Spotting particular stars and planets can be tricky, even though they appear to move very slowly through the night sky. Although the International Space Station (ISS) will appear to cruise much faster across the sky, it is still much easier to spot when it passes, as it will appear to move around the same speed as a high flying jumbo jet.
In order to spot the station you will first need to know when it will be passing over your area. NASA has made this very easy by providing a website that simply allows you to choose the city closest to you and lists the times that the ISS will pass overhead in the coming days. You can also sign up for free email alerts on the site. The website will tell you in what part of the sky the station will appear, how long it will be visible, and in what part of the sky it will disappear. It will tell you how high in the sky the station will be in degrees. Ninety degrees is straight up, while any number lower than that will be between there and the horizon. According to Earthsky.com, if you hold your fist out at arm's length towards the horizon, that is about ten degrees.
Tonight (8/19/15) the ISS will be visible over the Tucson area. According to NASA, the space station will be visible at 8:52 PM for 1 minute. It will appear in the northwest sky and disappear in the same general area, so that should be an easy one to spot. According to NASA, the space station will be around forty-seven degrees at its highest point, which is essentially directly in between the horizon and directly overhead. It should look like a very bright star (brighter than any others in the sky) moving slowly through the sky.
What you are actually seeing is the reflection of the sun off of the solar panels on the space station, which is pictured here below.
Photo Credit: NASA
The space station travels at an average speed of a little over 17,000 miles per hour and orbits on average around 220 miles above the surface. If you can't catch it tonight, there will be several more chances in the weeks ahead.