Constellation of the Month: Ophiuchus, the Serpent Holder
The constellation Ophiuchus, the Serpent Holder, is associated with the Greek healer named Aesclepius. This ancient constellation is one of the 48 constellations described by Ptolemy. It has also been known as Serpentarius, a Latin form of its name. This large constellation is made up of second-magnitude stars just over halfway up in our southern sky. When you look at Ophiuchus, you are looking just above the center of our galaxy, located in Sagittarius.
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The story begins with Coronis, Aesclepius' mother, who was being courted by the god Apollo. After a time, Coronis became pregnant with Aesclepius. Returning to Olympus, Apollo left a white crow to watch over Coronis. Being lonely, Coronis eventually fell in love with a mortal, Ischys. The crow flew up to Olympus and told Apollo about Coronis' infidelity. Apollo was furious with Coronis but also with the crow, because it had not immediately pecked out Ischys' eyes. Apollo turned the white crow black, the color they are to this day.
Apollo's sister, Artemis the Huntress, hearing of Coronis' actions, killed her with a quiver full of arrows. Apollo saved his son and named him Aesclepius. Since Apollo had other things to do, he took Aesclepius to Chiron, the kindly and wise Centaur, whom we know today as the nearby constellation Sagittarius. Chiron brought Aesclepius up and taught him the art of medicine. Aesclepius became a gifted healer and even learned to bring people back to life by observing one snake bringing a mix of herbs to a dying snake, which immediately recovered.
Hades, king of the underworld, was so concerned that Aesclepius would start raising the dead and depopulating the underworld that he appealed to Zeus to stop him. Zeus decided that he would deal with this by killing Aesclepius, who had just brought Orion back to life after an accident. Zeus struck Aesclepius with a thunderbolt, killing him instantly. Zeus then put Aesclepius into the sky as the constellation Ophiuchus. One of Aesclepius' descendants was Hippocrates, the great healer and promulgator of the Hippocratic Oath; the two snakes (serpents) climbing the staff of Aesclepius are still the global symbol of a physician.
Ophiuchus is the home of Kepler's Supernova, originally seen on Oct. 9, 1604, by several observers. Johannes Kepler had to wait until the weather cleared in Denmark, and was able to see the supernova for the first time on Oct. 17, 1604. As the telescope would not be invented for another five years, Kepler made a series of naked-eye observations of this supernova. Kepler's Supernova grew brighter than Jupiter in our sky, and continued to be visible for 18 months.
Kepler studied the supernova so extensively that it was subsequently named after him. His book entitled De Stella Nova in Pede Serpentarii (On the New Star in Ophiuchus' Foot) recorded his observations and conjectures on this new star. Galileo used this supernova's appearance to argue against the Aristotelian dogma that the heavens are changeless. This was the last supernova definitively observed in our galaxy, more than 400 years ago. It is believed that the supernova was about a third of the way across the galaxy from us, somewhat above the galactic center.
While there are no spectra of this supernova to confirm it, astronomers believe this was a Type Ia supernova. This type starts with a double (or more) star system. The largest star in the system is not big enough to evolve into a neutron star and goes through the red giant phase to become a white dwarf. When the companion star becomes a red giant, the white dwarf begins to pull gas from the red giant, compressing it onto its surface. The mass of the white dwarf grows until it collapses into a neutron star in a supernova explosion. This is what Kepler observed just before the dawn of the telescopic age.
The Planets for August 2006
Watch the Skies August 2, 2:46 a.m. August 7, evening August 9, 4:54 a.m. August 10, morning August 13, morning August 15, 7:51 p.m. August 21, morning August 23, 1:10 p.m. August 27, morning August 31, 4:56 p.m. |
Mars and Saturn are too near the Sun to be observed in August. Saturn will be back in our morning sky near the end of this month, and Mars late next month. The only planet not near the Sun now is Jupiter, which is in western Libra all month. Jupiter will be dropping lower in the west-southwest each day, being only 27 degrees up shortly after sundown at midmonth. The King of the Planets is magnitude -2.0, and stretches 35.7 seconds-of-arc across at midmonth, shrinking and fading as the Earth pulls away from it.
Venus rises a little after 5 a.m. It starts August in Gemini, sliding through Cancer and then into Leo by month's end, when it will be hard to see as it slips toward the Sun. The Goddess of Love is 10.5 seconds-of-arc across, and shines at magnitude -3.9 with 94 percent of its disc illuminated. Mercury is just below Venus during the month. It was rising toward Venus in July, but now is turning around and both are heading for the Sun. The Messenger of the Gods is magnitude -0.9, and its 72-percent-illuminated disc is only 6.0 seconds-of-arc across at midmonth. During August, Mercury's disc will start as a 22-percent-illuminated crescent, and end as a 99.8-percent-illuminated disc.
Both Mercury and Venus will pass close to Saturn during the last third of August. But the closest approaches will occur when these two are in daylight as each pair sets in our western sky, rendering these approaches invisible. You can see them close together the morning before or after the closest approach. The Perseid meteor shower will also peak on the morning of August 13, but with the three-quarters-full moon in the sky, this will be a poor showing. The Sun is heading south again, so enjoy the slowly cooling evenings, 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.