Loopy Planet

The planet Mars is a bit “loopy” right now. It’s making a loop against the background of stars — the result of Mars’s retrograde motion across the sky.

Most of the time, Mars and the other planets move eastward against the stellar background — the result of their orbital motion around the Sun. Sometimes, though, a planet reverses direction for a while. Its orbital motion is the same — the only change is our viewing angle.

Mars goes into retrograde when Earth passes by it in our smaller, faster orbit around the Sun. It’s like one car passing another on the highway. Seen from the faster car, a vehicle ahead of it seems to be moving forward against the background of buildings and trees. As the faster car passes it, though, the other one briefly appears to be moving backward against the background. It’s not, though — it’s just a matter of perspective.

Earth passed Mars earlier this month, so the Red Planet will move “backwards” for a few more weeks. Many take that as a sign that they ne