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¡Sky
Watch!
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by
Jim Walker
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Iridium Flares are a new man-made astronomical phenomenon, very
bright points of light lasting about 10 seconds. These flares can
be as bright as -8 magnitude, far brighter than Venus - indeed, brighter
than anything else in the sky besides the sun and the moon. The flares
originate from sunlight reflected by the large solar panels on more than
70 Iridium satellites in low earth orbit. These satellites are part
of the Iridium system of global wireless phones and pagers.
Parks Goodwin saw a very bright, brief, light one morning by accident a
couple of months ago. I thought at the time he might have seen a point
meteor, a bright meteor headed directly toward the observer. Such
meteors have been observed, but very rarely. It now appears likely
that Parks saw an Iridium flare.
Barbara and I observed an Iridium flare at 06:09:17 AM on April 19 (note
the timing, predicted and observed to the second). The flare lasted
about 10 seconds and reached -5 mag, brighter than Venus, now about -4.0
(remember, larger negative mags are brighter, larger positive mags are
dimmer).
To look for a flare, you need to set your watch or clock as accurately
as possible. Several free programs can be downloaded from the web
site below. If you're not on the net and want to look for a flare,
maybe you can ask someone to help you synchronize your clock. (I
would be glad to help, but I'll be away for a few days at the IDA meeting
in Tucson.)
http://thefreesite.com/timerutils.htm
The web site below, that we printed last month courtesy of Shannon Rudine,
has information on Iridium flares as well as Mir, the new International
Space Station still under construction, and other satellites visible to
the naked eye.
http://www.gsoc.dlr.de/satvis/
The site lists more than 1,000,000 locations around the world. The following
times and positions of Iridium flares are from the above site.
For the sightings on the evenings of the 25th and 26th, if you look at
Polaris the flare will be in your field of view (see the star charts).
The indicated azimuth (compass direction) is 7 deg west of north, and the
elevation of 23 deg is almost as high as Polaris.
On the morning of the 26, if you look straight south (which is 180 deg)
and look up 2/3 of the way to the zenith, then the flare will be in your
field of view. The magnitude of -7 will be quite eye catching.
Some Bright Iridium Flares
|
Date
|
Local Time
|
Mag
|
Elevation
|
Azimuth
|
|
25 Apr
|
21:38:56
|
-4
|
23
|
353 (N)
|
|
26 Apr
|
07:03:38
|
-2
|
65
|
184 (S)
|
|
26 Apr
|
21:32:38
|
-7
|
25
|
353 (N)
|
Technological
marvels though they are, I can imagine situations where an Iridium flare
could be an annoyance, for example, in the middle of an astrophoto.
I also think we, as astronomers, can expect a lot of questions from people
who happen to observe a flare by chance. UFOs, anyone?
You can print a copy of this star
chart so you can take it outside.
