Texas Astronomy: Tracking the ISS using Heavens Above


We hope you found our last post about tracking the ISS from Australia an enjoyable read. As promised, here is an in-depth introduction to using the “Heavens Above” website here in the United States.

Heavens-Above is dedicated to the observation and tracking of the ISS, as well as synthetic/man-made radio satellites, and flares from iridium satellites.

The site is simple enough to use. To begin, simply follow the prompts on the homepage to enter your observing location. This will take you to a second page where you will be prompted to search for a place name. You don’t have to be exact – most of the time your town is close enough. For example, type in “Houston” and click on “Search.” Houston, TX, USA will automatically populate. Click on “Update” at the bottom of the page and you’re all set! It’s optional (but very convenient) to create an account with a username and password, which will allow you to store frequently visited places. I have a dozen or so locations linked to my account, so I simply login and click the appropriate location – no need to search! This will be important if, for instance, you decide to change your location from Houston to Galveston, which is an excellent location to view from in clear weather. As another option, you can enter your coordinates and time zone manually if you happen to know them.

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If you are a visual person and would like to listen to an explanation, there is a voiced-over guide on YouTube “How to Track the ISS with Heavens-Above.com”

Now, what can you observe with this information?

International Space Station

How many times does the ISS orbit the Earth in a day? During a 24-hour period, the space station orbits Earth about every 90 minutes, so that means in a 24-hour day, the space station orbits approximately 16 times. It travels at a speed of roughly 17,150 miles per hour…that’s about 5 miles per second! The ISS will look like a bright, steadily moving star as it moves across the sky and visible passes will always occur within an hour or so of sunset or sunrise. This timing is due to the ISS’s location in low Earth orbit and the angle required to reflect the sun’s rays so that we can see it.

Radio Satellites

Radio satellites will appear as a small pinpoint of light traveling across the sky. Obviously, night viewing is required. In relatively dark skies, you won’t have to wait long before you see one of the more than 35,000 satellites (some of which are just “space junk”) now in orbit around Earth zipping across the sky. Several hundred of these satellites, ranging more than 20 feet in length and anywhere from 100 to 400 miles above Earth, can be spotted with the unaided eye.

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Iridium Satellite Flares

Using Heavens-Above, you can search for upcoming iridium flares and get information on their timing, brightness, and altitude. Iridium satellites are communication satellites in orbit around our planet. Currently, there is a system of 66 active satellites and spares covering Earth’s poles, oceans and airways. These satellites allow worldwide voice and data communications using handheld devices such as sat phones, pagers, and integrated transceivers. Clicking on the time of the flare in Heavens-Above will give you more details on the flare and will include a sky chart that you can print out. The sky chart will show which constellations the flare will appear in and at what time. Note that with the brightness ratings, you will see negative numbers (e.g., -5.9) as well as positive numbers (e.g., 0.9). The higher the negative number, the brighter the flare will be.

This is one place you will need to enter your location a bit more accurately. The light reflected by the Iridium satellites projects a fairly narrow path on the Earth’s surface and a few miles difference in location makes a big difference in the apparent brightness of the flare. To add to the challenge, they only last a couple of seconds, so you’ll need an accurate timepiece to make sure you’re looking at the right place in the sky, and at the right time. They are well worth the effort, though – the effect of a bright iridium flare is that of a star suddenly appearing in the sky, lasting a few seconds and then fading away. It’s very impressive!

Just as our fellow amateur astronomers in Australia, you can also use N2YO.com to track Iridium satellites.

Write to us at brazosnightsky@gmail.com if you are successful in seeing the ISS, radio satellites, or iridium flares!

Follow me on Twitter: @TexasAstronomer

Until next time,

Clear Skies!
Leonard Ferguson

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