Re: brightness of James Webb Space Telescope

From: Thierry Legault via Seesat-l <>
Date: Tue, 21 Dec 2021 08:11:34 +0100
Thank you Tony, this is interesting.

How can we take into account the fact that the sunshield is made of 
several layers of highly reflective aluminum coated Kapton and 
reflects lights (more or less?) towards the Sun, therefore towards 
the Earth considering the position of the satellite at L2?

I guess that if it were white (like the ISS radiators) it would be 
easier to assess its brightness from surface considerations, in this 
case it seems to me that the situation is closer to Lightsail, more 
unpredictable and highly dependent on the flatness of the shield and 
its precise orientation. Could we expect flares sometimes, visible 
through a telescope?
Does it make sense to extrapolate from Lightsail characteristics 
(distance and reflective surface)?


At 12:21 PM 30/10/2010, Tony Beresford wrote:
 >given the size (300 sq.m) and the average distance of an orbit around
 >the L2 Earth Sun point i would say mag 16.5
 >there are currently 2 European spacecraft at L2, Herschel &  Planck
 >There was until recently the US WMAP as well  but its mission has
 >All of these objects have been observed by a various
 >observing station who report minor planet positions to
 >the IAU's Minor planet Centre. They are a nuisance as far as the
 >asteroid astronomists
 >are and the MPC are concerned of course. The standard reporting 
form for these
 >objects as privately published by MPC staff has a crude magnitude 
estimate in a
 >variety of pass-bands. An typical magnitude for the Herschel telescope
 >is magnitude 20. its somewhat brighter for ESA,s Planck spacecraft
 >being magnitude 17.5 to 18. herschel is an IR telescope of 3.5m aperture,
 >while planck is looking at the cosmic background with a slightly
 >smaller aperture.
 >The Minor Planet Centre has a page with a menu offering predictions
 >for the objects mentioned and some others, accesable via the menu
 >selection of 'distant Artificial satellites' on the left hand
 >side of the page at 
 >further links on that page get you too a list of observations.
 >One is banned from jumping to the page I tried a some 12 hours
 >ago.  I guess this is simply a security measure.
 >Tony Beresford

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