In the Sky This Month

The Sun will cross the celestial equator tomorrow. The crossing marks the vernal equinox, which is the beginning of spring in the northern hemisphere. It also marks the starting point for measuring the length of the year.

The vanishingly thin crescent Moon has a couple of companions after sunset this evening, the planets Venus and Mercury. Venus is the “evening star,” to the right of the Moon. Much-fainter Mercury is about the same distance to the upper right of Venus.

The Owl Nebula stares out from the Big Dipper. It is a set of concentric bubbles of gas blown into space by a dying star. It’s round, and seen through a telescope or in photographs, it has two dark patches that look like an owl’s eyes.

The Moon will be “new” early tomorrow as it crosses the line between Earth and the Sun. It is lost from sight in the Sun’s glare, but should return to view on Sunday, as a thin crescent quite low in the west at sunset.

One of spring’s most prominent stars is Arcturus, in the constellation Bootes, the herdsman. This yellow-orange star rises in the middle of the evening and soars high across the sky during the night.

Cancer, the crab, is well up in the east at nightfall. Although it is part of the zodiac, its stars are dim. The brightest, Beta Cancri, is so faint you may not be able to see it from a suburb, let alone a bright city.

As Earth turns, most stars rise in the east and set in the west. But a few remain visible all night, every night. These stars are called circumpolar, meaning “around the pole.” In ancient Egypt they were known as the eternal stars.

The constellation Leo is in the east as night falls, with Regulus, its leading light, about a third of the way up the sky. Denebola, the lion’s tail, is far to the lower left of Regulus.

If you have access to a dark skywatching site, this is a great evening to look at the Milky Way. It arcs high over the west as night falls, so it’s quite a sight. And the Moon doesn’t rise until the wee hours of the morning, so it won’t spoil the show.

Saturn is in great view early tomorrow. The giant planet looks like a bright golden star to the right of the Moon at dawn. The orange planet Mars is close by.