Northern Sky: Feb 17 - Mar 2 2018

“Northern Sky” by Deane Morrison  Feb. 17-March 2 2018

In the second half of February, Venus starts to peek out from the sun's afterglow and slowly climb into the evening sky. On Saturday, February 17, there's a thin young crescent moon in the west-southwest, and if you look half an hour after sunset you may spot Venus way below and a little to the right of the moon. In the coming days, the moon will move on to the east, but keep looking in the same spot for Venus, although it will be a little higher each night.
 
As the moon makes its way eastward, it waxes. Between the evenings of the 22nd and 23rd, it passes the bright star Aldebaran, the eye of Taurus, the bull. The evening of the 24th, it travels the night sky above Orion.
 
The moon finally becomes full on Thursday, March 1st, at 6:51 p.m. It'll be big and bright because it'll be just a couple of days past its closest approach to Earth in this lunar cycle. And, since moonrise over Grand Marais comes at 5:32 p.m.--barely more than an hour before perfect fullness--it'll be one of the roundest moons. Also, this gorgeous moon rises against a pale sky opposite a setting sun. It crosses the night sky below the belly of Leo, the lion, a spring constellation.
 
The latter half of February is a good time to watch the predawn show because there’s little interference from the moon. Three planets are all well up by an hour before sunrise, and they form an almost perfectly straight line. Starting low in the southeast and moving diagonally up and to the right, they are Saturn, Mars and Jupiter. Off to the right of Mars is Antares, the bright heart of Scorpius. Antares' name means rival of Mars, and as Mars brightens over the coming months it'll really outshine Antares and even begin to rival Jupiter.
 
Unlike Mars, Jupiter and Saturn don't change much in brightness because they're always very far from Earth no matter where Earth is in its orbit. Therefore, their distance from us can only change by a relatively small amount. But the orbits of Mars and Earth are much closer, and like runners in adjacent lanes on a track, our two planets vary widely in relative distance. As Earth gains on Mars and gets ready to lap it in the race around the sun, we get a lot closer. Mars’s mid-February distance is about 143 million miles; that shrinks to only 36 million miles when we lap it in July.
 
Mars also differs from Saturn and Jupiter in another way that we don’t need a telescope to see. If you watch the planets’ positions with respect to the stars, it looks as though Saturn and Jupiter are barely budging. And why not? Earth’s orbital motion pushes both stars and planets westward. But Mars is budging quite a bit compared to the background of stars, because its orbital motion, eastward, is so much faster than the other outer planets'. Sure, Earth’s motion also pushes Mars westward, but not nearly as fast as it does the background stars, or Jupiter or Saturn. From morning to morning you can watch Mars plowing its way eastward, away from Jupiter and Antares and toward Saturn. In the first week of April, Mars passes Saturn.
 
Also in the predawn sky, the Big Dipper is now hanging high in the west. If you follow the curve of its handle, that brings you to Arcturus, whose name means follower or guardian of the bear. Arcturus is a brilliant star, high to the upper right of Jupiter. Also try finding the crown of Scorpius, which is three stars that now look like a shield protecting Antares from Jupiter.