Sunday, October 13, 2013

Iridium flares over Paris

Last night I saw my first Iridium flare.

What's an Iridium flare, you say? Well, see, there's this satellite telephone company that sells telephone services all around the world, called Iridium. The telephones they use relay calls via satellite … which means that the telephones can be used anywhere on the planet, even in the middle of the Pacific Ocean or at the South Pole. The system depends on dozens of Iridium satellites, which whirl around the Earth in orbits about 400 miles above the planet. Now, these satellites have a couple of large, flat, shiny antennas on them, and when they are in certain positions, sunlight can reflect off the antennas and down towards Earth. And if you happen to be in the right spot at the right time, you'll see the sunlight glinting off the satellites' antennas. This produces a very bright light in the sky (bright enough to see in daylight, sometimes) that fades up and then fades out over the course of a few seconds. This glint of sunlight visible from Earth is called an Iridium flare. Other satellites produce flares by reflecting sunlight, too, but the Iridium flares are easiest to see because of their door-sized, flat antennas.

Anyway … I had to go to the laundromat, which isn't very far away. I have a washing machine, but my neighbor complains that water leaks from her wall if I use it, even though there's no leak on my side, so I use a laundromat (see my previous post on all the water problems in the building). I've been putting off this visit for a long time. But I had virtually nothing clean left, so I put all the dirty stuff in plastic bags and took it to the laundromat.

It takes about 90 minutes to wash and dry the clothes. During that time, there's not much to do. I bought a big towel for the floor of the apartment in anticipation of the mess that the plumbers will make tomorrow. Then I sat on a bench on the nice pedestrian median near the Montparnasse Tower to wait for the clothing to wash.

I had my handy iPhone, and it's chock full of cool apps (cool to me, at least). I decided to check the sky with my beloved astronomy app, Sky Safari. I had used it once before, a few days earlier, to kill time while waiting 2.5 hours for locksmiths to arrive to open my stuck door (see again my previous post). On that occasion, I had been delighted to correctly identify Vega and Altair, two of the handful of stars that are visible in the sky even in well-lit Paris. Last night I was able to do the same, only it was easier because the sky was very clear (although streetlights still got in the way).

After identifying a few stars, it occurred to me to fire up my Iridium-flare app, which gives me the details on all visible Iridium flares in my area, using information published by the excellent Heavens Above Web site. I was pleasantly surprised to see that a very bright flare of satellite Iridium 31 was due in just ten minutes! So I tracked the satellite with Sky Safari, which was just coming up over the horizon in the north, and scoped out the exact location, near the Moon, where the flare would appear.

It so happened that a friend of mine walked by just as I was doing this, and said hello. But I was so engrossed in looking for the right spot in the sky and so afraid of missing the flare, that I just kind of sort of waved in her direction and asked her to wait for 30 seconds or so. I'm sure she thought I had lost it, since I was looking at the sky in all directions and saying things like "any second now" as if I expected our new insect overlords to descend in spaceships and take us (or me) away. She was kind enough to indulge me, however, and waited as I searched around.

At exactly 18:30:47, Universal Coordinated Time, Iridium 31 flared in the night sky, just east of the Moon. Suddenly a point of light appeared in the sky and brightened until it was as bright as the Moon, then faded back into darkness. I pointed to it and yelled "there it is!" and fortunately my friend and her company saw it when I did, proving that I was not psychotic. I explained to my friend et al. what the flares were all about, as she nodded indulgently. But they saw it, too, so they knew it wasn't a hallucination on my part. Of course, experienced skywatchers and amateur astronomers know all about Iridium flares, and spotting them is a popular pastime.

It was pretty cool. It was interesting to be able to see something without a telescope and without binoculars, and even against the relatively light-polluted sky of a big city. The flare was very obvious and easy to see. I'll have to keep an eye out for more in the future.

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