An "Iridium flare" is a bright light in the sky that appears for a few seconds (or more) and moves slowly for some distance.  (See Astronomy Picture of the Day for May 2, 2000.)  The brightest and most frequent Iridium flares are caused by intense reflections of the Sun from mirror-like "main mission antennas" on Iridium satellites. There are also predictable, though less reliable and not as bright, flares from the satellites' solar panels.

The brightest Iridium flares can be seen in broad daylight and thus are brighter than any natural object in the sky besides the Sun, the Moon, extremely bright fireball meteors, which are rare.

To see an Iridium flare, it is necessary to be looking at the correct position in the sky at the correct time!  Much more than with other satellites, with Iridium flares, in order to get the best results, personalized predictions for an exact location are best.

Iridium flares in general are so predictable that now they have been observed from the International Space Station, with it and the Iridium each moving, in different directions, at more than 17,000 miles per hour! Here's the story:
 
http://science.nasa.gov/ppod/y2003/28mar_iridiumflash.htm
 
More background on this is available in the following two messages:
 
http://www.satobs.org/seesat/Mar-2003/0186.html
http://www.satobs.org/seesat/Mar-2003/0196.html

Predictions for Iridium flares for a specific central Austin location — near West 35th Street and Shoal Creek (30.30 north, 97.75 west) — are given in the table below.  The times are in a 24-hour clock ("military time" format, where 18:00 is 6:00 p.m. and 21:00 is 9:00 p.m., etc.).

Along with each time, the sky positions are also given in the table, as "Azm" and "Al" angles.  "Azm" is a compass angle that tells whether to look north, south, east, or west, or in some intermediate direction.  "Al" is an elevation angle that tells how high to look above the horizon.

For the "generic" predictions below, the farther that the observer is from the "Flare Center", the less accurate the predictions will be. Being just a mile or two east or west of the flare center can make a very big difference in how bright the flare will actually be!

Note:  Due to variability in the attitude/orientation of the satellites —

The location and magnitude of Iridium flares are not perfectly predictable!

Note:  In order to see an Iridium flare – or anything else in the sky – it is essential to have an unobstructed view of the part of the sky where the Iridium flare (or any sky object) is to appear!

Note: Flares that are very low in the sky REQUIRE an UNOBSTRUCTED view in the direction of the flare. Also, if the sky is not perfectly clear, chances of seeing a predicted flare are reduced.

Note: Regarding predictions for satellites marked with "?" — these may still be somewhat less reliable due to some long-standing uncertainty in their status as spares in special orbits.

Note on daylight flares: It is REQUIRED that the observer be as near to the "Center Max Flare" as possible in order to have the best chance to see a daylight flare! This includes when the Sun is right at the horizon. Attempts to observe them from more than about 1/2 mile east or west of that location are much less likely to be successful.

The location used for these predictions is at latitude 30.30 north, longitude 97.75 west, which is near West 35th Street and Shoal Creek, close to the geographic center of Austin. [See map — about 30K.] 

An excellent Web site that provides Iridium flare predictions for any location is called "Heavens-Above", which is hosted by the German Space Operations Centre. To obtain personalized predictions from "Heavens-Above":

1. Get the latitude and longitude of the observing location using the street address (USA only; "address info.").
2. Get the "Heavens-Above" predictions. (Input the latitude, longitude, and time zone of the observing location and then follow links to Iridium flare predictions.)