Sometimes it's better to start big and go small. Let the space station be your first step into the wider world of satellite watching.
I love watching the International Space Station (ISS) and never tire of photographing it or sharing views of the spacecraft's tiny, H-shape through the telescope with neighbors and fellow amateurs. Ditto for the flaring Iridiums. But one day I thought about all those other satellites we see crisscrossing the sky while pointing the telescope or waiting for the next Perseid to scorch the air. Shouldn't I get to know a few of those, too?
As of December 31, 2016, there were 1,459 active satellites in orbit and roughly 7,500 inactive ones, including everything from rocket stages that went along for the ride into Earth orbit, to defunct reconnaissance, science, communications, GPS satellites, and associated parts and pieces. And those are just the big birds. While the U.S. Strategic Command tracked 17,852 objects in orbit as of last July, it's estimated there are 170 million pieces of debris smaller than a centimeter (July 2013) buzzing around up there.
Some of the stranger things that ended up in orbit before ultimately burning up in Earth's atmosphere were a glove lost by astronaut Ed White during his 1965 Gemini 4 flight; a portion of the ashes of Gene Roddenberry, creator of Star Trek; and a tool bag that slipped from Heide Stefanyshyn-Piper's grasp while she worked on an ISS solar panel in 2008. Classified as ISS DEB (TOOL BAG) and given the official NORAD ID #33442, it was easy to see in binoculars at magnitude +6.4 before its orbit finally decayed.
To begin working the unplowed ground of lesser known but easy to spot satellites, I asked members of the satellite mailing list, Seesat-l, to share some of their favorite bright and flashing satellites. They graciously forwarded me lists and links, some of which are included at the end this article. A word about "flashers." They're generally out-of-control rocket stages or other debris that tumbles as it orbits. Their metallic surfaces act as mirrors and reflect sunlight in a regular pattern toward the observer.
Others such as Japan's Experimental Geodetic Payload (EGP) are designed to twinkle. The 2.2-meter (7-foot) sphere is covered in mirrors and reflectors that make it sparkle like a strobe light when viewed through binoculars. The recently-launched Russian Mayak, a tetrahedron-shaped reflector, was advertised to out-flare the Iridiums but most of us are still trying to catch any glimpse of it at all. To date, only a few sightings have been reported.
Making a List
I compiled a list of the suggestions, then headed over to one of my go-to sites for tracking the ISS and Iridium satellites, Heavens Above. While there are many great online satellite tracking sites and software prediction programs, I like Heavens Above because of its many options and great maps. To use it, sign in and select your town, then return to the homepage and click on the Daily Predictions for Brighter Satellites link along the left side. You'll be taken to a list of satellites you can filter by magnitude depending on how dark your sky is.
I use toggle for magnitude 4.0 (underneath the drop-down boxes for the date) , which pulls up a list of some 55 satellites for evening viewing. If you're out in the wee hours, select the Morning button. My pre-dawn list currently shows a cornucopia of 125 satellites! Even though I can see down to magnitude 6.0 from my observing site on a moonless night, 4th magnitude is plenty dim for naked-eye satellite tracking. Be aware that the listed brightness is the peak magnitude of the object — for much of its path, it can appear considerably fainter.
That's the main difference between ISS and other satellites. We've gotten so spoiled with its brilliance from start to finish, it's a no-brainer following an entire pass. Every other satellite is much smaller than the ISS and many travel in higher orbits, so we can only follow them across a segment of sky, about one-quarter to one-third of their full path, before they grow too faint.
My quest to track fainter satellites has also taught me that while most show up at their appointed times, there are occasional no-shows. I just move on to the next one my list. Speaking of which, let's return to the Heavens Above list. Clicking the satellite's name will call up a map of its path with minute-by-minute positions marked along that path. Maps are extremely helpful as it's crucial to know just where to look to anticipate a favorite rocket stage's arrival.
