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Questions Show: Different Fields of Astronomy, Our Sibling Stars, and Hidden Lagrange Points

Pleiades Star Cluster.

Pleiades Star Cluster.

This week we find out the difference between an astronomer, an astrophysicist, and a cosmologist, the search for the stars that shared our nebula, hidden objects in Lagrange points, and much more..

If you’ve got a question for the Astronomy Cast team, please email it in to and we’ll try to tackle it for a future show. Please include your location and a way to pronounce your name.

  • Different Fields of Astronomy, Our Sibling Stars, and Hidden Lagrange Points
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  • Shownotes

    What’s the difference between an astronomer, astrophysicist, and a cosmologist?

    Can we find stars that came from the same nebula as our sun?

    Could there be a hidden body at L3?

    • Ep. 76: Lagrange Points
    • Missions to the sun:  Ulysses, SOHO

    What can we expect to see with the next generation of space telescopes?

    Is energy getting lost with the expansion of the universe?

    When stars go supernova, how big are the particles that are left over?

    How do we measure things created by the LHC?

    Can we see the center of the galaxy with our eyes?

    Transcript: Different Fields of Astronomy, Our Sibling Stars, and Hidden Lagrange Points

    Download the transcript

    Fraser Cain: Okay. Here we go. This week we find out the difference between an Astronomer, an Astrophysicist and a Cosmologist. Is that a joke?

    Dr. Pamela Gay: It really does sound like one.

    Fraser: The search for stars that shared our Nebula and hidden objects in Lagrange points and many more. Now, if you have a question for the AstronomyCast team, please e-mail it in to, and we’ll try to tackle it for a future show. Please include your location and a way to pronounce your name.

    Alright, let’s get on with the first question. This comes from Heather Roy in Tampa, Florida. “What is the difference between an Astronomer, an Astrophysicist and a Cosmologist? Which one are you? And why?” Alright, Pamela, what is the difference?

    Pamela: Well, classically the difference is Astronomers are the people who look up and take pictures, who classify things based on images and morphology. And Astrophysicists are the folks who go through and define “well, based on this set of forces, based on this set of chemistry, based on this set of quantum mechanics, and this set of relativity, here is why we get what it is that we see when we take these amazing images.” When we take these amazing spectra, they are the ones who define the “whys,” whereas the Astronomers are the ones who define the “whats.”

    Then we went on and realized, well the whole Universe is evolving and that takes Physics to a whole new level. So Cosmologists are the people who step beyond studying just the Stars and Galaxies to study basically how everything large scale structure, how everything out there the Cosmology of the Universe in terms of the Cosmos evolving is changing with time.

    Now, as to which one I am, well it depends on where you want to get all technical on things. My undergraduate degree from Michigan State University is actually in Astrophysics. But I have to admit that I’ve tended much more to be a let’s take pictures, look for trends, and try to understand based on other people’s theories versus coming up with theories on my own.

    So I am much more of an Astronomer. I have done work on the evolution of Galaxies and there are those out there who would call me an Observational Cosmologist, but really I am an Astronomer.

    Fraser: Right. So, let me just throw some jobs at you and you tell me which one would be doing this okay.

    Pamela: Okay.

    Fraser: So, coming up with the new theories for the Big Bang.

    Pamela: Cosmologist.

    Fraser: Counting the number of Galaxies in our local region.

    Pamela: Astronomer.

    Fraser: Working out the magnetic forces around a super massive black hole.

    Pamela: Astrophysicist.

    Fraser: Okay. I think I understand. Alright, let’s move on. So the next question comes from Eric Burns. “Since our Sun came from a Nebula, is it safe to assume that the same Nebula also gave birth to other Stars? And if so, can we find those brother/sister Stars?”

    So, you know, we look at a place like the Orion Nebula and we know that that’s what our Sun was born from. You know, 4 ½ billion years ago. So, since there are lots of Stars forming within the Orion Nebula, did we have lots of Stars forming around us when our Sun formed?

    Pamela: As near as we know, all Stars formed in groups. And as we look out around in our Milky Way Galaxy we see open clusters of Stars at various ages. In fact right now this is the perfect time of year to go outside look up and sort of see the history of Star formation. I have an entire entry on my blog,, all about this.

