Minnesota Star Watch: Venus, Jupiter dance

Published 7:01 am Sunday, April 26, 2015

By Deane Morrison

Against a backdrop of brightening May twilight, Venus and Jupiter enter the most dramatic phase of a months-long evening dance.

On May Day, nightfall finds Jupiter high in the southwest, just east of the Gemini twins, while Venus blazes away in the west. These planets are the two brightest objects in the evening sky, and their approach throughout the month will be easy to follow.

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Jupiter does most of the moving. It is dropping toward the sunset as Earth leaves it behind in the orbital race. For now, however, Venus stays high above the horizon as the winter stars stream past, carrying Jupiter with them. During May, the stars of Gemini flow by Venus and the distance between Venus and Jupiter drops from 50 degrees to 20. The two planets end the month facing each other across the dim stars of Cancer; at the end of June they finally meet.

As Earth leaves Jupiter in the dust, it catches up to Saturn. On the 22nd, Earth sails directly between the ringed planet and the sun, an event called opposition because it places the planet directly opposite the sun in the sky. That evening Saturn rises in the east, close to Scorpius, and stays up all night. The best time to see it will be 12:30-1 a.m. on the 23rd, after the waxing crescent moon will have set.

Not only will Saturn be bright, but its rings are very favorably tilted for views with a small telescope. Compare its soft golden color to the ruddy hue of Antares, the heart of the scorpion, just southeast of the planet.

While you’re admiring Saturn, look high above it to find the bright star Arcturus, in Bootes, a kite-shaped constellation representing a herdsman or ploughman. Arcturus ranks as the fourth brightest star in the night sky, after Sirius, Canopus and Alpha Centauri. If it’s up, you can find it by extending the curve of the Big Dipper’s handle, or “arc to Arcturus.” It’s a mere 36.7 light-years away and is also one of the fastest-moving stars with respect to our solar system.

Stars in the Milky Way generally orbit within the plane of the galactic disk, but Arcturus’s motion departs radically from the norm: Dropping almost perpendicularly, it’s slicing right through the disk. More than four dozen other stars travel along with it in a flow called the Arcturus Stream. Because of the direction and speed of this motion, Arcturus will be lost to view relatively quickly—but luckily for us, still not for millions of years.

May’s full moon will be another beauty. It reaches fullness at 10:42 p.m. on the 3rd, less than three hours after moonrise. Algonquin tribes called this moon the flower moon, and also the corn planting moon and the milk moon.