The Pleasures Of Satellite Watching


I love surprises! By good fortune, my camera caught a nice flare from a passing satellite last night when I was taking a photo of Leo and Mars (right of center). The satellite traveled from right to left below the Backwards Question Mark (outlined) starting out faint, then flaring brightly before fading from view. Photo: Bob King

Have you noticed how many satellites are out now compared to winter? It seemed that everytime I looked up last night one or another crept silently across the stars. The first materialized in Leo’s Tail, another in Hercules, two in the Big Dipper. I was lucky enough to catch a brief, bright glint off another with my camera as it flared to life in Leo near the planet Mars.

The best time to see satellites is during twilight which takes up a good part of the night especially in higher northern latitudes. It’s no surprise then that the number of satellites increases during spring and summer as twilight lengthens. The only requirement for seeing a manmade satellite is for the sun to have set for the observer but not for the orbiting object. During very early twilight, we can see the International Space Station because it’s bright enough to outshine every star, but most satellites don’t come into view until the end of nautical twilight and during the early hours of night.


A replica of Sputnik 1, the first artifical satellite. It was launched into orbit by the Russians on October 4, 1957. One of its purposes was to study the upper atmosphere. Credit: NASA

Since many satellites are hundreds of miles high, they’re like the proverbial mountain peak which still glows in sunlight while it’s dark in the valley below. We see them because they still reflect the sun’s light even though it’s night for us on the ground. Although they can be as large as a football field (the space station), satellites appear starlike because they’re tiny objects many miles away. The space station is the brightest because it’s the largest and reflects more light than any other. Other satellites are spent rocket stages that end up orbiting Earth themselves after propelling surveillance, communication and scientific satellites into orbit. There are defunct satellites, shards and shrapnel from satellite testing or accidental explosions and even a toolbag lost by one of the shuttle astronauts during a space walk. Nuts and bolts abound.

Satellites usually keep a steady brightness as they travel across the sky only fading with increasing distance from the observer or when they eventually enter Earth’s shadow and disappear from view. Other satellites, especially those at the end of their useful lives as well as rocket stages and fragments, tumble about as they orbit. Sunlight hitting their metallic surfaces gets bounced this way and that causing the satellite to flash. If you’ve ever been out at night and seen a short, bright flash that didn’t look like a meteor, it was likely a glint from a tumbling satellite.

One of the most curious of manmade objects is the Japanese EGP (Experimental Geodetic Payload) satellite also known as Ajisai, the Japanese word for hydrangea plant. EGP (at right) is a 7-foot sphere covered in mirrors and reflectors which make it sparkle like a strobe light when viewed through binoculars. I observed it one time and never saw such a "busy" object in the sky in my life. Since it orbits almost four times higher than the space station, the sun rarely sets on EGP so you can see it as late as midnight.

Another group of 66 telecommunications satellites called the Iridium constellation have highly-reflective teflon-coated antennas. When the angle between the observer, satellite and sun is just right, an Iridium can briefly flare, becoming as bright as the quarter moon. I’m not kidding. My daughters and I have seen Iridium flares that made us gasp. You can’t believe something so starlike in appearance can swell to such intensity.

The alignment between the observer, satellite and sun is critical when it comes to flares. An Iridium might be visible only with a 10-mile zone and brightest at a particular spot within that zone. They’re brief too, lasting only about 20 seconds before the little satellite fades back to invisibility. Below is a list of times for evening flares for Duluth. For your town, go to the Heavens Above website, sign in and click the link for Iridium flares for the next seven days. In the table, you’ll see a column called "Intensity" or magnitude. The higher the minus number, the brighter the flare. -4 and above equal or exceed Venus in brightness. Amaze your friends with your prediction that something out of the blue will happen tonight, and then enjoy their reaction when they see their first flare.

* Thursday May 20 at 10:00:31 p.m. Look 2/3 the way up in the northeastern sky for a flare from Iridium 43.
* Friday May 21 at 9:54:29 p.m. Look in the same direction as above. This flare from Iridium 40 will be as bright as Venus.


A brilliant flare from the Iridium 33 satellite taken in 2008. The higher the satellite, the more slowly it moves across the sky. Iridiums orbit 485 miles high so they inch along compared to the space station. Photo: Bob King

Heavens Above is a great site for getting predictions on the visibility of the brightest satellites, but there are numerous software programs if you want to create your own personalized list of viewing targets. Check out the free SatScape, Footprint or WinOrbit.

How to best observe satellites? Kick back on the lawn with your hands cupped behind your head. I remember doing this with my buddies as a teen. We’d talk about everything from life’s tiny details to the big mysteries while watching the space birds fly by.

(EGP photo courtesy of JAXA)