British Astronomical Association
Supporting amateur astronomers since 1890

Secondary menu

Main menu

Home Forums General Discussion
Terms of use

Bright point of light fading slowly in Pegasus

3 posts / 0 new
Last post
Offline
Last seen: 6 years 3 months ago
Joined: 10/01/2013 - 12:11
Bright point of light fading slowly in Pegasus

Posted by Mark Jones at 12:33 on 2013 Oct 08

Hi all. Last night my one year old decided to wake us up in the small hours and whilst a bottle of milk cooled I spent 5 minutes outside under a marvellously clear sky. I quickly noticed a bright 'star' in the wrong place, about 3 degrees north-east of Gamma Pegasi and as I watched over a few minutes it slowly faded and disappeared. The thing that struck me was that it clearly wasn't moving so was unlike any satellite or Iridium flare I've seen before. The time was about 04.15 BST. Does anybody have any idea what it might have been? I'm guessing a satellite but the lack of motion puzzles me. Unless it was moving away from me, perhaps. Regards,Mark

Offline
Last seen: 6 years 3 months ago
Joined: 10/01/2013 - 12:11
Re:Bright point of light fading slowly in Pegasus

Posted by William Stewart at 08:45 on 2013 Oct 09

Hi Mark,Not sure where you were observing from but I have assumed it was from somewhere near Manchester.I suspect you saw a flare (reflected sunlight) from a geosynchronous satellite.In the weeks either side of the equinox the sun, earth and satellites in geosynchronous orbits all lie roughly in the same plane and under such circumstances sunlight falling on solar panels and antennae on the satellites is reflected back in the direction of the earth at times close to "local midnight" for the satellite i.e. when it is on the opposite side of the earth from the sun. These reflections are most spectacular just before the satellite passes into the earth's shadow or just after they exit it. On earth they appear as a slowly brightening (and then fading) flare as the earth's rotation carries the observer through the projected spot of reflected sunlight. This would have been the case for a geosynchronous satellite in that part of the sky at around the time of your observation on the 08th October 2013.Being geosynchronous, it's orbital period matches the earth's rotation period and hence any motion across the sky would be difficult to see without optical aid. Your reported position is somewhat north of the main belt of geosynchronous satellites but there are a few that have non-zero orbital inclinations and hence oscillate north and south during each orbit.I've checked to see if I can identify the particular satellite but have so far drawn a blank - was it definitely to the NE (ie above and to the left) of Gamma Pegasi? I have a potential candidate (http://www.satflare.com/track.asp?q=90084#TOP) 5 degrees to the NW (ie above and to the right). For this particular satellite, it passed above the earth shadow and hence would have remained in sunlight.Geosynchronous satellites are typically about the size of a small bus (not counting the solar arrays) and are about 36000 km above the earth. They are visible to the unaided eye under the circumstances described above and hence are believed to the most distant man-made objects that can be seen without optical aid. Hope this helps.William

Offline
Last seen: 6 years 3 months ago
Joined: 10/01/2013 - 12:11
Re:Bright point of light fading slowly in Pegasus

Posted by Mark Jones at 13:50 on 2013 Oct 10

Hi William,Thank you for this excellent explanation. I've been studying the satflare website link and I am pretty sure this is what I saw. I'm actually near Leamington Spa but it doesn't make much difference. My estimate of the object's position was a little crude and looking at the positions on the sky map I think in my head I had put Pegasus the right-way up when saying 'north-east' (i.e. above and left). Looking again at the angle of Pegasus to the horizon at that time it was certainly more like 'north-west' and therefore the satellite you've identified seems to fit the bill. Interesting to see such a thing. It was something like magnitude -2 when I first spotted it, a little less than Jupiter perhaps. As I say it was immediately obvious as being a 'new star' in the wrong place.Thanks again,Mark