Re: Questions about future of space telescopy
From: Mike Dworetsky (platinum198_at_pants.btinternet.com)
Date: 11/23/04
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Date: Tue, 23 Nov 2004 10:24:34 +0000 (UTC)
<petro12@mail.com> wrote in message
news:4eccbeed.0411222222.66fdf3b@posting.google.com...
> I have a couple questions, they all related to the future of spece
> telescopes:
>
> 1. Hubble's Telescope has < 0.1 arcsec resolution in visible and
> ultraviolet ranges. What is the next resolution level that can bring
> substantially new knowledge about the Universe ? Of course the higher
> resolution the better, but what is a thershold to gain new knowledge ?
>
Many astronomers would settle for 0.1 arcsec with 100 times the light
gathering power...the great advances will come from being able to do
spectroscopy, not just from resolving things. Resolution will help in
specific problems, including the search for direct imaging of extrasolar
planets, and examining starbursts in the very early universe.
> 2. As far as I know there is deep interest in using far infrared to
> peek into the centre of our Galaxy. What is the current limiting
> factor here - resolution (mirror size), or a need to cool the
> telescope down ? In case of cooling - is it enough to shield the
> telescope in space to bring the temperature its elements close to 0K,
> or it has to be launched far off Earth orbit (far from the Sun), or
> some active cooling can be used ?
>
You always want the biggest mirror you can afford, mainly for
light-gathering power rather than resolution, though resolving power is
helpful.
All such IR telescopes have to be cooled, if possible by liquid helium. It
is not sufficient to shield such a telescope, active cooling is required.
The main reason for moving such a telescope away from Earth (say to L2) is
that Earth is a huge source of IR radiation, and this makes the coolant run
out much faster. The Sun is a problem, but not as big a problem as Earth,
because a reflecting shield that works against visible light is relatively
easy to make, but it is hard to build an efficient reflector of far IR
wavelengths.
In space, you can cool the optics as well as the detector; on Earth, this is
n't possible due to the atmosphere and ice condensation.
> 3. Telescopes interferometry can be used to achieve much higher
> "resolution", provided that the shape of the observation object is
> known. My queston is - what it can be used for, in addition to
> measuring stellar diameters, distances between double stars, etc ?
> What are the limitations there ?
>
The shape can become known through interferometry measurements, using
multielement interferometers like the VLT.
One of the big quests at the moment is the goal of imaging extrasolar
terrestrial planets directly. This can be achieved using "nulling"
interferometers. The TPF (terrestrial planet finder, or Darwin mission) is
such a space-based interferometer concept.
> I would also highly appreciate a pointer to good Web resources, or
> literature, on these topics.
-- Mike Dworetsky (Remove "pants" spamblock to send e-mail)
- Next message: Hannu K.J. Poropudas: "Re: APPROXIMATE ANCIENT TIME FORMULA BASED ON FOSSIL DATA (One Error Correction)"
- Previous message: Luigi Caselli: "Re: REDSHIFT IN A STABLE UNIVERSE"
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