Earth spins as it orbits the Sun, and the solar system is orbiting the galactic center. So, if I go outside and look up, in what direction are we heading?
Dale Peterson
Oak View, California
When you gaze up at the constellation Hercules, you are looking out the front window of the spacecraft called Earth. Our planet is hurtling at some 45,000 mph (72,000 km/h) toward the star Lambda (λ) Herculis, which lies about 370 light-years away. (Textbooks often state the bright star Vega, to generalize the direction.)
At this speed (and if Lambda Herculis remained in the same position), it would take some 5.5 million years to reach this point in space; it’s not worth thinking about, so just enjoy the ride.
The Sun, the planets, and all the other flotsam and jetsam that constitute the solar system are so insignificant that we can consider the entire mass a point in space. No matter where you might stand — on the Moon, Jupiter’s Io, Pluto, or any location on Earth — you are still traveling in the same direction.
We accept that our planet spins on its axis once a day almost as a matter of faith. Earth and the Moon gyrate around the Sun, completing a full orbit in approximately 365 days. Our planet experiences many other motions, such as precession and nutation, but none has any impact on the inexorable flight toward Lambda Herculis.
There’s more! The Sun and its attendant bodies slowly bob up and down through the Milky Way’s arm. Our planetary system also orbits the galactic center about every 220 million years. And don’t forget that our galaxy is likely on a collision course with the Andromeda Galaxy (M31). Our entire local cluster of galaxies is also in motion. The best part: no motion sickness.
Raymond Shubinski
Contributing Editor
This question and answer originally appeared in the May 2013 issue.
