Re: brightness of James Webb Space Telescope

From: Marshall Eubanks via Seesat-l <seesat-l_at_satobs.org>
Date: Sat, 25 Dec 2021 10:27:00 -0500
On 2021-12-23 15:13, Daryl Bahls via Seesat-l wrote:
> On a slightly different, but related topic.  What would the expected
> brightness be shortly after launch at a range of 100,000 to 150,000 km?
> 
> I have a friend who is going to attempt (weather permitting) to 
> photograph
> JWST during that first night pass over the western hemisphere and we 
> were
> wondering what we may, or may not see.

Amateur astronomer "Sajith" reports on the comet-ml that he saw it in 
India shortly after launch as a "comet-like object"

 From this image of its underside, I think that this is going to be a 
pretty bright object out at ELS-2 once it's fully deployed.

https://twitter.com/TM_Eubanks/status/1474750295238496259/photo/1

The solar panel deployment has been confirmed, the Webb is power 
positive, and so it's even larger now.

https://twitter.com/astrofaisst/status/1474724558938640385/photo/4

Note that these images were taken from the ESC-A upper stage, which will 
also go out towards the Lagrange point (even if it doesn't stay there). 
The ESC-A is 5.4 meters diameter; oddly, I can't find a length for it, 
but it looks to be about 10 meters long. It should also be pretty 
visible for the next few days.

https://www.esa.int/Enabling_Support/Space_Transportation/Launch_vehicles/Ariane_5_ECA2

Regards
Marshall

> 
> Daryl
> 
> On Mon, Dec 20, 2021 at 11:12 PM Thierry Legault via Seesat-l <
> seesat-l_at_satobs.org> wrote:
> 
>> 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?
>> 
>> https://en.wikipedia.org/wiki/James_Webb_Space_Telescope#/media/File:James_Webb_Space_Telescope_2009_bottom.jpg
>> 
>> 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)?
>> 
>> Regards
>> 
>> 
>> 
>> 
>> 
>> 
>> 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
>>  >finished.
>>  >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
>> <http://www.minorplanetary.org/>http://www.minorplanetary.org
>>  >further links on that page get you too a list of observations.
>>  >One is banned from jumping to the page directly.as I tried a some 12
>> hours
>>  >ago.  I guess this is simply a security measure.
>>  >
>>  >Tony Beresford
>> 
>> 
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Received on Sat Dec 25 2021 - 09:29:21 UTC

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