On 15/07/2011 12:29 PM, Quadibloc wrote:
One thing about the JWST that disturbed me was the fact that its
mirrors are coated with gold.

While at the present time, the infrared is a very exciting area for
astronomy, the fact that gold is strongly colored instead of
reflecting all colors equally seemed to me to be precluding the use of
the telescope for astronomy at other wavelengths.

If it was to be used in other wavelengths, then they would've put
cameras sensitive to other wavelengths onboard. They have only put
infrared cameras onboard, and once it's launched they won't be able to
put any other kind of camera on it.

Of course, it isn't just the primary mirror in the JWST that is coated
with gold. Also, since the JWST has a segmented mirror, another issue
arises - on Earth, observatories can use adaptive optics to compensate
for Earth's atmosphere, but with current technology, this works much
better in the infrared than in visible light.

The reason for having adaptive optics on ground telescopes is to deal
with atmospheric blurring. In space, they won't have any of those
problems, obviously.

But since a gold-coated primary, _in itself_, doesn't preclude using
the JWST to obtain images in blue, green, and ultraviolet light - the
brightness of which can be adjusted to compensate for the lower
reflectivity of gold at those wavelengths - if it *can* be designed to
avoid being limited to working at wavelengths longer than a limit such
as 720 nm or 560 nm, I would think it is worth the effort.

Don't worry, they'll make the images available for you to see in
wavelengths you recognize.

Yousuf Khan