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Constellation of the Month: Canes Venatici, the Hunting Dogs

The official name of the Hunting Dogs was yet another creation of Johannes Hevelius around 1690, but another astronomer wanted it changed. In this area of the sky there are no associated Greek or Roman myths, so Hevelius decided that the herdsman (Bootes) needed hunting dogs (Canes Venatici) to chase the greater and lesser bears (Ursa Major and Ursa Minor) across the sky. He put them right between the bears and herdsman, high in our northern sky.

Click Image for Larger Map

Canes Venatici, the Hunting Dogs, stands between Bootes, the Herdsman, and the Big Bear (Ursa Major) and Little Bear (Ursa Minor). In the June sky, Canes Venatici is north of the overhead point, and in this south-facing view, you must tilt your head back to see Cor Caroli and Chara, the brightest stars in Canes Venatici.

In 1725, Edmund Halley wanted to name this area for King Charles I of England. Charles I had a tumultuous reign, constantly fighting with Parliament while trying to assert the Divine Right of Kings to rule the country as he wished. To make things more difficult, Charles had strong pro-Catholic leanings, in a time of religious strife between Protestants and the Catholics.

The First Civil War (1642-1645) was joined between Charles and the Parliamentarians led by Oliver Cromwell. Charles lost to the Parliamentarians. Instead of sharing power to create a constitutional monarchy, Charles attempted to form an alliance with Scotland, and escaped to the Isle of Man. This started the Second Civil War (1648-1649). Charles again lost to Cromwell. Charles was arrested and tried, with Cromwell as the prosecuting barrister. Charles I was convicted of high treason, and executed on January 30, 1649.

Years later, after the restoration of the English monarchy, Halley looked on Charles I as a martyr for the Catholic faith, and wanted Canes Venatici renamed for the king. The brightest star in this area was the center of the proposed constellation, and he named it the Heart of Charles, or Cor Caroli. While Halley did not get his way for the whole constellation, the new name of Alpha Canes Venaticorum stuck, and on star maps it is still shown as Cor Caroli.

Canes Venatici is on the north end of the Coma Cluster of galaxies. There are over a hundred galaxies accessible to amateur astronomers. Perhaps the most famous is the Whirlpool Galaxy, M51. This is a bright galaxy, with a total magnitude of 8.4. It was discovered by Charles Messier on Oct. 13, 1773, as he was watching a comet move slowly across Canes Venatici. Its companion, NGC 5195, was discovered March 21, 1781. Companion? Yes, this is a pair of galaxies.

These two galaxies are orbiting each other, and some 70 million years ago they passed close together down our line of sight. NGC 1595 is now well behind M51, and is pulling a streamer of gas and stars out of M51. NGC 1595's gravitational pull also induces the formation of the spiral arms of M51, compressing the gas and dust in various areas to cause new stars to form in long streamers, giving shape to the spiral. In the spring of 1845, Lord Rosse discovered M51's pronounced spiral structure, the first finding of the spiral structure of a galaxy.

NGC 1595 in turn suffers from M51's gravitational pull. It has become completely distorted out of shape and is now considered an irregular galaxy. Someday, the two will merge as they spiral toward each other. M51 and its companion are some 37 million light years away from us and are 6.4 by 4.6 minutes of arc across. If you have an opportunity to look at this pair through a telescope, take it. You will not be disappointed!


The Planets for June 2007

This month's lineup of planets is much like last month's; the difference is that Mercury is visible at the beginning of the month, instead of the end. Mercury reaches its greatest distance east of the evening Sun on June 2. After that, Mercury starts back down toward the Sun as it moves between the Earth and Sun on June 28. During the month, Mercury will become dimmer as it becomes more of a crescent and gets larger. On June 15, the Messenger of the Gods will be magnitude 2.3 with a 10.9 second-of-arc disc — a skinny 11-percent-illuminated crescent. Mercury spends the month in the constellation Gemini, setting around 9:15 p.m.

Watch the Skies
(all times MDT)

June 2, 4 a.m. —
Mercury greatest distance east of Sun (23 degrees)

June 5, 4 p.m. —
Jupiter at Opposition

June 8, 5:43 a.m. — Last Quarter Moon

9 p.m. —
Venus greatest distance east of Sun (45 degrees)

June 12, 11 p.m. —
Venus 0.6 degrees north of Beehive star cluster (M44)

June 13, 7 a.m. —
Moon 0.9 degrees north of Pleiades (M45)

June 14, 8:13 p.m. —
New Moon

June 21, 12:06 p.m. —
June Solstice

June 22, 7:15 a.m. —
First Quarter Moon

June 30, 7:49 a.m. —
Full Moon

As June begins, Venus slips out of Gemini and into Cancer, where it stays until June 24 when it enters Leo. Venus is above and left of Mercury, and it changes from gibbous phase to crescent, thinning from 56 to 34 percent illuminated during the month. Venus is magnitude -4.3 on June 15 when it is 25.6 seconds-of-arc across, setting around 11:15 p.m. Toward the end of the month, Venus will be approaching Saturn, but will not reach it until July.

Moving eastward among the stars of western Leo, Saturn continues to move away from Earth. At midmonth, Saturn is magnitude 0.4 with a disc that is 17 seconds-of-arc across. The rings are tilted up 14.2 degrees to our line of sight with the southern face showing. They are 77.0 seconds-of-arc across. The Ringed Planet sets around 11:45 p.m.

Jupiter is in the eastern sky as twilight deepens. It is in opposition (on the opposite side of the Earth from the Sun) on June 5, when it will be the largest, 45.7 seconds-of-arc across. At magnitude -2.6, it will be moving westward in southern Ophiuchus. It sets in the southwest around 5:15 a.m.

The last planet in our lineup is Mars, which rises around 2:45 a.m. in the east-northeast. In Pisces most of the month, Mars just makes it into Aries before the month ends. Mars is still a small 6.0 seconds-of-arc across and shines at magnitude 0.8.

The June Solstice occurs on June 21 at 12:06 p.m. Here in the Northern Hemisphere, summer begins, while winter starts in the Southern Hemisphere. This is our shortest night of the year, so be ready to start observing as it gets dark, and "keep watching the sky"!


An amateur astronomer for more than 35 years, Bert Stevens is co-director of Desert Moon Observatory in Las Cruces.


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