings will naturally note “this is cool and unusual” and bring it to the attention of other people. That’s one of the wonderful things that came out of the original Galaxy Zoo project. What’s even cooler is there is now a second generation, Galaxy Zoo 2 that’s been launched.

If you go to galaxyzoo.org there is now a link off of it to Galaxy Zoo 2 but you’re going to have to take a survey if you participated in Z1 so that some of the folks working with Galaxy Zoo, which in this case includes me, so please take the survey, can find out a little bit about why is it that you love using Galaxy Zoo. I know why I love using it; I want to know why you love using it.

Fraser: What are some other surveys that are happening?

Pamela: Surveys aren’t restricted to just being optical telescopes. There are lots of other surveys out there. The Very Large Array out in New Mexico is working on a survey called ‘First’ and it’s looking to do both the northern and southern galactic poles.

It’s a survey that’s looking at 21 centimeter continuing radiation. This is the type of light you get from disks of galaxies from blobs of gas. It allows you to see star-forming regions. It also allows you to see jets off of radio galaxies.

The first survey has about 5 arc second resolution which is what you get on a really bad day with an optical telescope. It’s about 5 times what you’d get from a reasonable sight with an amateur telescope. It’s going pretty faint and it’s looking to collect data that will allow us to figure out where are all the galaxies that are actively forming stars.

Where are the most distant radio galaxies – galaxies that are actively feeding black holes in their center and are thus giving off radio emission? This is an ongoing survey that’s constantly working to increase its area and it’s working in radio. It’s just another way of looking at the Universe.

Fraser: So, same deal, right? Gather as much raw data as you can, catalogue it as best you can and then make that information available to the scientific community and I mean the general public – it’s all on the internet – to look for whatever they want in the data as it stands which is just amazing.

Pamela: And we’re working to try and cover as much of the sky as we can and as many different colors as we can. There’s 2MASS out there working in micron radiation that used two 1.3 meter telescopes in Arizona and Chile to look at the sky.

There have been infrared satellites and x-ray satellites that have also worked to cover the sky. We also look at data that was perhaps taken for other purposes as another source of perhaps serendipitous observations.

There’s a telescope called the near-Earth asteroid telescope, neat. It is primarily out there trying to make sure nothing hits the planet Earth. It’s a good goal, but as it is out there surveying for this very specific purpose, it’s also picking up supernova. It’s also picking up variable stars. It’s picking up lots of other stuff that just happens to be in the background of the same fields it is looking for asteroids in. We can use that data as well.

There are very specific surveys looking at very small regions of the sky but because they’re building up data over years, we’re able to learn interesting things. There were two projects, the MACHO project and the OGLE project that looked at the magellanic clouds specifically looking for gravitational lensing events. This is where a nearby object, in this case nearby being on the outskirts of the Milky Way Galaxy, passes in front of the background object, something in one of the magellanic clouds and causes it to brighten through gravitational micro-lensing.

In the process of looking for these events, they’ve also done things like find light echoes from supernova moving through the interstellar medium. So there is a supernova hundreds of years ago, thousands of years ago and the flash of light from that supernova is forming an expanding shell of light. As that light passes through the gas and dust between the stars, it temporarily illuminates whatever section that it happens to be in.

By looking in the same direction for year after year after year, we can watch these shells of light move and then track them backwards and figure out where they originated.

This is one of the neat ways that we’re starting to figure out what was Kepler’s supernova actually like? What was the supernova in Cassiopeia actually like? We’re tracing back the light echoes to learn more about events that we weren’t around to see.

Fraser: This I think is a realm of science that has no limit. You can just imagine bigger telescopes, more telescopes gathering more of the data that are looking deeper. Are there sort of dream projects in the works to do really enormous surveys?

Pamela: What’s really cool is they’re not even dream projects, they’re actual projects. There are two really cool ones coming up, Pan-STAARS and LSST (Large Synoptic Survey Telescope).

These two different many meter telescopes are focused on trying to find things that are going to hit the planet Earth. Protecting the planet Earth is a good way to get money to build telescopes. Along the way while they’re out there taking snapshot after snapshot after snapshot of the sky they’re also going to be turning up supernovas. They’re going to be turning up variable stars. They’re going to be taking image after image of the same place on the sky.

Those images can be added together to get some of the deepest images we’ll have ever achieved of distant galaxies. It’s all a matter of adding up the data over time. With these two projects we’re going to have these huge telescopes taking in pretty much everything that’s visible every single night.

That data can get added up to allow deep imaging or it can get used together to get time sequence imaging to see what are all the transient events that we’ve been missing all these years.

Fraser: I think just to be clear all this data is available on the internet, right? If you know where to look, you can pull it down and crunch it.

Pamela: Different surveys have different proprietary periods. This is a certain amount of time where the people who invested the intellectual resources and the monetary resources to build a given instrument (telescope) or take a certain survey, get to have all the data to themselves. At the end of these proprietary periods all of the data becomes publicly accessible.

