What was that?
 

Last night I was watching the ISS pass over (I'm in Cambridge, UK). I looked down for a moment - when I looked up again there was what *looked* like another satellite going slightly North of East. I checked the time - 21:36BST. Looked up heavens-above to see which other satellites might be visible at that time - none that matched the track or time or brightness level. Looked up FR24 to find no aircraft overhead either. (Also no noise). In any case its apparent velocity was maybe three times as much as the ISS implying something moving fast at a suborbital level; my tentative conclusion is a weather balloon. But - would it catch the sun? I've found (web search) that sunset is a minute later for every 1.5km of altitude. As yesterday's sunset was 20:57, that gives an altitude of 60km - weather balloons tend to the 18-37km range and the record is 53km.

Any suggestions?n (Apart from "get a life", that is).

Lasted too long to be a meteor. I found a tracking site which confirms it.

Second stage of the Atlas V/Starliner perhaps.

Identified Flying Object
 

That would make sense, thanks. Roughly 24 hours after launch it's still somewhere near the 98nm initial trajectory, so not yet burning up, but is high enough to catch the sun, and crosses the sky about four times faster than the ISS. That assumes that the initial trajectory is more or less orbital - which would make sense, you want something fairly stable in case of delays, rather than find yourself plummeting earthwards only a few minutes after planned separation. In addition the path was in the same general direction as the ISS (maybe 15 degrees out?). And of course it would be following up behind - I believe SOP from year dot of orbital rendezvous has been to do that.

I guess heavens-above don't bother with ephemeral and less-predictable events.

A genuine thank you.