Skywatchers have the opportunity to see the ISS zip across the sky tonight

Tonight backyard astronomers have the opportunity, weather permitting, to see the International Space Station flies across the sky. The ISS should be easy to spot with the naked eye because it's the third-brightest object in the nighttime sky, and it constantly moves. The ISS will look like an airplane as it passes overhead, but it will be moving much faster.

It's not always easy to see the ISS with the naked eye because it varies in altitude above the ground. However, last night (Saturday) and tonight (Sunday), the ISS is orbiting at an altitude that makes it easier to spot with the unaided eye. For those who want the opportunity to see the ISS pass overhead, you can use NASA's "Spot the Station" website designed specifically to help amateur astronomers view the space station as it passes overhead.

The website is very easy to use and will give you customized viewing instructions specific to your city. If you live in a city, you'll need to find an area without light pollution where it's as dark as possible. When you enter your ZIP Code, the website will tell you a cardinal direction and how many degrees above the horizon to look to be able to see the space station as it passes by.

The chart NASA provides will give you an ideal time to see the ISS in your area, the maximum time the space station will be visible before it drops below the horizon, the elevation measured in degrees, and where in the night sky the ISS will first become visible and where in the night sky it will disappear. NASA also has alerts amateur astronomers can register for to let them know when the ISS will be passing over.