D e s e r t E x p o s u r e
June
2009
Constellation of the Month: Corvus, the Crow
Among Ptolemy's original 48 constellations you can find Corvus, the Crow. This southern constellation has only 11 stars visible to the naked eye, presenting an incomplete pattern to the observer. Nonetheless, it has its own mythology shared with its neighboring constellations — Crater, the Cup, and Hydra, the Water Snake.
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Corvus, the Crow, is one of the classical constellations. The mythology around this constellation also includes the neighboring constellation of Crater and Hydra. The most interesting galaxy in Corvus is the Antennae Galaxy, actually a pair of galaxies that are in the process of merging together. They can be seen with a moderate-sized telescope. |
Corvus, the raven (or crow), was Apollo's faithful companion. One day, a thirsty Apollo asked Corvus to take his cup (Crater) and fill it with cool refreshing water from a spring on Earth. Grasping the cup, a magnificent double-handed chalice of the type known in Greece as a krater, Corvus flew downward. As he approached the ground, he came across a tree filled with almost-ripe figs. Corvus decided to wait a few days for the fruit to ripen, then ate his fill.
Picking up the cup again, he flew on to the spring where he filled the cup with the cool water. Knowing that Apollo would be angry, Corvus grabbed a nearby water-snake and flew back to Olympus. There the bird told Apollo the water-snake had prevented him from retrieving the water. Apollo was nobody's fool and became very angry. He cast the raven, cup and water-snake into the sky to become Corvus, Crater and Hydra.
On star charts that depict the constellation figures, the crow is shown pecking at the water-snake's coils. The double-handled Crater (cup) is shown tilting toward Corvus, but just out of reach of the thirsty bird. The water-snake in this story (Hydra) also doubles as the creature slain by Hercules as one of his Labors.
Some biblical texts associate this constellation with the crow that Noah first sent out to look for dry land after the flood. The bird never returned, presumably flying as far as it could before falling into the waters and drowning. Seven days later, Noah sent out the dove that finally found dry land and returned to the Ark with a freshly plucked olive leaf.
Hiding among the stars of Corvus is an interacting pair of 11th-magnitude galaxies, NGC 4038 and NGC 4039. This pair is collectively known as the Antennae Galaxy, appearing like the old rabbit-ear antennae used to receive VHF television signals, or the antennae of an insect. Since each galaxy has its own nucleus, each has its own designation. They were both discovered by Friedrich Wilhelm Herschel in 1785.
These galaxies began to merge some 900 million years ago, when they approached each other. Both are part of the NGC 4038 Group of five galaxies, all in the same area of space. NGC 4038 was originally a spiral galaxy and NGC 4039 was a larger barred spiral. Some 600 million years ago, the two passed through each other, triggering a wave of star formation. The gravity of each nucleus is pulling the other nucleus toward it, causing the two nuclei to spiral around each other. With the two nuclei now in mutual orbits, their complex gravity field sometimes reinforcing and sometimes canceling, streams of stars are ejected from both galaxies. These streams eventually formed the "antennae."
Another 400 million years from now the pair will form a single nucleus, with the rest of the material around them forming a single elliptical galaxy. In about 2 billion years, this will likewise happen to our Milky Way Galaxy and our neighbor the Andromeda Galaxy.
The Planets for June 2009
Just over halfway up in our southwestern evening sky, Saturn and its Rings are still in eastern Leo. Moving slowly eastward among these stars, Saturn remains a telescopic target, its Rings 39.9 seconds-of-arc across at midmonth. The Rings are tilted up 3.7 degrees with the southern face showing. The ball of the planet is only 17.4 seconds-of-arc across. Saturn sets around 1 a.m.
Watch the Skies (all times MDT) June 5, 3 p.m.— Venus at greatest elongation west (46 degrees) June 7, 12:12 p.m. — Full Moon June 13, 6 a.m. — Mercury at greatest elongation west (23 degrees) June 15, 4:15 p.m. — Last Quarter Moon June 19, 8 a.m. — Venus 2 degrees south of Mars 11 a.m. — Moon nearest to Venus and Mars June 20, 11:46 p.m. — June Solstice, summer begins June 22, 8 a.m.— Mercury 3 degrees north of Aldebaran 1:35 p.m.— New Moon June 29, 5:28 a.m. — First Quarter Moon |
Jupiter is in Capricornus this month, starting June right at the border with Aquarius. As the month proceeds, Jupiter will move slowly westward farther into Capricornus. Rising around midnight, the King of Planets is magnitude -2.6, and its slowly enlarging disc is now 43.6 seconds-of-arc across.
At the beginning of the month, Venus rises just before Mars, around 3:45 a.m. They are both in Pisces. Mars immediately moves into Aries, as does Venus, on June 9. Venus is moving eastward faster than Mars so, on June 19, it will pass two degrees south of Mars. The 16%-sunlit crescent Moon will be five degrees north of the pair that morning, making a beautiful spectacle. The God of War will be magnitude 1.1, its disc 4.8 seconds-of-arc across. The Goddess of Love will be five magnitudes brighter at -4.2, and its disc will be five times larger at 20.6 seconds-of-arc across. Mars will appear full, while Venus will have a just-past-first-quarter-and-increasing disc look, 56% illuminated. After that date, Mars will rise first, followed by Venus, around 3:15 a.m.
Mercury is the last planet to rise in our morning sky. It will spend the entire month in Taurus, coming out of the Sun's glare early in the month. Mercury reaches greatest elongation west on June 13 at a distance of 23 degrees; its disc will be 8.2 seconds-of-arc across and 37% illuminated. Mercury will shine at magnitude 0.6. On June 22, Mercury will be three degrees north of Aldebaran. By the end of the month, Mercury's almost-full disc will disappear into the morning twilight.
Northern hemisphere summer begins with the June Solstice on June 20 at 11:46 p.m., when the Sun reaches its northernmost declination, almost 23.5 degrees north of the equator. It will be the shortest night of the year, so make the most of the few hours of darkness before the Sun returns to "keep watching the sky"!