Find an Iridium Flare

An Iridium flare is a specific type of satellite flare (also known as satellite glint) made when the antennas of an Iridium communication satellite reflect sunlight directly onto the surface of the Earth. Whoever is looking at the right spot at the right time will see a brief but bright flare in the sky which is sometimes brighter than Venus and even the Moon (when it's not full). However, you don't have to depend on sheer luck to see an Iridium flare. With data giving the location of the satellites around the Earth, a program can easily calculate the time at which an observer will see the sun's reflection on the antennas.

Steps

  1. Determine your location in coordinates (latitude and longitude). You can use an online service.
  2. Use a prediction program and input your coordinates to determine the time and location of an Iridium flare in your area.
    • Heavens-above.com - online service that can predict Iridium flares as well as determine coordinates

      • Find your location using one of the options listed.
      • After submitting your coordinates, find a section that says, "Iridium Flares". Click on the "next 7 days" link, or the "next 24 hrs" link if you wish.
      • Find an Iridium flare listed (the time listed is 24-hour local time). Write down the date, time, altitude and azimuth.
    • SKYSAT -- 16-bit graphical satellite prediction program that also indicates possible flares from Iridium and other satellites
    • IRIDFLAR -- DOS based program
  3. Recheck the prediction shortly before observing. Flares that are forecast days or weeks in advance might not be accurate, so they might be brighter or dimmer than expected, come earlier or later, be in a slightly different point of sky, or sometimes not appear at all.
  4. Make sure your clock or watch is tuned as precisely as possible, otherwise you'll likely miss it or be too early and think it's over. Some TV channels, such as some weather and news channels will list the time to the second. There are also websites that list time accurately, some in UTC and others in local time. The Atomic Clock in Boulder shows all U.S. time zones or UTC.
  5. Go outside at least a couple of minutes prior to the time listed on the correct date. See if the sky is clear or at least partially clear, or else you will not be able to see the flare. This will allow you time to gauge the correct place in the sky to watch. Also, you can usually see the satellite as it approaches the 'flare' point, if you're on-site a little early.
  6. Look in the direction and altitude listed. An Iridium flare looks like a star that moves slowly and quickly brightens, then slowly fades away. If it looks elongated, leaves a visible trail, fades away in less than a second from becoming visible, or lasts more than a minute, it is most likely either a meteor, a fireball, or the ISS (International Space Station, which can also be found with similar methods).
    • Azimuth - Measured clockwise around the observer's horizon from north; north has an azimuth of 0°, east 90°, south 180° and west 270°.
    • Altitude - Overhead is 90°, directly in front of you is 0°. Determining the correct altitude to watch is a bit more difficult than the azimuth, especially in the twilight before stars begin to appear, which is the usual time satellites are seen. A handy gauge is your fist held at arm's length - it is approximately 10° 'tall'. I prefer to also extend my index (pointer) and pinky fingers straight out (not 'splayed') to provide a better 0° and 10° gauging point. Place your extended pinky on the horizon in front of you, look up to your index finger & note where it is against the sky -- count "10". Keep your eyes on that spot, and shift your fist upwards until the pinky is where the index was - then up to the index's new position & count "20", & so on. Repeat until you've determined the correct angle - and of course, a 5° (eg, 45° etc) position falls in the middle between the extended fingers. This 'gauge' is pretty accurate. You can continue up to 90° & if that point is directly overhead, you're doing it correctly.

Tips

  • You may want to bring a camera or pair of binoculars, or a telescope if you are going to attempt to photograph it. Don't expect to see the satellite itself in any detail, though -- you will only see the sunlight reflecting off it.
  • Some flares can occasionally appear in daytime and become bright enough to be visible.
  • You can also photograph or video an Iridium flare, but make sure it is pointed in exactly the right direction, zoomed in, and you are moving the camera at the right speed. You might also have to adjust the camera settings.
  • The further into the future the forecast is, the less accurate it will likely be.
  • "Iridium" is a brand name, chosen based on the number of satellites originally planned for construction. The satellites are not actually made of iridium.
  • Heavens-above.com treats anything lower than 10° altitude as invisible (trees, buildings, "atmospheric extinction" from haze etc). If you have a clear view of the horizon, sometimes you can see things before or after they are scheduled to appear or disappear.
  • If you are familiar with the sky, you may look at the star maps available to locate it. You might use this to try to photograph the satellite through a telescope, but remember this is very difficult. The ISS is actually easier to photograph.

Warnings

  • Occasionally the time listed on the predictions may be off, if it says Standard Time when the times listed are actually supposed to be during Daylight time or vice versa.
  • Do not stare at the sun for too long or you will cause irreversible damage to your optic nerves. While good advice any time, this should not be a factor as most satellites are only visible during twilight hours, when the Sun is below the horizon. For daytime flares, the satellite must be at a sufficient angle from the Sun's direction to lessen any danger of staring at it, else you couldn't see the flare.

Things You'll Need

  • Camera, pair of binoculars, or telescope (optional)

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Sources and Citations

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