    So you can go out and look at the Constellation of Orion and there’s the Orion star forming region. That’s a very young system measured in not very many millions of years old, there’s still amazing OB Stars, the hottest largest Stars out there. There are still Stars forming today.

    Then you can look at the Pleiades System the Seven Sisters, it looks kind of like the Subaru symbol on the back of a car that’s actually modeled after the Pleiades Constellation. Subaru is what they call it in Japan. And this is something that’s older. It’s blown out most of its gas and dust and most of the Star, well in fact all of the Star formation, has stopped. But the Stars are still close together. You can still look up and see this is a tight little cluster of Stars.

    Then if you look over at Taurus and here you probably need to get some binoculars, if you look around Taurus with binoculars you will see that the density of Stars is much higher than in other regions of the Sky. This is because there’s the Heiades cluster in Taurus. It’s a much older system. Here the blue Stars have begun to die.

    The Star system has begun to spread itself out as it orbits around the Milky Way Galaxy. As Star systems orbit, the ones that are closer to the Sun go a little bit faster. Those that are further go a little bit slower.

    Over time the system basically shreds itself. Over several orbits you can no longer find the Stars that all were born together. Our own Sun has gone around the Galaxy more than once and so nowadays with any reasonable survey we can’t find their siblings.

    Really the only way to do it would be to do a careful kinematics study and very detailed measurements of all the isotopic ratios. Even then there are slight variations from Star to Star within a cluster. Who’s to say there wasn’t another cluster of a similar age with a similar composition?

    Fraser: So, the bottom line is that the Stars are just too spread out now for us to be able to find them.

    Pamela: Yeah, it’s kind of sad, but that’s the way it worked.

    Fraser: Alright, moving on. This comes from Daniel Kim from London, England. “I was just listening to your Lagrange Point episode and was curious about L3. Is it possible that there is a hidden body of mass on L3?” That’s the one on the other side of the Sun that we cannot detect and which we will never see. I believe there was a terrible science fiction series about this which I won’t even say the name. [Laughter]

    So, L3, this is, we have a whole episode on the Lagrange Points. These are the stable points in the Solar System I guess where in any gravitational interaction where things can remain either stable or unstable and not require much energy to keep them in that position.

    The L3 is the one that’s on the opposite side of the Sun that is, as I remember, is a little further away from the Sun than we are on the opposite side. So, is it possible that there’s something hiding that’s in perfect balance with us on the other side of the Sun?

    Pamela: No.

    Fraser: No, it’s not possible? Why is it not possible?

    Pamela: Well, first of all we would have noticed its gravitational perturbations on other objects in the Solar System. We have very carefully been watching where all the Planets are at, where they’re going. We know about the Asteroids, we know about the Comets, and to account for all the slight variations and motion, we have to know all the Planets are there.

    Now, not only can we say no its gravity would have mucked things up and our calculations would have gotten thrown off by its gravity not being accounted for, but we have also sort have gone and looked.

    There are missions studying the Sun that have passed over the poles of the Sun and while out there they would have kind of noticed another Planet on the other side. We’ve sent things to Mars that have had the ability to look around at the other side of the Solar System.

    Somewhere along the line we would have noticed this other Planet. It hasn’t appeared either in our gravitational motions and it hasn’t appeared in images. So, there’s just not anything there.

    Fraser: But isn’t the L3 one of the ones that is unstable?

    Pamela: Yeah.

    Fraser: Yeah. So, I mean, you can, if you have like a spaceship with rockets you can maintain a position at L3 using your rockets very carefully and it doesn’t require enormous amounts of energy. But if you stop trying to keep yourself in that position, then you slowly start to drift out of that point.

    It’s like the top of a hill is a way you described it, right? It’s not the bottom of a hill, where you know, the bottom of a bowl where you keep rolling back in. It’s the opposite; it’s the top of a hill. You could stay right at the very top.

    But if you get off the top then you drop out of that position quite easily and quickly and then it’s very hard to get back up into it. So even if there was something there, it’s not a stable place for it to be so it would very quickly become visible again. Alright, well I think that’s that. So no hidden object.

