View Full Version : Episode 41: The Rise of the Supertelescopes

2007-Jun-18, 03:00 PM
The last decade has been the golden age of astronomy, with new observatories and space telescopes pushing out our understanding of the Universe. We can see billions of light years away, watch dynamic events unfold in almost real-time, and see into every corner of the electromagnetic spectrum. Just you wait: things will only get better. Here come the supertelescopes!

Read the full blog entry (http://www.astronomycast.com/observatories/episode-41-the-rise-of-the-supertelescopes/)

2007-Jun-18, 09:28 PM
Hi Pamela and Fraser;

I just wanted to clarify something; In the show you say that the Keck telescopes use single cast mirrors. The Keck observatory website says:

"At the heart of each Keck Telescope is a revolutionary primary mirror. Ten meters in diameter, the mirror is composed of 36 hexagonal segments that work in concert as a single piece of reflective glass."

2007-Jun-19, 03:01 AM
It is an amazing instrument.
A friend of mine did the coatings on it.
Imagine if we had the Keck in space !!!!!!!!
Patience.......patience .
Best regards, Dan

2007-Jun-21, 05:24 PM
And, the South African Large Telescope (SALT) has a single (spherical) 11 meter mirror(!). There are restrictions on what it can do. Try and wrap your head around this description:

SALT has an 11m diameter spherical primary mirror with an optical axis tilted to 37 degrees from the vertical. It can rotate through 540 degrees in azimuth. Positioned ~13m above the mirror, is a tracker and an optical payload, looking down at the mirror. The tracker moves across the mirror on a virtual spherical focus surface, allowing sky-objects to be "followed" as the earth rotates, without adjusting the azimuth angle for a period of up to two hours. This gives the telescope an annulus-shaped observing area in the sky, 12 degrees wide between declination angles of approximately -75 degrees and +10 degrees.

The expensive thing about telescopes is tracking. The 'mount' is more expensive than the mirror. That's true for a back yard imaging scope. It's true for the Mt. Polomar "big eye". It's true for the HST (launch costs). So, the SALT does some things to make the mount cheaper at the cost of reduced viewing.

The podcast didn't talk about interferometry. There's the Mt Wilson experiment. There's the Keck. There's the VLT.

For space based infrared, the idea that Spitzer has a finite supply of helium for cooling wasn't mentioned. The scope will be functional, but with reduced sensitiviy when it runs out. But what about the James Webb?

Then, there's the HST. It has done infrared and ultraviolet. The fine guidance sensors can be used for science, not just guidance. Also astrometry. But the side to side wobble of a brown dwarf was measured - side to side from an orbiting object. Very cool. Several whole shows could be done on the HST and it's various instruments. Probably true for some of the other big instruments - Keck, VLT, the Hale. In fact, my astronomy club just had an hour talk given about the Hale.

2007-Jul-02, 07:00 AM
I was fortunate enough to be at the Sewell Mirror Lab on the day that the glass melted for the first off-axis segment for the GMT. VERY cool process and incredible technology to make the mirror both strong and light. They put ceramic hexagonal "rods" in the oven and put he raw glass (in block form) on top of it. They then rotate the oven at the correct speed while heating the glass. The glass melts and forms a shape that is very close to the final shape needed. After the glass cools (which takes months), they remove the rods. They then do their final finishing of the mirror. We also got to see the mirror for the second halve of the large binocular telescope undergoing final testing.

Very cool all around. The main problem is that I couldn't figure out how to get an 8m mirror in my mini-van.

2007-Jul-05, 02:51 AM
Don't forget the SALT telescope is very closely based on the Design of the Hobby-Ebberly Telescope at McDonald Observatory. Since Pamela is a U of Texas alum, you could get in trouble for this :)

I have had the good fortune of visiting several of the big telescopes including the Hobby-Ebberly Telescope, Keck, and Gemini North (as part of my job if you can believe that!) And I have observed with the Green Bank Telescope.

I would like to hear a show on the developments in radio astronomy sometime...VLBA, LOFAR, ALMA and the like.