Comments on: Ep. 129: Interferometry

By: michael cassidy

michael cassidy — Fri, 27 Mar 2009 12:29:06 +0000

It is one of the shows I need to listen to 4-5 times.
AND I have now printed out a bunch wiki articles on interferometry.

By: Claude

Claude — Tue, 24 Mar 2009 22:26:04 +0000

Never say never, but interferometry is quite challenging! Before we start thinking about linking our 16" Dobs together, we'll need to deal with seeing. Currently, the resolution limit of even relatively small backyard telescopes is due to the atmosphere not aperture. Adaptive optics will much more likely become a common astronomical appliance long before we even start to dream about trying to link together separate telescopes.

By: Royden

Royden — Tue, 24 Mar 2009 02:02:25 +0000

So when will amateur astronomers be able to do this? Now that astrophotography is available to amateurs using ccd's, when will we see star parties coming together via the Internet to do some amazing observations? I'm just guessing here, but I'm sure this could be a reality, and quite handy for observing near earth objects. Am I wrong?

By: Claude

Claude — Thu, 19 Mar 2009 20:17:03 +0000

This episode seemed to differentiate between interferometers such as the Very Large Telescope (VLT) and telescopes like the Giant Magellan Telescope (GMT). I must point out that GMT actually will be an interferometer. It will use seven 8.4-m mirrors working interferometrically to give the resolving power of a single 24.5-m mirror! The difference between the GMT design and more "conventional" interferometers is that all seven mirrors will be carried together on the same mounting. The resulting mount will necessarily be huge and difficult to engineer but means that the mirrors will track together across the sky and the path difference, mirror-to-mirror, will only be due to inaccuracies and flexure in the mounting not due to the distance between mirrors. The delay lines that compensate for this small path difference between mirrors can thus be very short – only centimeters instead of the many meters needed for the VLT and similar separated interferometers.

Cheers,
Claude

By: Richard Hubbard

Richard Hubbard — Wed, 18 Mar 2009 14:13:49 +0000

I'm working my way through old podcasts, so I haven't reached this one yet, but the title caught my eye.

Interferometry is an amazing technique in many different situations. During my senior year in college, my thesis project was to help the department chair with an interferometer for sound.
At first, someone might say "huh"? But here was the interesting part. The speed of sound through a gas depends on the Ideal Gas constant. Unfortunately, the Ideal Gas constant, until that time had only been measured using one technique, measuring volumes of gasses at different temperatures and pressures, and calculating it. This works, but it is almost circular reasoning.
So, the professor figured that if he could measure the speed of sound accurately enough, he could calculate the gas constant using a completely different method. If it was the same as what was already known to be the gas constant, then it was confirmed independently. Which would be nice, but rather dull. If it was different, then there would be a clue that there was a whole lot we didn't know about gasses that needed to be explored.
Unfortunately, we ended up demonstrating that the Ideal Gas Constant really was constant. Nice to know, but rather dull!

I look forward to listening to this episode!