Iridium satellites are satellites that are used for telephones and other purposes such as navigation. Most of them are in a controlled orbit, so the flares from these satellites can be predicted. Computer programs can be fed the satellite's information and can predict a flare to an observer's location. The iridium satellite is known for having a weird shape. It has three door-sized antennas that occasionally reflects sunlight back to Earth. These can be very bright. So much so, that it can even be seen during the day. This annoys astronomers because it disrupts their observations.