The sky, April 21-28: The Moon and Spica on April 22

Special to, April 21, 2024

Excerpts from weekly Sky&Telescope report.


■ As night descends, look high in the west for Pollux and Castor lined up almost horizontally (depending on your latitude). These two stars, the heads of the Gemini twins, form the top of the enormous Arch of Spring. To their lower left is Procyon, the left end of the Arch. Farther to their lower right is the other end, formed by 2nd-magnitude Menkalinan (Beta Aurigae) and then brilliant Capella.

The whole thing sinks in the west through the evening. It’s the last part of the even larger Winter Hexagon to depart.


■ This evening the Moon, just a day from full, passes 1° or less from Spica for North American skywatchers. Cover the Moon with your fingertip to block its glare. The time of their closest approach, and their separation then, will depend on your location.

Moon passing Spica, April 21-23, 2024

Remember, the Moon in these illustrations is drawn about three times its actual apparent size. Spica will not actually be on its edge!


■ Full Moon (exact at 7:49 p.m. EDT). Now it shines about 12° below Spica as shown above. Three times as far upper left of the Moon is brighter Arcturus.


■ The brightest star sparkling low in the southwest as twilight fades is Sirius, the Dog Star. Two fists above it is Procyon, the Little Dog Star. To their right is orange Betelgeuse, the uppermost shoulder of sinking Orion. The three form the equilateral Winter Triangle.

A little less far to the lower right of Betelgeuse, look for orange Aldebaran, the lurking eye of sinking Taurus.


■ Right after dark, the Sickle of Leo stands upright high in the south. Its bottom star is Regulus, the brightest of Leo. Leo himself is walking westward. The Sickle forms his front leg, chest, mane, and part of his head. His tail tip is Denebola, about two and a half fists left of Regulus.


■ This is the time of year when, as the last of twilight fades away, the dim Little Dipper extends straight to the right from Polaris. High above the end-stars of the Little Dipper’s bowl, you’ll find the end-stars of the Big Dipper’s bowl.

Mars and Saturn low in the dawn, April 27, 2024

Now Saturn and Mars are a little higher and easier in the dawn and 11° apart.


■ Vega, the Summer Star, the zero-magnitude equal of Arcturus, now twinkles low in the northeast after nightfall. . . depending on your latitude. The farther north you are the higher it will be. If you’re in the latitudes of the southern US, you’ll have to wait until a bit later after dark for it to appear.


■ These spring evenings, the long, dim sea serpent Hydra snakes almost level far across the southern sky. Find his head, a rather dim asterism about the width of your thumb at arm’s length, in the southwest. It’s almost halfway from Procyon to Regulus. Left or lower left of Hydra’s head, by about a fist and a half, is orange, 2nd-magnitude Alphard, Hydra’s lonely heart.

Hydra’s dim, irregular body and tail stretch all the way to Libra just risen in the southeast. He carries Crater and Corvus on his back.

Hydra’s star pattern, from forehead to tail-tip, is 95° long. That’s more than a quarter of the way around the celestial sphere. No other constellation does that. Even the star pattern of the river Eridanus is only 66° from end to end.

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