People sometimes complain there’s not enough light in winter. Darn sun never seems to stick around for very long. Yet many of us are starting to notice the increase in the amount of daylight. Today (Jan. 19) the sun lingers over my town for an additional 35 minutes compared to the late December. But who’s counting?
There’s another light in the sky after the sun sets these evenings. I’m not talking about Venus, frankly an amazing sight right now, but the International Space Station (ISS). It’s returned for a round of easy-to-see evening passes now through early February and will make up to two bright flybys each night separated by about 90 minutes.
The station “rises” in the west, opposite the motion of the stars, and “sets” in the east. That’s because it was sent into orbit in the same direction the Earth rotates in order to take advantage of the planet’s rotational speed. For example, from Cape Canaveral in southern Florida, the Earth’s spins at 914 miles an hour (1,471 kph). A rocket launched in the direction of rotation (west to east) gets a free bump of 914 mph. That saves a lot of extra fuel when a rocket is accelerating to reach altitude.
The ISS orbits about 258 miles (415 km) high, traveling at an average velocity of 17,500 mph (25,000 kph). The astronauts have no sensation of this tremendous speed because the craft is moving at a constant velocity, neither slowing down or accelerating, the same way an airplane does when it reaches cruising altitude. That speed is necessary to keep the station in orbit — swinging gracefully around the Earth’s curve — without crashing into the ground.
As the biggest manmade object in orbit the ISS shines brighter than any other satellite. When dimmest it’s about as bright as Sirius the brightest star, and when brightest it rivals Venus. A typical pass, assuming Earth’s shadow doesn’t get in the way, takes about 5-6 minutes. Passes come in seasons with a period of dawn visibility followed by evening passes and ending with daytime-only passes before returning to the dawn sky.
To catch sight of it in the coming nights, go to Heavens Above. Log in, select your city and then click the ISS link on the left side of the page for a 10-day list of passes for your location. Click the pass for the current date and a map and timeline of the station’s path across the sky will pop up.
You can also go to NASA’s super-easy Spot the Station site for times and directions. Sign up to get email or text alerts whenever there’s a favorable pass over your city. Phone apps are even handier. Try ISS Spotter for iPhone or ISS Detector for Android. Both are free, provide times and directions and alert you in advance of favorable passes.
I like seeing the space station go by. I think about the efforts of so many scientists and engineers to put a massive research laboratory into space and keep it running for more than two decades. I also like to picture the astronauts on board (currently six) adding to human knowledge every day by performing diverse experiments and data collecting. And to know that just like you and me they love taking and sharing pictures of the Earth.
Finally, a quick reminder for dawn-risers. The thin lunar crescent, Mars and Antares, the brightest star in Scorpius, will make an attractive group tomorrow morning (Jan. 20) in the southeastern sky at dawn.