Astronomy Down Under

NAGging

5 Oct at 12:56 by Wilson

Last night was this month’s meeting of the NAG, about which I wrote here. Differently from the other months, this meeting did not have a theme; it was the “nothing in particular” meeting.

Because of that, we spent most of the time outside, enjoying one of the few clear nights of the last few weeks. Unfortunately, the almost-full moon made sure that the only “interesting” thing to look at was, well, the moon (note to self: looking at the full moon with binoculars after allowing your eyes to adapt to the dark will ruin your night vision for several minutes).

There were a few small telescopes around, plus the ASV’s large 20-inch; plus, several people (myself included) had their binoculars at hand. The only visible planet was Jupiter, but it was very low in the sky and it dropped off behind the trees before the 20-inch was set-up (and cooled down). Uranus and Neptune were up as well, but in the same general direction of the moon and, therefore, not visible.

One highlight of the night was seeing the ISS; it showed up low in the southwestern sky and disappeared when it was starting to set in the northeast, after flying almost directly above us and staying clearly visible (as a bright orange dot) for over two minutes. This was quickly followed by a 0-magnitude Iridium flare, followed soon after by a spectacular -3-magnitude one, with an unknown satellite doing approximately the same path of the ISS minutes later. It’s definitely getting crowded up there. (heavens-above.com will tell you when the ISS and Iridium flares are visible from your location, and how to find them)

What are Iridium flares?

Satellite flares, in general, are bright flashes of light visible from the ground when the Sun light reflects off satellites flying above. The Iridium phone satellites, in particular, generate very bright flares due to their format; the flashes can go up to magnitude -8, and can be visible in bright daylight if you know where to look at. Flares are very localised events; the “spot” of light created on the ground is some 10km wide, so you need to know your location (latitude/longitude) failry precisely in order to find out about them. Google Maps can help with that.