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Hubble vs. Webb - How Far Back Will They See?
Roland Piquepaille writes "According to Forbes, reporting in "Peering Back At The Universe's Past," space telescopes are really acting as time machines. They can watch objects which are so far from us that light has taken billions of years before reaching their mirrors. The Hubble telescope is able to look at events that took place 13.3 billion light-years ago. But the James E. Webb space telescope, currently under construction, and scheduled to be launched in 2011, will be able to see even further and catch phenomena which happened 13.5 billion light-years ago. The astronomers think the Webb telescope might even be able to see up to 13.7 billion light-years ago, when our universe was just 200 or 300 million years old. We are used to see fantastic images from Hubble, without paying too much attention to the characteristics of the telescope itself. So here is a thorough comparison between the two space telescopes."
is the fact that while Hubble can view things in the optical, James Webb will be looking at things in the infra-red. The two Wiki links (from the article) provide much more information.
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/. is screwing up the text, but the links should still work.
http://en.wikipedia.org/wiki/James_Webb_Space_Tel
http://en.wikipedia.org/wiki/Hubble_Space_Telesco
Grr...
I worked on the Webb telescope project for a short period of time (back when it was Next Generation Space Telescope) and, believe me, they had a hard enough time scrounging up the money to create what they have now. Making the mirror "a little bigger" or increasing the size of the infrared array would require much more effort than you might think.
There is an optical limit or boundary which cannot be seen past - the surface of last scattering - preventing you from actually seeing right to the beginning.
Batman: "Slake your thirst. You'll have worse than a parched sensation when we're through with you!"
Running Webb at L2 will save money. It's difficult and expensive to run a large space telescope in low Earth orbit (LEO). Observations have to be planned carefully since the Earth gets in the way for most of the sky every 90 or minutes. The satellite also has to have batteries to power the systems when the satellite/telescope is eclipsed by the Earth. Batteries are heavy, have to be recharged and they fail. Hubble's are failing. Large satellites in LEO slowly see a degeneration of their orbits because of drag from the very highest parts of the Early atmosphere. This requires them to be reboosted very so often. Any future service mission to HST needs to also reboost it.
Finally, satellites in LEO - least ones in orbits like the one HST is in - have to travel through a radition belt every orbit that can cause electronics to fail and bits to flip. This sometimes causes the telescope to go into safe mode and ruins observations. While in safe mode, operations crews are standing around and more observations have to be either cancelled or rescheduled.
Many of these problems are avoided at L2 or similar locations. Webb's life will be limited by the amount of sensor coolant on board, but space telescopes like the International Ultraviolet Explorer have operated for 20 plus years. IUE used a small crew, was easy to operate and produced more then 3,000 papers at a very low cost - a great return in value for tax payer.
No, sorry. There is a limit to how far we'll ever to able to see, and it's called our "light cone".
John Barrow's book "Impossibility" has a nice description of this (and other limits).
The orbit is about 1.5 million km distance from the earth, at something called the L2 Lagrangian. The Webb wiki page has a link to the Lagrangian page, but for the lazy people, it's here. The orbit was chosen to keep the position of the sun constant relative to the telescope, so that the big 'parasol' can be used to shield the infra-red sensor.
As for Hubble, it's been able to give some awesome images, but it has its limits. I was hoping that the JW (henceforth called J-Dubya?!) would be able to start spotting planets around other stars, but it's not designed for that. I'd like to know if it's theorically possible to keep both in orbit and use them in parallel somehow, in the same way that ground-based radio telescopes have been linked together in arrays. Probably not worth the hassle?
The 'infra-red only' sensor troubles me. Since the telescope's aim is to study the Big Bang, the light/photons it'll be receiving will have travelled for a long time/distance and I guess be red-shifted way down to the IR band. This is all very well, but it means that the telescope shouldn't be considered as a replacement for Hubble, which carries out a wider range of observations.
As an aside, I believe that there is a limit to how far back we can look. At some point, probably less than 1 million years (a guess, can anyone help?), the universe was just too dense for photons to travel around unhindered as they seem to these days. Who said it was better back in the old days eh?
Now two questions. First why beryllium? I know that it's lightweight so easier to lift into orbit. Any other reasons? And secondly what happens if a micro-meteor hits this shield? Do we get a permanent bright spot on all subsequent images, like a broken pixel on an LCD display?
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