There were two other underpasses this year, occurring on April 17 and Feb. "On average, ISS underflights seem to happen a few times a year," Gartley told NASA's Earth Observatory. Known as an " underflight," it is relatively rare for the ISS and Landsat 8's paths to cross, according to Michael Gartley, a scientist at the Rochester Institute of Technology. It is an angle which increases from the north in a clockwise direction, therefore 0º corresponds to North, 90º is East, 180º is South and 270º is West.Credit: Jesse Allen/NASA Earth Observatory If the object is below the horizon then the altitude is negative.Īzimuth: This tells you in which direction to look to find a celestial body and is expressed in degrees or points of the compass. So 0º altitude is exactly on your local horizon and 90º degrees at the zenith or straight up. We are not all astronomers - although being able to spot the ISS may wet our appetites for star gazing - so if you have difficulty with some of the terminology on the site click on the words in blue or check the definitions given below.Īltitude (astronomical) or elevation: Altitude used in its astronomical sense means the angle up from the horizon.
If it is visible the site will give you a star map showing where the ISS is, its path over the sky and the exact time when it can be seen. To find out whether the ISS is visible from where you live visit and fill in the name of your town. The best time for ISS-gazing is just before dawn or just after sunset, when the observer is in the dark but the ISS is in the sun. The ISS passes over most points on Earth every day but cannot always be seen. Although the ISS travels at a speed of 7.7 km per second it is in one of the lowest orbits possible - an approximate 390 km above our heads - and thanks to its large solar wings it is one of the brightest ‘stars’ making it fairly easy to distinguish as it visibly moves across the night sky. Spotting the ISS with the naked eye is not as difficult as it might seem - providing you know in which direction to look.
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