    Alright. The next question comes from Richard Summers and Richard wants to know: “What might the next generation of super telescopes or space telescopes truly expect to see?”

    So, I guess the next generation, and we did a show on this, the rise of the super telescopes so we go into detail, but you know, with the James Webb with the terrestrial planet finder…

    Pamela: Overwhelmingly large.

    Fraser: Overwhelmingly, the ridiculously large telescope, what kinds of things should they be able to see?

    Pamela: Well, this is where we’re going to start to be able to detect the first Galaxies forming and start to see them as just more than four pixel smudges on bad images. We’re going to actually start to be able to study how Galaxies build up piece by piece in the early moments of our Universe. We’re going to be able to look out and see Planets more than an occasionally.

    We finally did it! Fraser was right when he said we detected a Planet separate from its Star via its light in the next few years. He should have said the next few months.

    Fraser: Next few months, next few days.

    Pamela: Exactly. But we’ll be able to regularly start to see Planets around other Stars. These amazingly faint Brown Dwarfs that have recently cropped up that if you put them in the position of the Sun would be fainter than the full Moon.

    We’ll be able to actually count these things that are probably one of the most prevalent objects in the Galaxy. We’ll actually be able to go out and say ah, I see them everywhere.

    So we’re going to be able to see the small things, the faint things, and the faraway things and really start to get a grasp on how do Galaxies build? What is the population of the faintest Stars? What are Planets like around other Stars?

    Fraser: So, I think that is going to be one of the major next steps. I mean, we’ve talked about this before as well. It is the most important scientific question. Is there life elsewhere in the Universe?

    So, the first step to that is to be able to detect life on other Planets, the next generation. Not the James Webb, but if the Terrestrial Planet Finder or Darwin do get completed, you’ll have a telescope that can sense the presence of well not life exactly, but I guess the gasses in the Atmosphere that would say if there is life there.

    Pamela: And James Webb WILL get us at the building of Galaxies which is cool too. Just not as life shattering.

    Fraser: Yeah. So that’s the main one. And then, everything in between, you’re going to be able to see closer in on the Excretion disks around Black Holes. You’re going to be able to see with more precision the structure of distant Galaxies.

    Pamela: The structure of Planetary Nebula. I mean these are one of the coolest objects in our own Galaxy. Especially where we have Planetary Nebula formed in binary systems that look like someone had great fun with a Spirograph. We’re going to be able to study the death of Stars in detail.

    Fraser: So, I mean, you can just imagine more better on every single aspect of Astronomy. You’re going to just be able to push the limit in every direction. But I think the big prize that’s going to come out of this, I think as Pamela said; you’re going to be able to look right back to the edge of the observable Universe.

    When the next generation telescopes come out, we’re going to be able to see right to the limits of what is possible to see in terms of distance and the kinds of Galaxies and building blocks that are starting to get formed which is awesome.

    Alright. So the next question comes from Freddy Luzenac from Honolulu, Hawaii. “It’s my understanding that light from the red end of the spectrum is less energetic than from the blue end of the spectrum. So the question is: If a Photon starts its journey from a distant Galaxy as an Ultraviolet Photon and travels across the Universe to reach us as a less energetic Infrared Photon, then where did that lost energy go? And is it possible that it could get red shifted to such large amount that it loses all of its energy and ceases to be?”

    So, I guess the question Freddy is getting at is the expansion of the Universe after the Big Bang, with the ongoing expansion and acceleration thanks to Dark Energy is stretching out the wavelengths of light it’s attempting to travel so when maybe the Photon started out in the early Universe they were ultraviolet, by the time they reached us now they have been stretched right out to be say infrared, or even microwave. Is any energy getting lost?

    Pamela: No. It’s just going to be spread out. The way to think about it is if you have a really hot rock (for lack of a better object) and you put it in a little tiny well insulated box, you have that heat energy confined into a small space and it stays hot.

    Now if you take that same rock worth of energy and you put it in a larger box and you allow that heat energy to evenly distribute itself throughout the box it’s going to cool and it’s just a matter that you spread the heat energy over a larger volume.

