Up in the Sky - It's a Bird, It's a Plane, It's...

An Iridium Flare!  Tonight we had an excellent appearance that was magnitude -7, which makes it about as bright as the quarter moon!  This one appeared in our southern sky - the bright star near the bottom is Fomalhaut, the brightest star in Piscis Austrinus (Southern Fish).  It is a 30 second exposure with a 50mm lens at F/4.5.   I've mentioned the flares before, but perhaps never fully explained them, so it is about time to remedy that.

The Iridium satellite constellation is a set of 66 satellites that provide world-wide handheld phone communications.  Originally there were to be 77, matching the atomic number of the element iridium, thus the name.  A peculiarity of the satellite is that there are 3 flat polished antennae, and with it's orientation fixed in space, these antennae can predictably reflect sunlight down onto the night-side of the earth.  These flares can be as bright as magnitude -9, possible to see even in daytime, and can be spectacular at night.  The flatness accuracy of the panels is such that the projected sunbeam is only a few miles in diameter.  In addition, there are websites, such as Heavens-Above, that will predict when these flares will pass over your position on the earth.  It can be quite amazing watching even from urban areas a dim satellite appearing and growing brighter by thousands of times to brilliance, then fading slowly again to invisibility, all in a few seconds.  The flares are quite popular at the Grand Canyon Star Party, where the public treats us as shamans for our ability to predict their passing.

The Royal Astronomical Society of Canada has a nice website explaining the geometry and effects of the flares, including detailed instructions to logging into heavens-Above to be able to predict these far in advance, including appearances of the International Space Station and, in fact, any satellite currently in orbit!  They are the source of the illustration at left showing the effect of the antenna reflection.

Observing the flares is a lot of fun, and so easy to do with the assistance of Heavens-Above.  In addition to predicting Iridiums and the ISS, they can plot out the path of the satellite as it goes across the constellations.  They also plot out the positions of any bright comets or asteroids that are visible, and you can plot out a whole-sky map for any time or date you desire.  With those tools and a few satellite observations under your belt, you are on your way to learning your way around the sky.