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Frequently asked questions (FAQ)

The flare I went out to see didn't appear. What was the reason?

Sometimes, but not often, flares fail to appear completely. There are several possible reasons;

  • The satellite could have recently failed, and its attitude is no longer tightly controlled. Several Iridium satellites have failed since they were put into orbit and are no longer in either the nominal attitude or orbit. As soon as we know that a satellite has failed we remove it from our predictions, but one that has only recently failed may still be flagged as operational and erroneous predictions will be in our list.
  • The satellite could be temporarily in a non-nominal attitude. This can happen, especially shortly after launch, when a satellite is being checked out, or maneuvering. If it isn't in the expected attitude, the chances are the flare will not appear since the geometry between sun, satellite and observer is so critical to a flare appearing as predicted.
  • You could have been looking in the wrong direction! Please make sure you understand what the azimuth and elevation angles mean in the predictions table, and don't confuse the direction to the flare centre which is shown on the small map of the flare details page with the azimuth of the flare which is the direction you should be looking.
  • You could have been looking at the wrong time. An Iridium flare only lasts for a few seconds, and if your watch is not set accurately, or you look away even for a few seconds, you could miss it. You can use our "What time is it?" page to get an accurate time.
  • Your coordinates or time zone could be entered incorrectly. Please make sure that you have entered the correct coordinates for your location. Iridium flares are especially sensitive to position errors, and you should try to enter your coordinates to 1km (about 0.01°) accuracy if you can. Also check that your time zone is correct. You can do this by comparing the local time given on our "What time is it?" page with the current time at you location.