The International Space Station (ISS) has a cycle. For a week or more, it only makes passes during daylight hours, so it’s invisible. Then it comes back into view in the morning sky at dawn for a couple weeks then transitions into the evening sky. After a few weeks of evening passes, it begins a new cycle with a return to daylight-only passes.
These clustered passes are caused by station’s orbit rotating about the Earth approximately every two months and complicated by seasonal effects caused by Earth’s changing orientation to the sun during its yearly revolution. This week, as the Expedition 56 crew conducts space research and orbital lab maintenance, the ISS returns to the evening sky, arguably the easiest time to see it for most skywatchers. And with the sun setting much earlier now that on the cusp of the fall equinox, most passes occur between 7 and 9 p.m.
If you have children, take the family out for a look after dinner. Both kids and adults enjoy the sight of the space station as it moves quickly across the sky — it looks like a bright planet set free from the firmament on a beeline for the eastern horizon. The ISS always travels from west to east, from the sunset to the sunrise direction. When first visible low in the west, it’s bright but not overwhelmingly so because it’s still far away. But within a couple minutes, when the station stands highest above the horizon, it shines with a powerful, pale yellow radiance.
There are currently five men and one woman aboard the space station. While waiting for a Japanese resupply ship expected to launch this Saturday, the crew has been busy conducting biological research including ongoing experiments observing physiological changes to humans in space.
You can find the space station and get a map showing its path by using Heavens Above. Click the link, select your city and then tap the ISS link. You’ll get a list of passes for the coming nights. Click on a date to see a map and timeline. Or go to NASA’s super-easy Spot the Station site for times. Lots of people like to use an app like ISS Spotter for iPhone or ISS Detector for Android.
Assuming clear weather, once you know when the ISS is coming by, step outside a few minutes before the pass, allow your eyes to get used to the darkness and look toward the west or sunset direction. The space station will look like a star where there wasn’t one before and slowly brighten as it moves higher in the sky. Sometimes in mid-path, it fades and then disappears. That happens when the station enters Earth’s shadow. Before that it’s high enough to escape the shadow and shine in sunlight when all is dark below.