The International Space Station’s (ISS) back! It’s returned to the evening sky for northern mid-latitude skywatchers through early June. Because the northern hemisphere is tilted toward the sun this time of year and the space station’s orbit also tilts strongly northward it remains in the sunlight throughout much of the northern loop of its orbit. That means that many locations will see 2-3 passes each evening, the first in twilight with the later ones in a dark sky.
The ISS will always first appear in low in the western sky — either southwest, west or northwest — and travel east, the same direction as Earth rotates. When low the station looks like a bright star, but as it rises higher it brightens. Depending on altitude and viewing angle the flying laboratory can appear nearly as brilliant as Venus. Seen at low altitude in the west the ISS is both farther away (and therefore fainter) but also partially illuminated by the sun like a crescent moon. When the station passes overhead it’s not only closer but its phase has filled out to half or so, making it appear much brighter. When it moves east of overhead it’s still close but now closer to “full moon” phase — fully illuminated by the sun — and therefore brightest.
When most brilliant you’ll also notice the station’s pale yellow color. That’s because the ISS’s giant solar arrays (used to power the station) are insulated with a gold-colored, foil-like material called kapton.
May is a big month for the space station. The astronauts are getting ready for a new Japanese cargo mission and the first Commercial Crew before the end of the month. The resupply craft launches on May 20 and will arrive on May 25. Before the astronauts grab it with the Canadarm2 we’ll probably get an opportunity to see the resupply ship — called HTV-9 — “chase” the ISS around the sky.
HTV-9 will deliver over four tons of food, fuel and supplies including new lithium-ion batteries to finish updating the station’s power systems. On May 27, two days after the arrival of Japan’s HTV-9 resupply ship, the first crew to launch from U.S. soil since 2011 will lift off from Florida to the orbiting lab aboard the SpaceX Crew Dragon vehicle. For years NASA has been partnering with Russia to send astronauts to the station using the Russian Soyuz spacecraft. This is an important milestone.
I’ve written here before about using Heavens Above to find out when you can see the station pass over your house. Just select your location, click the blue ISS link on the left side of the page and get a 10-day table of passes. Click on any pass and a map appears showing the station’s path across the sky. This time I’d like to show you how to use an app to do the same thing. Since I have an iPhone I’ll use the free ISS Spotter app. Android users can use ISS Detector. Click on one of the links below to download and install the app.
As soon as you open up ISS Spotter you’ll get a map called a groundtrack showing the where over the Earth it’s orbiting at that moment. To lock onto the station and see the groundtrack in real time click the lock icon in the upper right corner. Now you can watch the ISS slowly work its way around the world. Fascinating!
Want to be alerted to when that pass is about to occur? Touch the alarm button. How easy is that? I hope you have fun racking up lots of sightings as the warmer nights coax you outside to look up at the sky.