The International Space Station is the largest man-made object in space and the third brightest object in the sky after the sun and the moon. And if you know where to look, the orbiting laboratory and spacecraft port is easy to spot. You won't even need a telescope.
However, because Earth spins as the ISS orbits it, it's difficult to know when and where to search the sky for the space station.
Luckily, Mission Control at Houston's Johnson Space Center determines potential sighting opportunities for nearly 5,000 locations worldwide as part of its Spot the Station program.
You can sign up for email or text-message alerts to be notified a few hours before the ISS will be passing over your location.
NASA notifies participants of only good sighting opportunities, meaning the ISS will be high enough in the sky to be seen — 40 degrees or more — and be visible for at least a couple of minutes. However, keep in mind that Spot the Station doesn't take local weather conditions into account.
Spot the Station alerts provides information on where to look for the ISS in the night sky, and the height at which the station will appear is given in degrees.
Simply keep in mind that 90 degrees is right above you, and any number below 90 means the station will be located between the horizon and the sky directly above you.
The space station is bright enough to be seen even in the middle of a city, and it will look like a star or airplane moving across the sky.
However, the ISS travels at an average speed of 17,227 miles per hour and makes multiple orbits around the planet daily, so it'll move much faster than a plane.
Depending on sky clarity and the station’s position, viewing opportunities could be as often as a couple times a week or as rare as only once a month.
In addition to NASA's Spot the Station alerts, you can download the ISS Spotter app and set up your own alert schedule.
For further details on catching a glimpse of the space station, check out the ISS AstroViewer. It provides the ISS's exact location 24 hours a day, as well as information on predicted passes, including the station's visual magnitude, or how bright it will appear.
To help you locate the ISS, you can also use an app like Star Walk, which will help you identify constellations and other night-sky features. Simply set the app's clock ahead and follow where the station will be in the sky relative to stars and other markers.
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