Atlantis Touches Down. How To See Spectacular Iridium Satellite Flares

Space shuttle Atlantis lands for the final time at NASA’s Kennedy Space Center in Florida earlier this morning. Image credit: NASA/Bill Ingalls

The space shuttle Atlantis landed at 4:57 a.m. CDT today at Kennedy Space Center in Florida after 200 orbits around Earth and a journey of 5,284,862 miles. Now that it’s back home, Atlantis won’t be going far. It’s slated to spend its retirement years on display at Kennedy’s Visitor Complex.

The shuttle crew delivered more than 9,400 pounds of spare parts, spare equipment and other supplies in the Raffaello multi-purpose logistics module – including 2,677 pounds of food – that will sustain space station operations for the next year. As part of space station ‘closet cleaning’, Raffaello brought back nearly 5,700 pounds of unneeded materials. Staring this weekend, the International Space Station, home at the moment to six astronauts, will begin making passes across the dawn sky for much of the U.S. In Sunday’s blog, I’ll post a table of times when to watch for it.

The Iridium 96 satellite looks like a fireball as it briefly flares while passing over the neighborhood in July 2008. Photo: Bob King

The return of the space station got me thinking about Iridium satellites and the spectacular flares they produce when sunlight hits them just so. I’ve written about Iridium flares in the past, but now is a good time to revisit the topic. Summer weather brings more of us outside under the night sky, increasing the chance we’ll see one of one of these jaw-dropping events.

There are some 66 active Iridium satellites orbiting the Earth like electrons around the nucleus of an atom. They form a global ‘constellation’ 485 miles high used for relaying voice and data communications. The name ‘Iridium’ comes from the element iridium which is number 77 on the periodic table. The constellation was originally to consist of 77 satellites, but more have been launched over the years.

A mirror-like reflection of a bright light source off one of the antenna arrays on an Iridium satellite. Credit: SeeSat-L

Normally Iridiums are too faint to see except in binoculars, but they have silver-coated Teflon antenna arrays that reflect sunlight like a mirror. When the angle between satellite and observer is right, a brilliant reflection of the sun from the antennas causes an Iridium to suddenly and spectacularly brighten for between 5 and 20 seconds. Unlike a meteor, the satellite does not dash across the sky as it flares. It moves very slowly due to its high altitude, more than twice that of the space station.

Flares range in brightness from that of the Sirius, the brightest star in the sky at magnitude -1.4, all the way up to about -8, which is 20 times brighter than Venus (-4.5)! I’ve seen a few -8 flares, and they’re so intense, you think the object’s going to explode. Almost as suddenly as it appeared, the satellite fades back to invisibility 15 seconds later. Crazy.

There is one caveat, well, two really. Make sure your watch or cellphone is set to the correct time so you don’t miss the brief event. Secondly, flares are only visible with a range of less than 50 miles. The flares I see at my house will be brighter or fainter than the same seen across town.  That means you’ll need to find when they’re visible for exactly where you live.

The best and easiest to use resource is the Heavens Above website. Once there, login and select your location. Under the Satellites heading on the left side of the page, look for Iridium flares and click on the Next 7 days link. You’ll be taken to a page that shows a table of dates, times, intensities (the higher the negative number, the brighter the flare), the satellite’s number and its altitude and azimuth. Altitude tells you how high to look. If it’s 90 degrees, that’s overhead. If 45 degrees, that’s halfway between the horizon (0 degrees) and overhead.

This time exposure shows the how a flare from Iridium 75 evolved from invisibility (right) through peak brightness and then fadeout. Photo: Bob King

Azimuth tells you what direction to look. Due north is 0 degrees azimuth, east is 90, south is 180 and west 270. The final bit of information is how far you are from the flare’s center, where it reaches peak brightness. Click on the time link to see where the center is. For example, tonight there’s a nice -3 magnitude flare for my location at 9:44 p.m., but I see from the table that I’m 17.7 km west of the flare’s center. If I drove 17.7 km to the east, I’d see a humongous -8 magnitude flare instead. Will I do this? Only if I were able to drive my car on Lake Superior.

Heavens-Above even has a listing of flares visible in broad daylight. Too cool. However you see Iridium flares, bring a friend along and surprise them by ‘predicting’ that a brilliant object will appear shortly in the sky above.

Here are some times to watch for flares in the Duluth area for the coming evenings. Wherever you live, please drop us a line if you spot any.

* Tonight Thursday at 9:44 p.m. 2/3 the way up (59 degrees) in the northeastern sky (azimuth 63 degrees). Iridium 22 satellite.
* Friday July 22 at 9:38 p.m. again in the northeastern sky. Iridium 25. Second flare at 11:13 p.m.  from Iridium 31 27 degrees high (1/3 the way up)  in the northeast.
* Saturday at 9:32 p.m. 61 degrees high in the east-northeast from Iridium 47. This flare will be intensely bright at magnitude -7! A second flare from Iridium 90 at 11:07 p.m. 27 degrees high in the northeast.

8 Responses

  1. Patience

    Hello again astro bob,

    Do you have any information regarding the tenth planet that nasa had found? I read an article at that stated that they had discovered a 10th planet. That also at one point it was visible in the sky in the morning. I believe it was unofficially named Sedna. Thank you

    1. astrobob

      Patience, Sedna is an icy asteroid in the distant Kuiper Belt beyond Neptune, invisible in all but the largest telescopes. It’s about 1,100 miles across. There are other similar-sized asteroids — some larger, some smaller — beyond Neptune. Sorry, it’s not a 10th planet.

      1. Patience

        Oh! Ok. Thank you 🙂 Just wondering why they would call it a planet then? Maybe at the time they had thought it was a planet? I am planning on starting school soon and thinking of maybe taking an astronomy class maybe. 🙂

        1. astrobob

          Patience, it’s possible someone early on thought it should be considered a planet. It’s definitely classified as an asteroid now however. An astronomy class sounds like a great idea. I hope you have the opportunity.

          1. Patience

            Oh ok, thanks astro bob! I enjoy reading your blogs! Thank you I hope so too! I am thinking maybe an astronomy class will help me better understand things that are present in space. Thanks again!

    1. astrobob

      Q of H,
      You filmed the star Sirius. It’s a brilliant white object that twinkles a lot because it’s low in the sky. The twinkles are different colors due to varying pockets of air causing the light to refract continuously. Sometimes you’ll get a red, followed by green or yellow, then blue — every color you can imagine. It’s a common phenomenon and especially noticeable with bright stars in the lower half of the sky where air turbulence is most noticeable.

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