Northern Sky

Northern Sky: February 15-28, 2020

In the second half of February, it doesn’t matter if you’re looking at the post-sunset or the predawn sky; you’re going to see upwardly mobile planets.

In the evening, Venus is still blazing away as a gorgeous evening star. If you look to the west, you won’t have any trouble finding it. As it climbs farther above the horizon, it sets later. Venus is currently up and bright for more than three hours after sunset.

No bright stars are near Venus, but a young crescent moon stops by on the 25th, 26th, and 27th. The moon is way below Venus at first, but on 27th, it’ll have moved to about the same level as Venus. The bright winter stars are in the south after nightfall, so if the night is clear and moonless, don’t miss the chance to see them if you haven’t already. But even Sirius, the brightest of all, can’t match the candlepower of our sister planet. As they say, location is everything.

The three bright outer planets are now assembling in the predawn sky. They’re all fairly low in the southeast, with Mars leading the way—that is, it’s the highest and farthest to the west. Next comes brilliant Jupiter, and finally Saturn. Late in the month, when Saturn is high enough to be easily visible, the three planets form a straight line with Mars at the upper right end, Jupiter in the middle, and Saturn at the lower left end. This assembly sets the stage for some of the closest approaches between these three planets that we’ll ever see, as both Jupiter and Saturn pass Mars.

What’s happening is, Earth’s orbital motion is carrying us closer to all three planets; this pushes them higher and farther west each day. But they don’t move west at the same speed. As they orbit the sun, all the planets move eastward against the background of stars. Because Mars orbits eastward at great speed, it resists Earth’s westward push. But Jupiter and Saturn orbit sluggishly, and so Earth’s motion is pushing them westward, toward Mars, rather fast. In just a few weeks we’ll see first Jupiter, then Saturn, catch up to Mars and pass it.

Also, since Jupiter’s orbital motion eastward is faster than Saturn’s, it’s slowly closing in on the ringed planet. We can watch this slow approach until December, when Jupiter and Saturn pass each other in the evening sky.

In the days leading up to the new moon on the 23rd, a waning the moon plunges through the morning sky, toward the rising sun. On the 18th, the moon passes right in front of Mars. The red planet disappears behind the moon’s bright leading edge, which is to say, behind the lighted crescent. Mars reappears behind the moon’s dark edge, but not until after daylight. If you want to see Mars disappear, get out by 6 a.m. and bring binoculars. This won’t be the most spectacular lunar occultation, as these eclipse-like events are called, because Mars is still pretty far away and small, so don’t feel bad if you miss it.

The next morning, the 19th, a thinner crescent moon will be staring right at Jupiter, and on the 20th an even thinner moon rises below Saturn. Try to catch those two about an hour before sunrise, before Saturn gets washed out.

Also, between the 24th and 25th, Mars glides right above the star that marks the lid of the Teapot of Sagittarius. Meanwhile, Jupiter pretty much stays put below the softly curving Teaspoon of stars. If you’ve never seen these features of Sagittarius, these planets can be your guide.