Serpens, the Serpent
Plus the planets for September.
Last month we highlighted Ophiuchus, the Serpent Bearer. This month, we highlight Serpens, the Serpent that he is holding. Serpens is a unique constellation, the only constellation split into two separate parts — Serpens Caput and Serpens Cauda. Serpens Caput is the Serpent's Head and it is the western part of this constellation. Serpens Cauda is the eastern part of this constellation and forms the Serpent's Tail. The serpent's middle is part of Ophiuchus, so this mythological creature is actually split into three parts.
While Serpens Caput and Serpens Cauda are on either side of Ophiuchus, they are considered a single constellation. As such, they have only one Alpha star, one Beta, etc., known as the Bayer designations and ordered by visual brightness. They also have one set of Flamsteed designations, which are a set of numbers starting with 1 that is assigned by increasing Right Ascension (west to east in the constellation). Collectively, these two constellations are referred to as Serpens.
Serpens is associated with Ophiuchus and while there is no mythological character by that name, Ophiuchus is sometimes identified with Asclepius. Asclepius was an incredible healer, having been raised by the kindly centaur Chiron, who taught him medical healing skills, to the extent that he could bring back the dead. The ruler of the Underworld, Hades, felt this was an encroachment on his realm and complained to Zeus. Growing tired of Hades' complaints, Zeus finally struck Asclepius down with a thunderbolt. Zeus then put him in the sky so he would be remembered. Ophiuchus (Asclepius) and Serpens are now considered the symbol of the healing arts. A serpent wrapped around a rod (the Rod of Asclepius) is a symbol of the medical profession (commonly confused with the caduceus, the staff of Hermes).
There are a number of objects in Serpens, especially in Serpens Caput, which has the Milky Way going through it. But one discovery reported in April 2007 was quite surprising: Astronomers P.G. Tuthill of the University of Sydney and J.P. Lloyd of Cornell University were studying stars in the Mount Wilson Catalog (MWC) of stars that showed emission lines. They were using a relatively new observing system called adaptive optics on the 200-inch Hale telescope on Palomar Mountain in California and on the W.M. Keck Observatory on Mauna Kea in Hawaii.
Adaptive optics (AO) is a technique of changing the optical path of different parts of an image faster than a second to compensate for the changes in the atmosphere the telescope is looking through. This allows much clearer images to be made without the blurring the atmosphere usually introduces into astronomical imaging.
The Red Square Nebula (NASA)
Tuthill and Lloyd were observing the 14th-magnitude Mount Wilson Catalog star number 922 (MWC 922). The resulting image showed nebulosity centered on MWC 922 that looked like a red square, so it was dubbed the Red Square Nebula. It is tiny, barely 15 seconds-of-arc across, and very faint, which is why it was not detected before. The image released to the public was taken in near-infrared light. It was processed to brighten the extremely faint outer regions of the nebula and sharpened to bring out the fine details. The results show one of the most symmetrical objects observed at such a high level of detail.
This is a bipolar nebula consisting of two cones of gas streaming out in opposite directions. The edges of each cone form a 90-degree angle and are curved, rather than pointed, down near the star (hyperbolic curves). We are looking at the Red Square directly side-on. If we were looking at it end-on, it would look more like a ring nebula. Inside the cone opening, sides of the Square are filaments like the teeth on a comb. These are highly unusual, and it is thought these may be caused by periodic ripples in a disk much closer to the star. These ripples cast shadows onto the gas in the cone, forming the comb-teeth pattern.
The Red Square is a very complex nebula that also has rungs or bars running across the cones. MWC 922 is a giant star of class B that is reaching the end of its life and shedding its atmosphere into the surrounding space. One day, this star may explode into a supernova, giving us a completely new nebula and destroying the symmetry of the Red Square Nebula.
The Planets for September
Mercury is still in our evening sky this month. During September, it will drift slowly southward along and about four degrees above the western horizon. It will reach the west-southwestern horizon by month's end, when it will be heading back toward the Sun. This is an extremely poor apparition for the northern hemisphere, with Mercury being hard to find and almost impossible to observe. At midmonth, the Messenger of the Gods will shine at magnitude +0.1 with a disc that is 6.3 seconds-of-arc across and 67% illuminated. It spends the entire month in Virgo, moving slowly eastward through the constellation.
Saturn is getting lower in the west each day, moving very slowly eastward in central Libra, just 24 degrees up in the southwest as it gets dark. It sets around 10 p.m. At midmonth, Saturn's rings are 35.9 seconds-of-arc across and tilted down 21.9 degrees with the northern face showing. Its disc is 15.8 seconds-of-arc across.
Watch the SkiesSept. 2, 5:11 a.m. — First Quarter Moon
Sept. 8, 7:38 p.m. — Full Moon
Sept. 15, 8:05 p.m. — Last Quarter Moon
Sept. 22, 8:29 p.m. — September Equinox; autumn begins in northern hemisphere
Sept. 24, 12:14 a.m. — New Moon
Mars is 26 degrees up in the southwest as it gets dark and sets around 10:30 p.m. Mars is pulling eastward away from Saturn, starting the month in central Libra, crossing the northern panhandle of Scorpius and ending up in western Ophiuchus. At midmonth, the God of War shines at magnitude +0.7 with a disc 6.4 seconds-of-arc across.
Jupiter is moving slowly eastward in eastern Cancer. At midmonth, it rises just before 4 a.m. in the east-northeast, shining at magnitude -1.9. The King of the Planets will be 31 degrees up in the east as it gets light, with a disc 32.7 seconds-of-arc across.
Venus ends its run in the morning sky this month. At the beginning of September, it is just seven degrees up in the east-northeast as it starts to get light, having risen at 5:30 a.m.; its disc is 10.1 seconds-of-arc across and 97% illuminated. Venus starts the month in western Leo, moving quickly eastward. It crosses Leo and ends the month in western Virgo. Venus will be too close to the Sun to see by the middle of the month.
The Sun crosses the celestial equator on Sept. 22 at 8:29 p.m., marking the beginning of astronomical autumn in the northern hemisphere. The Sun will continue traveling southward until December. So take advantage of the increasingly earlier darkness to "keep watching the sky"!
An amateur astronomer for more than 40 years, Bert Stevens is co-director
of Desert Moon Observatory in Las Cruces.