Cup of Stars

In close proximity to the spring constellation of Corvus the Crow— and associated with it in myth— is the constellation of Crater the Cup (KRAY-turr). Both constellations have a central asterism (recognizable star pattern) that aids us in locating them. The Sail asterism of Corvus is the more prominent of the two. Spotting the goblet-shaped asterism nearby is a bit more challenging.

Many cultures have viewed the pattern found in Crater as a vessel: an urn, a goblet, a water bucket, a pot, a mixing bowl for wine, a bowl, or a cup associated with various gods.

Corvus, Crater, and Hydra in John Flamsteed’s 1729 star atlas
Courtesy of Linda Hall Library of Science, Engineering and Technology

In the Greco-Roman mythological tradition, Corvus, Crater, and adjacent constellation Hydra the Water Snake were intertwined. The crow, sent by the thirsty Apollo to fill a cup with water, was distracted by a fig tree and decided to linger there until the fruit ripened. He returned with a water snake in his claws, claiming it had caused his delay. Apollo saw through the lie and forever banished bird, cup, and water snake to the sky. To the sky!

1) An hour after sunset, face south and locate the Sail asterism of Corvus, just east of the meridian.

Looking south to the Sail of Corvus & the Goblet of Crater
Star maps created with Your Sky

2) The Goblet asterism of Crater lies just west of the Sail. With the Sail oriented upright on its mast, the Goblet appears to be tipping over toward the Sail. Can you spot it? The stars of the Goblet are dimmer than the four Sail stars and similar in brightness to the mast star, Alchiba (ull-kibb-AH). The bowl of the Goblet is larger in area than the Sail.

3) A star at the bottom of the Goblet’s base is the only one with a traditional name. The star on the right is Alkes (ALL-keess), the second brightest star in Crater. Alkes is from the Arabic for wine cup. An orange giant star, Alkes is about 80 times as luminous as our Sun.

Each time I search for the Goblet, it takes me a little while to find it. Just when I’m convinced I won’t be able to make it out, pop, there it is, a generously-sized cup of vintage starlight. So be patient. And when you find it, drink deeply. Salud!

As the Crow Flies

More so than any other star pattern, when I see the defining asterism (recognizable star pattern) of Corvus the Crow flying high in the night sky after sunset, I know that it’s spring.

Corvus (KORR-vuss) is the Latin word for crow or raven. Although it’s hard for us to imagine a crow among the sparse scattering of stars in Corvus, we can see in classical star atlases how the ancients imagined the raucous bird: bending over to peck at Hydra the Water Snake, the constellation that winds below Corvus.

Corvus from Johann Bode's 1801 star atlas
Courtesy of Linda Hall Library of Science, Engineering and Technology

Let’s go outside and stretch our wings.

1) About an hour after your local sunset time, face south. If you don’t know the cardinal directions at your location and you don’t have a compass, make note of where the sun sets on the horizon. That spot is approximately west. Stand with your right shoulder to the west, and you’ll be facing approximately south.

Star maps created with Your Sky

2) You’ll find the constellation of Corvus low in the southern sky, just southwest of the brilliant blue-white star Spica (SPY-kuh) in the constellation Virgo the Maiden. If you don’t know how to locate Spica, read this post.

The five brightest stars in Corvus form the small but distinctive asterism known as the Sail. It looks a bit like the wedge-shaped sail of a Chinese junk, with a bit of mast extending below.

Chinese Junk
Image by Wibean

3) The brightest of the four stars that make up the sail shape is the blue-white giant Gienah. Gienah (JENN-uh) is from the Arabic for wing. Moving counterclockwise around the sail shape, we next come to Algorab. Algorab (ALL-gorr-abb) is from the Arabic for raven. Algorab is a binary system, two stars in orbit around each other, although with the naked eye we see their combined light as one star. Algorab’s component stars are a bright white star and a dim orange one; you should be able to see both with even a modest-sized telescope.

The stars of the Sail asterism in Corvus the Crow

Next in line is the yellow-white giant star Kraz. The meaning of its name is unknown. Finally, where the mast meets the sail is the orange giant Minkar (MINN-kahr), from the Arabic for beak.

Dimmer than the four sail stars, the yellow-white dwarf Alchiba (ull-kibb-AH) marks the bottom of the mast. Alchiba is from the Arabic for tent, a harkening to an earlier Arab tradition that saw the star pattern of Corvus not as a bird but as a tent, important shelter for a desert-dwelling people.

Astronomy Essential: The distance from the Earth to the Sun is about 93 million miles.

Because the Earth’s orbit is elliptical, not circular, its distance from the Sun varies a bit over the course of Earth’s year-long orbit. The average distance, however, is about 93 million miles or 150 million kilometers.

Astronomers use a mathematically calculated constant based on the distance between Earth and Sun and call it one astronomical unit or 1.0 AU. They use this as a unit of measure between objects in our solar system. One astronomical unit works out to be slightly less than the average distance between Earth and Sun; it is equivalent to 92,955,807 miles or 149,597,870 kilometers.

Due to the long distances involved even within our own solar system, expressing distances of objects in miles or kilometers quickly becomes cumbersome, making the AU a compact and useful unit of measurement. We can say, for example, that today Neptune is 29.68 AU’s from Earth. Otherwise, we’d have to say it’s 2,758,928,346.9 miles or 4,440,064,781.6 kilometers from Earth. Either alternative is quite a mouthful.