    Well, as you spread the heat energy over a larger and larger volume, the temperature in any one given place is lower but the total amount of heat energy contained in the entire box is exactly the same. You’re just spreading it out more and so the temperature is lower but the amount of energy contained in that volume stays constant.

    Fraser: Okay. I like your analogies better than mine. I was going to take a piece of gum and stretch it out and say where’s that gum going?

    Pamela: [Laughter] You have kids.

    Fraser: Right. Okay. So then I guess the question then can, so it’s not losing its energy so then I guess the second question is can it lose all its energy cease to be? If it’s never losing its energy it never ceases to be. So what is the limit then of how far a Photon can go?

    Pamela: It’s just going to keep stretching with the Universe. It’s eventually going to reach the point that we can’t perceive it. Once you start getting wavelengths that are bigger than we can build antennas that can capture reasonable fraction of the wavelength, we’re not going to see it. You can imagine Solar System sized wavelengths eventually.

    Fraser: Right. There’s no way you will be able to detect those going past.

    Pamela: Right. And the energy in them is so low. But that’s what happens. The energy just spreads out more and more and more.

    Fraser: But the energy is still there. The Photon is always there. It’s just trying to fill up a larger and larger space of volume of the Universe and so it’s harder to detect.

    Pamela: And this is part of where energy depth comes in is all the energy we have is eventually going to get spread out so much that really the Universe is absolute zero.

    Fraser: Yeah. Alright, so this question comes from Dr. Gavin Kushannan. (Should have shown us how to pronounce your name.) “When Stars go Super Nova how big are the particles that are left over, particularly the heavier elements?”

    So, I guess I can imagine, right, in a Super Nova in a fraction of a second, all of the Heavy Elements are produced from the Gold on the ring on my finger to the Platinum in my car that are all generated in an instant do you get like big chunks of Gold flying through space?

    Pamela: No, and this is where one of the things that we don’t talk about often enough is the way these Heavy Elements are getting made in Super Nova isn’t generally from smashing multiple Atoms together but rather it’s from the Atoms in the outer layer of the former Star getting nailed with Neutrons at a really high rate and forms a beta decay. The Neutrons are converting to Protons and you’re getting Electrons flung off and all sorts of stuff going on.

    It’s from this flux of Neutrons that we’re building the heavier Elements and not from smashing Atoms together. Densities are still low enough that you don’t end up with basically a nugget of Gold flying away from a Super Nova. That would be really cool, but it just doesn’t happen.

    Fraser: But how do you explain veins of Gold? You know, that things will end up in the same kind of spot on Earth for example?

    Pamela: Well that’s more differentiation of a hot body. You take a rock, heat it up, spin it up and the stuff inside is going to differentiate in part by density.

    Think about it if you have a container of water and leaves and blueberries if you jostle the container you can usually get the leaves and nasty stuff to float to the surface on top of the blueberries.

    The blueberries are trying to float too, but if you jostle it enough it’s a good way to get the leaves to rise to the surface so you can scrape them off to be left with the blueberries.

    Fraser: So you can almost imagine then a vein of Gold being maybe one of the chunks that came together to form the Earth had already differentiated to the point that the Gold was sort of separated from that glob of the Earth and that’s where it was.

    Pamela: And it made it easy for us to find it to mine it and make wedding bands.

    Fraser: Right after the Super Nova a spray of Gold Atoms.

    Pamela: Yeah.

    Fraser: Alright. Let’s move on. This next question comes from Jonathan. “How do we measure the things produced by the large Hadron Collider when they are smaller than anything we can manipulate?”

    Small Electrons, Protons, etc., and I guess that’s the question, right. We’re smashing two Protons together; we’re getting microscopic particles being created and decaying in fractions of a second and hitting into other stuff. So how do we know these things are happening?

    Pamela: Luckily, they tend to give off flashes of light at different stages in their decay process. So when they build detectors they do a number of different things. They will essentially weave spider webs of fiber optics that when a high energy particle passes through one of the fibers it scintillates. It gives off a bit of light that runs down the fiber optic and is detected with a photomultiplier, a very, very sensitive light detector at the end of the fiber.

