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Constellation of the Month: Coma Berenices, Berenice's Hair

Coma Berenices is a faint constellation in our evening sky, made up primarily of fourth- and fifth-magnitude stars. It is named for the tresses of the queen of Egypt in the third century BC, but did not become an official constellation until 1602.

Queen Berenices loved her husband Ptolemy III. She was very fearful that her husband would not return from the war, and vowed to cut off her long, beautiful hair as an offering to Aphrodite should her husband return safely. When Ptolemy III did return home, she kept her word and had her hair barbered. The hair was given to the priests, who put it in the temple of Arsinoe Aphrodite at Zephyrium.

Years later, the queen's locks were stolen from the temple. This distressed the royal couple greatly. The royal astrologer, Conon of Samos, came up with the constellation Coma Berenices to console them. This faint grouping of stars remained an unofficial constellation for centuries, until 1602. In that year, Danish astronomer Tycho Brache was cataloging the sky, using huge mechanical devices that could make very accurate measurements of astronomical positions. When he got to this area, he cataloged the stars as members of Coma Berenices, cementing its existence among the 88 modern constellations.

Watch the Skies
(all times MDT)

July 3, 10:37 a.m.—First Quarter Moon

5:37 p.m.—Earth farthest from the Sun

July 8, 2 a.m.—Antares near the Moon

July 10, 9:02 p.m.—Full Moon

July 17, 1:12 p.m.—Last Quarter Moon

July 20, 3 a.m.—Moon near Pleiades (M45)

July 21, evening—Mars near Regulus,

July 24, 10:31 p.m.—New Moon

Tycho Brache, who is often pictured with a prosthetic golden nose replacing his original one (which he lost in a duel), believed that the science of astronomy could be advanced only with accurate measurements of the position of the stars in the sky. He designed and built his own measuring devices, and with the help of his sister, Sophia, carefully measured the positions of not only stars, but planets and comets as well. Later, his assistant, Johannes Kepler, used Brache's precise measurements to formulate his three laws of planetary motion. These laws still are the basis for the calculation of orbits around the Sun.

Coma Berenices is also the home of the center of the Coma Cluster of galaxies. This massive complex of over 3,000 galaxies is located some 2,200 quadrillion miles away (2,200,000,000,000,000 miles) from us, and is believed to be almost as old as the universe itself. The central 9 quadrillion miles contains a dense, hot cloud of gas, some 200 million degrees Fahrenheit. The gravity from this cloud forms the adhesive that keeps this cluster together.

Galaxies come in two main shapes, elliptical and spiral. Our Milky Way Galaxy is of the spiral type. Most of the galaxies in the Coma Cluster are of the elliptical type. This is because with so many galaxies in such a small area ("only" about 120 quadrillion miles across), they encounter each other fairly frequently. When this happens, the two galaxies often merge. Their spiral arms are torn apart, changing the galaxies from spiral to elliptical, if they were not elliptical already. Remember that a galaxy is actually made up of many individual stars and gas clouds, which are influenced by all the gravitational fields they encounter.

After a merger, the stars settle into new orbits, no longer in the plane of the flat pancake of a spiral galaxy, but each traveling in its own plane around the new galactic nucleus. With such a wide variety of orbital planes, the galaxy assumes an elliptical shape. Almost all of the galaxies in the Coma Cluster are the result of galactic mergers that have already occurred, so they are almost all elliptical galaxies.

 

The Planets for July 2006

July sees three of the naked-eye planets near the Sun. Mercury and Saturn are virtually invisible all month. This leaves Mars, Jupiter and Venus in our sky, with only Jupiter far from the Sun's disc. Mars starts the month in Cancer, but quickly moves into Leo. Only a tiny 3.9 seconds-of-arc across, Mars has faded to almost second magnitude. It passes the bright star Regulus on the 21st, but this may be difficult to see, with Mars very low in the west. By the end of July, Mars will be lost in the Sun's glare.

Jupiter is 44 degrees above the southern horizon as the Sun goes down, setting about 1 a.m. at midmonth. Holding in Libra all month, Jupiter has been drifting westward among the stars and on July 6 it will reach its stationary point, turning around and heading east again. The King of the Planets is magnitude -2.2, and stretches 39.0 seconds-of-arc across.

Venus is sinking slowly toward the morning Sun during the month. Rising just after 4 a.m., the Goddess of Love moves from Taurus into Gemini. At midmonth it is 11.5 seconds-of-arc across, and shines at magnitude -3.9. Venus is 88 percent illuminated and continues to become fuller as it gets ready to go on the other side of the Sun.

Earth will reach its farthest point from the Sun on July 3. With the Earth being in an almost circular orbit, the difference between the closest and farthest point is only about 3.4 percent. This is negligible compared with the effect of the angle the sunlight falls on us from the Winter Solstice to the Summer Solstice (76.7 percent). So enjoy the "coolness" of the distant July Sun 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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