Looking for cool Friday night plans? How about watching the largest spacecraft ever created zip across the sky at 4.76 miles per second?
To make things even better, the weather is expected to be superb. Mostly clear skies will dominate the East Coast, with crisp, refreshing dryness sledging all the way down the Appalachians.
For folks in Florida or Georgia, look to the south-southwest at 7:56 p.m. The space station will arc its way higher over the sky before fading off into the northeast about six minutes later. Farther north, it will be a touch later — 7:58 p.m. in D.C., 7:59 p.m. in New York, and 8 p.m. in Boston. It will be bright enough that folks in well-lit, downtown areas can enjoy the spectacle.
The International Space Station will look like a swiftly moving airplane, although it won’t be blinking. Any light you see does not come from the space station. (After all, it’s not as if it risks hitting any errant deer in space, so the ISS doesn’t have headlights.) Instead, it’s reflected sunlight glinting off the station’s solar panels. Because the International Space Station is so high, it can catch the sunlight even after the sun has set for some on Earth below.
The International Space Station, built in 1998, has made nearly 120,000 orbits. It soars across the sky some 294 miles above Earth. That’s 50 times higher than most commercial airliners fly.
Contrary to popular belief, the space station is not immune to gravity. It feels a lot of gravitational pull toward earth. Being onboard the space station diminishes the force of gravity by only about 10 percent.
But no need to duck and cover; the space station is not going to “fall” down. But it is constantly in free fall. However, its extreme forward speed allows it to “outrun” the distance gravity would have it fall during a given interval, balancing out and maintaining its constant altitude. However, if the ISS were to slow down, it would spiral inward toward Earth.
It’s just like when you were a kid. Remember going outside, tying a rope to a bucket filled with water, and careening it vertically around in circles? If you spin fast enough, the water stays in the bucket. . . . but if you stop spinning, PLOP! That’s because centrifugal (outward) force balances gravitational (downward/inward) force. Of course, in the space station’s case, “down” is relative, simply meaning toward Earth.
Because the International Space Station is so close to Earth, it must travel quite fast to escape falling; that’s why we see it moving across the sky so quickly.
If we want the satellite to remain “locked” with Earth’s rotation, peering down at the same place, we have to go way farther out in space. Eventually, we’ll get to a point where gravity is less, meaning the satellite can travel at a slower forward speed to remain suspended and an angular speed that matches Earth’s rotation rate. What’s this height? 22,236 miles! We call that the height of “geosync.” The GOES weather satellites orbit at that height.
Pretty cool, right? Friday night will offer a great science lesson for the kids, too. So set an alarm on your phone, and keep an eye out for something (sort of) out of this world.
