Open star clusters visible with binoculars, the Moon at perigee, and other cool things to look for in the sky this week.
By Michael E. Bakich
Friday, March 3
The Moon is at perigee, the closest point in its orbit around Earth, at 3 a.m. EST. It will then lie 229,324 miles (369,062 kilometers) away. But because the Moon’s orbit is not circular, its distance from Earth varies by some 13 percent. Still, this morning’s perigee is the second farthest during 2017. The only perigee further will occur in September, when the Moon will lie 798 miles (1,284 km) farther away.
Saturday, March 4
Head outdoors around 10:30 p.m. local time and look for the sky’s fourth-brightest star rising in the east. That’s Arcturus (Alpha Boötis), the luminary in the constellation Boötes the Herdsman. The easiest way to find Arcturus is to first find the Big Dipper, which tonight stands high in the northeast. Note that the Dipper’s handle is curved. Follow that curve downward and you’ll come to Arcturus. Because the handle’s curve is also part of a circle called an arc, use the old phrase, “Follow the arc to Arcturus,” to remember how to locate the orange star.
Sunday, March 5
First Quarter Moon occurs at 6:32 a.m. EST. If you watch carefully, you may see the half-lit orb rising in the northeast just past noon local time. Geometrically, First Quarter means the Sun-Earth-Moon angle equals 90°. When this angle, where Earth always represents the vertex, is 0°, we experience New Moon. That’s when the Moon and the Sun line up. At 180°, the Full Moon lies opposite the Sun as we see it and dominates the night. And when the angle is 270°, the Last Quarter Moon rises at midnight and sets 12 hours later.