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Posted by Steve Holmes2 at 13:48 on 2013 Jun 13
I was preparing to observe (by eye) a pass of the ATV-4 on the night of Tuesday 11th June. Arcturus, near to which the ATV was to pass, was very bright in the south so I was keeping an eye on that general area in case I missed the ATV on the rising part of its pass. Suddenly, "another Arcturus" appeared slightly above it and somewhat to its left and began to move slowly from left to right. I was sure this could not have been the ATV so I moved my gaze to where it should then be, and picked it up immediately. I then looked back towards Arcturus, to find that the mystery object was no longer visible.I was absolutely convinced that the object was not an aircraft or a helicopter (both of which are frequently seen in our area) nor something like a "hot-air lantern" so I consulted the Heavens-Above website to find that the Terra earth-observation satellite was passing at the exact time (22:56 BST) and place when I had seen the mystery object (as had my wife, so I wasn’t imagining it!). Its quoted magnitude was only 2.0 though, so it would not have been easily visible, and definitely not as bright as Arcturus (mag 0.0). I thus presumed I had seen a "flare" from the large solar array panel carried by Terra (in the same way flares are produced by the Iridium satellites).This is all rather conjectural though, so I wondered whether anyone else happened to have also seen this event? The geographical area where a flare is visible is rather restricted so it would probably need to be another observer in north Suffolk (I’m at 52.30deg N, 1.37deg E).Any observations or comments?Steve Holmes
Posted by Peter Meadows at 21:43 on 2013 Jun 13
Steve,Here is an image of another Earth Observation satellite, Envisat, which shows flaring. The image was taken last August (5th at 21:16 UT). The Summer Triangle comprising Deneb (top left of image), Vega (middle) and Altair (bottom left) and some high thin cloud are also shown. Peter
Posted by Steve Holmes2 at 01:09 on 2013 Jun 14
This image has a number of interesting aspects:-1) The track of Envisat across the sky as shown by the stars you mention is pretty-well parallel to that of Terra as shown on Heavens-Above. This confirms that the actual orbit of Envisat is polar, as for Terra, which is quite usual for an earth-observation satellite.2) The brighness profile of the flare is totally different from that of an Iridium flare or of the one I saw. This one seems rather more of a "flash" than a flare: Iridium flares tend to build up and die down fairly steadily over a period of about 30sec. The occasional one has a very bright central portion (when you’re close to the "centre line") but still has the steady build up and down. The Envisat "base level" is much less bright than for an Iridium flare.3) The Envisat image shows a number of subsidiary flares to the lower left of the main "flash". These are presumably caused by different parts of the satellite catching the sun before the main solar array, which doesn’t happen with Iridium flares.For comparison, here’s a couple of shots of Iridium flares. The first one has an unusually bright centre section (actually mag -8 or brighter!) and the second is a quite rare double flare – it’s a single exposure of 30secs, capturing two adjacent flares just 6 sec apart.
Bizarrely, while I was composing this reply I popped outside to see whether the sky was clearing and, purely by chance, saw a flare low down in the west! This was not listed as an Iridium flare by Heavens-Above but IGS 1A was passing that exact spot at the right time so I assume that’s what it was. The IGS family is known to flare, which raises the possibility that the "event" I saw on 11th June was caused by IGS 5A rather than Terra: it had almost exactly the same track but was close to Arcturus 1min earlier (which is within the tolerance of my "quick look at my watch in the dark" timings).Further comments invited.Steve Holmes
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