Iridium Communications Inc. owns a constellation of telecommunications satellites that are among the brightest and most observable earth-orbiting satellites. Each Iridium satellite is equipped with four main mission antennas (MMAs) that at certain angles can reflect a narrow track across the Earth's surface, which is visible to an observer as a flare that rapidly increases and then diminishes in brightness. This distinctive flare can be as bright as magnitude -9 and is sometimes visible in broad daylight.
Iridium flare data is obtained from heavens-above.com.