IridiumFlares

Some unintended side-effects are wonderful. The Iridium satellite phone system cost billions of dollars to put into orbit and has already gone through bankruptcy to new ownership. Calls using this technology are frightfully expensive and have to be made outdoors using heavy handsets. It's unclear whether Iridium will ever be economically viable. Space is a harsh environment, especially for making money.

But aside from their orthodox functionality, the Iridium spacecraft play a neat trick: they flare. Each orbiter has three shiny, flat antennas on its sides, as big as a the front door of a house. What you've got, therefore, are some lovely mirrors that glide along ~500 miles above the Earth. Sunlight hitting an antenna bounces off it. When conditions are just right a satellite is exposed to daylight, it's after sunset below, and the reflected beam shines down with a dazzling brilliance. Given the dimensions of the mirrors and the angular size of the Sun in the sky, the area that a flare covers is a few tens of miles across. That illuminated spot zips along the surface of the Earth at the speed of the spacecraft, roughly five miles per second.

An Iridium glint is hundreds of times brighter than the brightest stars or planets. In astronomical language, flares can be as much as -7 or -8 magnitude, comparable to a half-moon. (see LogScales, 23 Feb 2000, for more details of how stellar magnitudes work) The phenomenon is dramatic: starting from invisibility, a spark begins to glow high in the night sky. It creeps along, growing stronger and stronger, until in a few seconds it gleams like a powerful airplane landing light ... and then it fades again, and vanishes.

In 1997 Iridium flares were discovered, by amateur space enthusiasts. There are several score satellites, enough to give a number of nice flares every week at any given point on the ground. Some have even been seen in the daytime, by those who know just where to look. Because the spacecrafts' locations and orientations are well-defined, flares are quite predictable --- given enough orbital mechanics and cleverness with equations. One handy online service, http://www.heavens-above.com in Munich Germany, will compute forecasts a week ahead for any latitude and longitude.

A friend told me about Iridium glints in 1998, and for a spell I was seriously enraptured by them. I would print out tables of locally-visible flares, synchronize my watch with the Naval Observatory, and set an alarm. Then when the time came I rushed out into the front yard to look. I knocked on my neighbors' doors and dragged them out too. Even while driving my kids to their music lessons, if a flare was scheduled I pulled over to the side of the road, jumped from the car, and stared up at the sky. Whenever I go past a place where I saw a good Iridium flare that way, I still remember it ... in front of a mini-mansion on Old Military Road in northern Virginia ... at a corner on New Hampshire Avenue in Takoma Park Maryland ... in the parking lot of Walt Whitman High School in Bethesda ....

Yep, I had a bad flare jones. But I'm better now. Really.

(for more information, see http://www.satobs.org/iridium.html or http://users.skynet.be/sky56407/htmleng/iridium.htm etc.; in the ZhurnalWiki see also GeoMemory (17 May 2001) re spatially-linked recollections, and HighGlider (8 Oct 2000) for an effort to versify about this sort of thing)


TopicScience - TopicPersonalHistory - Datetag20011230



(correlates: Ninjas vs. Pirates, IncomprehensiblePhenomena, GlassDarkly, ...)