    We also have arrays of photomultipliers, arrays of panels of scintillates. It all depends on what exactly they are trying to detect what set of instrumentation they are using. But in general what they are actually looking for is the little flashes of light that are related with the decays of the different particles that are formed and then we look to see where those flashes are given off.

    Fraser: Right. So, we’re not actually taking pictures of Quarks or Higgs-Bosons hopefully. We’re seeing the little flashes of light in very specific wavelengths as they decay, as they give off various kinds of energy as part of their process. That’s what we’re detecting. Then they are saying if we see this light at this wavelength and that light at that wavelength then we know that had to be a Quark decaying and therefore Quarks are created.

    Pamela: And we’re keeping track of the where’s and when’s these flashes are occurring. There is an interaction over here, this many fractions of a second afterwards that meant that it had to be going at this velocity which meant that it had to have that mass. By keeping track of the where’s, when’s and the energies, we can start to figure out momentums, we can start to figure out masses, and all of this allows us to figure out well, what was it in there?

    Fraser: Right. So it’s quite some detective work. Alright, so the next question comes from David Cooper. “Can we see through telescopes or binoculars or even our eyes, the center of the Galaxy?”

    So, can I go outside and look up and see the center of the Milky Way with my eyes?

    Pamela: No, your eyes work in the wrong wavelengths.

    Fraser: Can I see a region of Sky where the center of the Milky Way is?

    Pamela: Yes. That’s called Sagittarius.

    Fraser: That’s Sagittarius.

    Pamela: Yes, wait for summer. It works better then.

    Fraser: Right, right. Sagittarius is the one that looks like a teapot.

    Pamela: And from the northern hemisphere it’s very low in the southern Sky and it’s actually below the Equator in the south. But, that’s where the center of the Galaxy is located is in the direction of Sagittarius. If you actually want to see the center of the Galaxy you can do it in the infrared.

    This is where we’ve gotten some really amazing images of Stars actually orbiting the Black Hole of the center of our Galaxy. We can watch them do it on orbits that get them within basically Pluto’s distance from the Sun of this Black Hole. It’s really, really cool.

    Fraser: Right, so the problem is that the center of the Milky Way is surrounded by dust and that dust blocks the light coming from the center of the Stars that are behind it. So a regular telescope or binoculars or your eyes, although you can see the region, you could point and say right there, that is the center of the Milky Way, you couldn’t actually see the Stars that are in there just because they’re being blocked. Switch to infrared you see nicely through that dust and you can actually see the Stars orbiting the Super Massive Black Hole, which is crazy.

    Pamela: Yeah, and they’re doing it in basically order of 10 years and our outer Planets go slower than that and…

    Fraser: And at the time we’re recording this there was an amazing new update to the Super Massive Black Hole tracking those Stars. They released a whole new set of data about all of the Stars that orbit that Super Massive Black Hole and to really confirm that yes, indeed, we do have a Super Massive Black Hole at the center of the Milky Way.

    Pamela: And this is all work that was started by Andrea Getz who was the one who figured out the right imaging techniques to use so hats off to her for doing a long term really good body of work.

    Fraser: And helping to pin down one of the most, the biggest new discovery within the last couple of decades is these Super Massive Black Holes.

    Alright, so the next question comes from Karen. “Does a full Moon appear in both hemispheres at the same time?” So if I’m in Canada and I’m looking at a full Moon, and you’re in Australia and you’re looking at the Moon, are we seeing the same phase at the same time?

    Pamela: You’re kind of stretching it between Canada and Australia because I can’t remember what the time differences between those two are. But, if you wanted to between North America and South America yes, very much yes.

    Fraser: Right.

    Pamela: Between Vancouver and Australia it depends on where in the Sky it is because it might just be set in one place and just rising in the other place.

    Fraser: Okay. In North and South America if I and my South American colleague are looking in the Sky we’re going to see the Moon have the same phase. I could call him and say “it’s a full Moon,” and he’d say “yep, I agree. We’re seeing a full Moon.”

    Pamela: Yes, that’s totally true.

    Fraser: Right, so why is that?

