An Iridium Flare is caused by the Iridium constellation with 66 active telecommunication satellites in low Earth orbit are known to cause the brightest flares of all orbiting satellites. View A Magnificent Iridium Flare.
Satellite flare, also known as satellite glint, is the visible phenomenon caused by the reflective surfaces of passing satellites, reflecting sunlight toward the Earth below and appearing as a brief, bright “iridium flare”.
Time and place of the satellite’s flare can be predicted only when the satellite is controlled, and its orientation in space is known. In this case it is possible to predict the exact time of the iridium flare, its place in the sky, the brightness and duration of the Iridium Flare.
On this page you can track in real time all the satellites orbiting the Earth, with a 2D representation, predict their passes, view their trajectory, predict satellite flares and transits, find out the best location to see these events on a detailed Google map. Iridium Flare, you will know an Iridium Flare when you see an Iridium Flare.
Of the roughly 3,000 spacecraft in Earth orbit, nearly 100 stand apart: the Iridium communications spacecraft, which skim the uppermost, most rarefied region of the atmosphere (the exosphere) at altitudes around 800 kilometers in six steeply inclined orbital planes (orbits that nearly pass overhead at the North and South Poles). Known as an iridium flare, the glare from these satellites is well known to many astronomers.
Most Iridium satellites are still controlled, so their flares can be predicted. The Iridium communication satellites have a peculiar shape with three polished door-sized antennas, 120° apart and at 40° angles with the main bus. The forward antenna faces the direction the satellite is travelling. Occasionally, an antenna reflects sunlight directly down at Earth, creating a predictable and quickly moving illuminated spot on the surface below of about 10 km (6.2 mi) diameter. To an observer this looks like a bright flash, or flare in the sky, with a duration of a few seconds.
Ranging up to −8 magnitude (rarely to a brilliant −9.5), some of the flares are so bright that they can be seen in the daytime; but they are most impressive at night. This flashing has caused some annoyance to astronomers, as the flares occasionally disturb observations.
As the Iridium constellation consists of 66 working satellites, Iridium flares are visible quite often (2–4 times per night). Flares of brightness −5 magnitude occur 3–4 times per week; −8 magnitude may be visible 3–5 times per month for stationary observers. With the addition of the Iridium NEXT satellite constellation there will be several more Iridium flares happening on a daily basis.
Flares may also occur from solar panels, but they are not as bright (up to −3.5 magnitude). Such flares last about twice as long as those from the main mission antennas (MMA), because the so-called “mirror angle” for the solar panels is twice that for the MMAs. There are also rare cases of flares from MMAs and solar panels, or two MMAs (front and either right or left) of one satellite in a single pass.
The flares can be bright enough to be seen at night in big cities where light pollution usually prevents most stellar observation. When not flaring, the satellites are often visible crossing the night sky at a typical magnitude of 6, similar to a dim star.
In financial circles, the Iridium “constellation” of satellites stands apart because it was built at a cost of roughly $5 billion, only to be sold for $25 million when its first corporate owner, Iridium LLC, went bankrupt in 1999. The spacecraft (and the ground stations supporting them) were intended to enable owners of special portable telephones to communicate from any point on the surface of the globe. However, Iridium LLC never obtained the millions of customers needed to make the project profitable. The U.S. Department of Defense and Federal Emergency Management Agency are among the principal customers of the satellites’ current corporate owner, Iridium Satellite LLC our of Leesburg, Virginia.
In skywatching circles, the Iridium satellites stand apart because their flat, shiny, door-size antenna arrays (three per spacecraft) periodically reflect sunlight toward the ground, causing brief (seconds-long) but brilliant iridium flare that can momentarily reach an apparent magnitude of –8 — outshining the planet Venus. What’s more, these iridium flares are predictable, thanks to the satellites’ publicly available orbital elements and to software and Web sites that satellite-watching aficionados have made available free of charge.
There are many controlled satellites in addition to Iridium satellites, which can also flare, but most flares of these satellites do not exceed magnitude −2, therefore, they are often overlooked. Unlike and Iridium Flare.
MetOp-A and B, however, can produce predictable flares up to −5 mag. Four COSMO-SkyMed satellites can produce flares up to −4 mag., but their peculiarity is that they last much longer than the Iridium flares.
Most flares from other satellites are almost indistinguishable from a dim Iridium flare.
For a satellite can be observed directly, it is necessary that the sunshine reaches its structure and is reflected into our eyes. For that to take place, it is necessary that the following factors are present at the same time:
As a general rule, the closer the satellite passes over our station, the better the observation will be. That closer approach is directly related to the height of the satellite above the horizon line. The angle formed between the satellite and this line is called the elevation angle and the bigger this angle is, the closer to us the satellite will be.
The apex of that approach takes place when the satellite is exactly over the zenith, in other words, 90 degrees above the horizon, but not all the passages effectively reach that position.