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Wow… those are some big telescopes! July 18, 2009

Posted by pjhsci in Astronomy, Observatory, telescopes.
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Matthew Sanders has his blog at:   http://pjhsci.wordpress.com/

You know, most people think that the Hubble Space Telescope with its 2.4 meter mirror is the best window into the universe because it resides in orbit, has no atmosphere to mess with the view, and above all, it is almost always the only telescope that you hear about through regular media venues.  This will change within the decade.  There is a new breed of telescopes that are Earth-based that can deliver images ten times sharper than Hubble is capable of.  In the works are reflectors that will provide images up to 100 times sharper than that!

How we adjust for our shortcomings, being here on Earth and all…

Most of the largest scopes today use reflectors measuring 8-10 meters across that may be segmented into many smaller mirrors such as the Keck system of Hawaii.  Keck II Mirror showing segmentationThese scopes benefit not only from the fact that the mirrors can gather a large amount of light, but also the use of adaptive optics systems. (The AO system in the photo of Keck II is at the top of the photo partially housed on the frame skeleton along the right-hand side.)  These systems are what allow Earth-based telescopes to compensate for one of the plagues of astronomers on Earth:  the atmosphere,  more specifically, the turbulence within the atmosphere.  That turbulence is what makes the stars appear to twinkle.  AO systems reduce, if not eliminate, most of that issue.  The simplified version of how AO systems is rather neat.  A laser is fired from the telescope into a thin layer of sodium atoms that exists in the atmosphere, causing them to glow.  This glow is monitored by the AO system to adjust for the atmospheric interference more than 1000 times per second.  This technology turns distant stars from pretty, fuzzy-edged smears to clear, tiny points of light.  Without AO, astronomers could differentiate between objects that were 1/3600th (1 arc second) of a degree apart.  Now, using AO on current scopes like Keck, astronomers can identify multiple objects within that single arc second!

Wait, only an 8.4 meter mirror?  What is so special about that?!

Courtesy www.lsst.org/News/ 0501/050111.shtml
The LSST will provide a generous field of view to explore. Courtesy http://www.lsst.org/News/ 0501/050111.shtml

In August of 2008, under the football stadium at the University of Arizona, a spinning furnace cast the 8.4 meter mirror that is going to be the eye of the Large Synoptic Survey Telescope.  The LSST will be unique, not in the size of the mirror, but in the field of view it should provide.  Conventional scopes have a field of view of around 0.5° per side.  The LSST will provide astronomers a field of view that is 10° per side.  That means that the LSST can take images of the entire visible night sky over the course of a few days rather than months or years.  It will be located on a mountaintop in Cerro Pachón, Chile.  This will allow astronomers to observe objects and events at distances over 10 billion light years!  The ability to record the entire sky repeatedly and quickly will give astronomers the chance to build a motion picture of sorts of short-term events that are missed using conventional telescopes.  Over the course of many cycles, new near-Earth asteroids could be located, flares on dim stars could be identified, and perhaps some of the mysteries of dark matter and energy could be brought into clearer focus.  Innovative telescopes like the LSST could be the key to unlocking those riddles that drive astrophysicists bonkers with uncertainty.

Okay, how big are we talking here?

If one 8.4 meter mirror is good, why not use two?  The Large Binocular telescope on Mt. Graham in Arizona boasts two 8.4 meter mirrors that produce an effective light gathering ability of an 11.8 meter telescope.  With some of the new adaptive optics enhancements coming down the pipe, it is hoped that the LBT will have the effective ability of a 23 meter scope in a smaller package.
If one 8.4 meter mirror is good, why not use two? The Large Binocular telescope on Mt. Graham in Arizona boasts two 8.4 meter mirrors that produce an effective light gathering ability of an 11.8 meter telescope. With some of the new adaptive optics enhancements coming down the pipe, it is hoped that the LBT will have the effective ability of a 23 meter scope in a much smaller package.

There are two schools of thought on this matter:  single reflector or multiple reflectors.  The Large Binocular Telescope in Arizona uses a tandem mirror (Keck I and Keck II can be used in tandem, as well) to provide an image greater than the sum of its parts. (see sidebar)  These arrangements can be constructed in smaller spaces where area is at a premium.  A tandem system takes images from both mirrors and uses computer programs to combine the images, adjusts them with the AO system and produces a composite image.  Other multiple reflector systems are on the slate as well.  In 2018, it is projected that the Giant Magellan Telescope will be functional in Chile.  This composite telescope will utilize not two, but seven 8.4 meter mirrors to produce an image!  The Very Large Telescope array will use a total of eight reflecting units when fully operational.  There will be four 8.2 meter stationary units and four 1.8 meter moveable units to compile images.

This is really interesting technology, but really, just how large a single reflector telescope are astronomers trying to construct?  The Thirty Meter Telescope is to be located in either Chile or Hawaii and scheduled to be online in 2018, but that is small potatoes compared to another monster slated for 2018.

This image portrays the proposed European Extremely Large Telescope with its 42 meter reflector.  This giant is actually a scaled down version of the budget-crippled Overwhelmingly Large Telescope that was to utilize a 100 meter reflector!
This image portrays the proposed European Extremely Large Telescope with its 42 meter reflector. This leviathan is actually a scaled down version of the budget-crippled Overwhelmingly Large Telescope that was to utilize a 100 meter reflector!

The Extremely Large Telescope is just that; an extremely large telescope!  This 5500-ton reflector system will be housed in an observatory 80 meters tall and 100 meters in diameter.  The mirror will be a staggering 42 meters across… yes, 42 meters! Imagine the distance that our puny human optics will be able to penetrate into space with this behemoth as our tool!  What new worlds could we discover?  What origins of the universe could we unveil?  Just imagine what we will be able to see…

LBT Photo – www.kosmologs.de/
ELT Photo – www.spacedaily.com/

Information gathered from:

National Geographic, June 2009

European Space Organization

Bill Arnett’s Nine Planets.org

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