    Pamela: Well it’s basically they’re just balls and as long as you’re moving north south along the same line on the Planet, where the Moon is relative to your horizon is going to change but how the Sun is illuminating the Moon isn’t going to change.

    The distances are so vast between us and the Moon and both the Moon and us and to the Sun that by moving yourself around on the planet Earth, you’re not going to get a discernable change in phase. You’re just going to move it around in the Sky. So call up your friend and enjoy the full Moon together.

    Fraser: And that’s why, for example, Solar Eclipses only happen in very specific part of the Earth.

    Pamela: Yeah, it’s about 170 mile wide swath and if you want to see one I’m going to go see one this summer.

    Fraser: I know, I know.


    Fraser: But for a Lunar Eclipse, everyone on Earth who can see the Moon sees the eclipse. So in many cases, if you can’t see the Moon it’s only because it hasn’t risen or it has already set. But otherwise, if you can see the Moon, you can see the eclipse.

    Pamela: Half the Planet at any given moment can see whatever part of the Moon happens to be illuminated.

    Fraser: Right. Alright, and here’s our last question and this is sort of a fanciful, out-there one, from Patrick Berry. “Just a quick question, do you think there is any possibility that Mercury could be the long lost satellite of Venus?”

    So, Venus, does Venus have any moons?

    Pamela: No, actually it doesn’t.

    Fraser: No moons for Venus.

    Pamela: Yeah, it’s 0012 in terms of how many moons the Planets have.

    Fraser: Yeah. No moons for Mercury, no moons for Venus. I know that Mercury size-wise is smaller than Ganymede and smaller than Titan, so if it was orbiting a Planet it would be third largest Moon in the Solar System.

    So, it’s the right size. It’s a little bigger than the Earth’s Moon, but still it’s sort of in the same ballpark, so could it be a satellite of Venus?

    Pamela: Well, kinematically there is no reason to believe that’s what happened. Both Venus and Mercury are in nice happy orbits. Mercury’s is not the roundest in the Solar System. It is actually fairly an ellipsoid in shape, but there’s no reason to think that it could have come from Venus.

    Now we could nominally do some testing if we could go and grab samples from the two objects. For instance, we’re sure that the Moon and Earth formed in the same part of the Solar System based on some of the isotopic ratios that indicate that they were in a similar place in the Solar Nebula when they formed.

    If we could do sample returns to these two extremely hot objects we might be able to answer that question. But there’s absolutely no reason to believe that Mercury used to be a moon of Venus based on its current orbits.

    Fraser: Right. So even though it’s sort of the right size, Venus’ orbit is very circular; Mercury’s orbit is somewhat eccentric, but not.

    Pamela: It’s not terrible.

    Fraser: Not Pluto eccentric.

    Pamela: Yeah.

    Fraser: And so it is still orbiting the Sun and it would be some pretty magic billiards to get Mercury from going around Venus to getting into a nice roughly circular orbit around the Sun. That would be pretty, that would require a lot of three body interactions, right?

    Pamela: [Laughter] Yes. And we know that Venus has probably had a fairly traumatic history, but Mercury seems perfectly fine.

    Fraser: That’s not to say that Venus didn’t necessarily have a moon in the ancient past. It could have easily had a satellite and it could have been flung off or could have crashed into the Planet.

    Pamela: Yeah, we have no way of guessing it. The history of the earliest points in the Solar System, but right now we just don’t have any evidence of anything happening like that. You can’t follow a lack of evidence to a cool conclusion no matter how much you may want to.

    Fraser: Right. So we’ll wait for the actual data to be gathered. We’ll wait for some spacecraft to go and really do the isotopic work on the surface of Venus.

    Pamela: And I’m not going to be involved in building a robot that goes and does sample return from Venus.

    Fraser: Right. That would be hard.

    Pamela: [Laughter]

    Fraser: Hard. I can’t even imagine trying to launch back up into the atmosphere. I can’t even imagine. I don’t think it would be within our…

    Pamela: Yeah. Swimming fins.

    Fraser: Swim back up. So anyway, very complicated, very difficult. That might be one of the hardest questions to answer. Still, it’s a cool idea. I think parts of it totally make sense and parts are like “yikes.”

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