One of the greatest ways to go out there and access a lot of this data is through a portal called Sky View. Just open up Google and do Sky View Virtual Observatory. It will give you a form to fill out that will allow you to get radio data, x-ray data, and optical data, all of the same field on the sky.

It will allow you to map different objects onto these images to see where they happen to line up. It’s a great resource for both the professional astronomer and for people who are just trying to get a different wavelengths perspective of the Universe.

Everything is out there. Sometimes you just have to wait 6 months to a year to get your hands on it.

Fraser: I think the big need is for people in the computer industry, people who understand how to make a database sing and to be able to pull in that data and help crunch and help answer some of those basic questions.

But I think the reality is that anybody who wants, assuming they have the skills, can go onto those surveys, download the information and discover brand new objects, discover asteroids that have never been seen before. It’s all there; there are mysteries inside that data. All you have to do is go looking.

Pamela: And I can’t restate what you’re saying with enough emphasis. It is everyday people who are going out and discovering new things in some of these surveys. I’ve been at American Association of Variable Star Observers meetings where amateur astronomers have stood up and given talks on how they’ve gone through this database or that database pulling up variables that no one had known about before just because they knew how to do all the nice equal queries effectively.

With the Galaxy Zoo project there have been just everyday members who are participating and noticing things that are new that are making cool discoveries where go check out the forums. Look up the peas in the Galaxy Zoo forums. These are a new class of galaxies that were discovered by regular people who asked: “What are all these little green compact galaxies?”

There’s new stuff out there just waiting to be discovered. You might be the person to make the next cool discovery.

Fraser: And if you do let us know. We’d love to hear it. Well thanks a lot Pamela and we’ll talk to you next week.

Pamela: One more thing before we quit. Hopefully next summer I will both have my voice back and I will have the opportunity, perhaps with even you, to go out and see a really cool eclipse out in the Pacific Ocean. I’m going to be on the eclipseofthecentury.com tour. There are still seats available.

Fraser: That would be fun. I’d love to see an eclipse. I’ve never seen a total solar eclipse.

]]> http://www.astronomycast.com/astronomy/observing-astronomy/ep-118-sky-surveys/feed/ 5 http://www.astronomycast.com/astronomy/stars/ep-108-the-life-of-the-sun/ http://www.astronomycast.com/astronomy/stars/ep-108-the-life-of-the-sun/#comments Tue, 30 Sep 2008 20:02:18 +0000 Astronomy Cast http://www.astronomycast.com/?p=384
We've talked about the Sun before, but this time we're going to look at the entire life cycle of the Sun, and all the stages it's going to go through: solar nebula, protostar, main sequence, red giant, white dwarf, and more. Want to know what the future holds for the Sun, get ready for the grim details.

Ep. 108: The Life of the Sun

Overviews:

• Stellar Life Cycle flow Chart
• The Life and Death of Stars
• The Natures of the Stars
• Stellar Evolution
• Life Cycle of a Star
• The Life of a Star
• Everything you need to know about the sun from Universe Today's Guide to Space

And the details…

• Protostars – from Astrophysics Spectator
• Protostars – from Wiki
• Hayashi Track – from Internet Encyclopedia of Science
• Mass-Luminosity Diagram — from Courtney Seligman
• Paper on the sun's activity for the past 8,000 years – from Max Planck Society
• Jupiter gives off more heat than it gets from the sun
• Accretion disk -- from Internet Encyclopedia of Science
• Paper on magnetic fields of stars – from IAU
• Main sequence stars — from CSIRO
• Table of main sequence star data
• Nuclear Fusion of Stars -- from Astrophysics Spectator
• Post-Main Sequence Stars and Helium Flash
• Gravitational Collapse of Stars — Astrophysics Spectator
• Horizontal Branch Stars
• Variable Stars – from Chandra's website
• Variable Stars — see Episode 22
• Check out American Association of Variable Star Observers
• Mira Variable stars
• Pauli Exclusion Principle
• Diamonds in the sky — White Dwarf stars
• Globular Clusters
• Will the Earth Survive When the Sun Becomes a Red Giant? – Universe Today

A few papers on star formation:

• Protostar Formation in the Early Universe
• Properties of Protostars in the Elephant Trunk Globule
• Problems of Star Formation Theories and Prospects of Submillimeter Observations
• Evolution of Massive Protostars with High Accretion Rates

Misc:

• Expansion Rate of the Universe
• Should you drink red wine?
• World Cast, Oct. 4 — starring Dr. Pamela Gay! "The Origins of the Universe" Live webcast, 20:00 UT

Download the transcript

Transcript: The Life of the Sun

This transcript is not an exact match to the audio file.  It has been edited for clarity.  Transcription and editing by Cindy Leonard.