Next, prepare a list of good candidates for the time you plan to observe and either have the website handy on your mobile phone or write/print a short description of location and direction of motion. Then head out and enjoy an evening of satellite watching, knowing that some of these birds may be watching you, too.
Want more details about what you're seeing? Click on the Info. link at upper right on the map page for individual satellites.
You'll soon discover that many of the objects are the upper stages of rockets used to send a myriad of Russian Kosmos-series satellites into orbit. These include military reconnaissance, science and lunar probes. NASA and ESA are no slouches, either, when it comes to providing rocket bodies for viewing.
The majority of working satellites and all crewed space stations are in low-Earth orbit (LEO) and range in altitude from about 180 km (111 miles) to 2,000 km (1,243 miles) above Earth. This includes the ISS, Hubble Space Telescope, Earth observation and spy satellites, and the Iridiums. Next most numerous are more than 400 TV, communications, and weather satellites in geosychronous orbit (GEO). These satellites orbit at greater than 36,000 km (22,300 miles) altitude and have orbital periods of 24 hours, the same as Earth's rotation. This lets them "hover" over the same location and provide either a continuous stream of photos of the same region of the planet or serve to relay TV signals around the globe.
A smaller number of satellites, including the Global Positioning Satellites (GPS) that are so helpful in helping me find the nearest ice cream shop, and space environment satellites for measuring radiation effects and space debris, occupy Medium-Earth orbits (MEO) at altitudes from about 2,000 km (1,243 miles) to 36,000 km (22,300 miles).
Find Passes for Any Satellite
All satellites receive a 5-digit NORAD catalog number, which makes it very handy to look any of them up on Heavens Above to determine if they're making passes at you. To use this function, return to the Heavens Above homepage and click on the Satellite Database link. In the box, fill in the NORAD (Spacetrack) number, check the In Earth Orbit Only box, tap enter, and you'll see the satellite at the top of the list. Next, click the Visible Passes link and you're all set.
With a waxing Moon this week and early next, we've got less-than-ideal conditions for tracking fainter satellites. But use the time to make a list of what you'd like to see once the Moon's out of the picture about August 12th. One of the things I liked about learning new satellites was seeing a couple of those I was only familiar with through the data or photos they provide. It also doesn't hurt having first-hand experience with space junk, forever a hot topic in the news. Once you're comfortable, invite friends and family over and share a little bit of space age history. Everybody loves satellites.
Ones to Watch
Here's a list of satellites to get your started on your adventures away from the ISS:
- Lacrosse 5 R/B (rocket body)
- Atlas-Centaur R/B (multiple rocket bodies in orbit)
- Cosmos R/B (multiple rocket bodies in orbit)
- BREEZE-M Debris Tank
- Mayak (good luck!)
- SL-16 R/B (multiple rocket bodies in orbit)
- Tiangong-1 and Tiangong-2 (Chinese prototype space stations, both as bright as magnitude 1.5 )
- The pair of TerraSar-X and Tandem-X
- Hubble Space Telescope / HST (for observers in the southern U.S.)
- Aqua (Terra's counterpart)
- H2-A R/B (rocket body from November 2009 launch of IGS-Optical 3 satellite)
- Cosmo-Skymed 1 (#31598)
- USA 267 (#41334)
- USA 215 (#37162)
- Okean O (#25860)
- You can also pick from Celestrak's List of 100 (or so) Brightest Satellites
- Heavens Above
- Visual Satellite Observer's Homepage — A nice, easy guide to satellites.
- N2YO.com — Satellite tracking site. It automatically recognizes your location. You can then use it to find pass times and ground tracks for more than 18,780 objects. This is a great site to use if the NORAD number doesn't yield results at Heavens Above. Just put the number in the Find a Satellite box and then click 10-day-predictions at left.
- Space-Track.org — Create an account to download the latest orbital elements for use in free satellite tracking software programs.
- Celestrak — Another element download site
- Heavensat — Popular satellite tracking software