Saturday, November 17, 2007
Jimmy Westlake's Celestial News column appears Tuesdays in the Steamboat Today.
Find more columns by Westlake here.
Steamboat Springs Get ready, Mars is coming!
You already may have noticed an unusually bright orange star rising in the northeastern sky at about 9 p.m. But that's no star - it's the Red Planet, Mars, and it's going to be getting even brighter in our sky during the next few weeks. Here's why:
As Earth and Mars race around the sun in their orbits, the Earth always has the inside track, so it's always moving faster than Mars. Consequently, the Earth catches up with Mars from behind and passes it every 780 days. As viewed from Earth, Mars seems to move backward in the sky against the background stars during the few weeks that we are passing it.
This peculiar backward, or retrograde, motion was very difficult for ancient sky watchers to explain because they held firm to the belief that the Earth was motionless and at the center of the universe. Indeed, if one clings to that belief, it is most difficult to explain how a planet can appear to stop, back up in the sky for a few weeks, and then take back off again as if nothing ever happened. The ancient Greeks devised a complicated system of circles whirling in circles in an attempt to explain it, but all of that became ancient history once we realized that the Earth, too, is in motion around the sun. Whenever Earth gains a lap on one of the outer planets, the planet presents the illusion of reversing direction against the starry background.
On Nov. 15, Mars began backtracking through the stars of the constellation Gemini and will actually re-enter the constellation of Taurus the Bull before resuming its forward motion Jan. 30. In the middle of that 11-week stretch, Earth will be as close to Mars as it can be for this cycle. The night of closest approach will be Dec. 19, when the two planets pass within 55 million miles of one another. Five nights later, on Christmas Eve, Mars will lie in opposition to the sun, rising at sunset, remaining visible all night long and setting as the sun rises. This unusual 180-degree alignment of the sun, Earth and Mars is called a "syzygy."
As if to add an exclamation point to this remarkable event, on the night of Dec. 23, the full moon and Mars will rise together, side by side, providing an unforgettable cosmic moment. From some areas north of Colorado, the moon will actually eclipse Mars briefly, but for us, it will just be a near miss.
Mars will not pass this close to the Earth again until 2016.