Constellation of the Month: Vulpecula, the Fox
When astronomers started to seriously map the skies, they determined that there were sections that were not a part of the classical constellations. One Polish astronomer, Johannes Hevelius (1611-1687), compiled a catalog of 1,564 stars, called the Prodromus Astronomiae. It was actually published by his wife three years after his death. In his catalog, he created seven new constellations, one of which was Vulpecula cum Answer, or the Fox and the Goose. Exactly what Hevelius was thinking of when he came up with this name we will never know, but later astronomers shortened it to just Vulpecula, the Fox.
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Click the image to enlarge the map. Facing south and looking almost overhead, you can find the fourth-magnitude stars that make up our constellation of the month, Vulpecula, the Fox. The planetary nebula M27, the Dumbbell, is located in the bottom part of this constellation. This nebula is named for the two lobes that make it appear as a dumbbell when viewed through a telescope. Vulpecula is in the center of the Summer Triangle asterism, formed by Deneb, Altair and Vega. |
Vulpecula is located just north of Sagitta, the Arrow, and below Cygnus, the Swan. It is composed of faint stars that do not form any particular pattern. Since it was just created some 400 years ago, there is no classical mythology to make the Fox a memorable constellation.
What does make this constellation memorable are two objects it contains: the first pulsar ever discovered, and M27, the Dumbbell Nebula. The pulsar is not visible in binoculars, but M27 is.
The pulsar is called PSR 1919+21, a reference to its location in the sky. Back in 1967, some Cambridge, Mass., astronomers were observing the sky with a radio telescope. They were looking for flickering in the radio signals from quasars, the tremendously bright nuclei of very distant galaxies. As they continued to observe, they found a signal that appeared every 24 hours in their telescope's aperture. What was really unusual about the signal was that it appeared as a series of pulses that came at precise intervals a few seconds apart. A graduate student in astronomy named Jocelyn Bell actually recognized this was a unique signal. She reported her observations to her thesis advisor, Antony Hewish, who at first thought it was just some local interference.
Watch the Skies Oct. 7, 9:13 p.m.—Full Moon Oct. 11, midnight—Moon near Pleiades Oct. 13, 6:26 p.m.—Last Quarter Moon Oct. 21, 11:14 p.m.—New Moon Oct. 25, 8 a.m.—Antares near Moon 4 p.m.—Jupiter near Mercury Oct. 28, 8 a.m.—Jupiter near Mercury Oct. 29, 3:25 p.m.—First Quarter Moon |
The pulses were recorded four minutes earlier each day, a value that every astronomer knows is the result of the revolution of the Earth around the Sun when observing objects outside of our solar system. This forced Hewish to recognize this signal as originating from space. The precise interval between each pulse at first made the astronomers think they had found an interstellar beacon from "little green men." Before any such announcement was made, however, a more natural theory came to be accepted.
According to the new theory, the signal came from a neutron star that formed in a supernova collapse. A neutron star has a powerful magnetic field that focuses a beam of energy so that when the beam points at us, we get a signal. Since the neutron star is massive, it keeps precise time, much like the Earth does, only the "day" on this neutron star in Vulpecula is just seconds long. Since the discovery of PSR 1919+21, many more of these pulsing neutron stars—known as "pulsars," for pulsating radio star—have been found. One of the faster ones spins 30 times a second. Antony Hewish won the Nobel Prize in 1974 for the discovery of the pulsar; his student, Jocelyn Bell, didn't share in the award.
The other notable object in Vulpecula is the magnificent Dumbbell Nebula, M27. This object is also a first: the first planetary nebula to be discovered. First seen by French astronomer Charles Messier in 1764, and logged as object 27 in his catalog, the Dumbbell appears as a fuzzy patch about one-sixth the size of the full Moon. This is the best example of a planetary nebula in our sky. It is estimated to be some seven quadrillion miles away. Planetary nebulae come from the outer atmosphere of red giant stars that are thrown off during certain phase transitions.
The Planets for October 2006
Mercury is making a brief appearance this month in the evening sky. Here in the desert southwest, though, Mercury will not be very visible—low in the west-southwest, just eight degrees above the horizon shortly after sunset, shining at magnitude zero. At mid-month, Mercury will be only 6.5 seconds-of-arc across.
Down near Mercury you can find Jupiter. The two will be only four degrees apart on Wednesday, Oct. 25, and Saturday, Oct. 28. The two planetary passes are from Mercury moving eastward and then turning around and heading westward back toward the Sun. Jupiter will be only magnitude -1.8, and will be 31.6 seconds-of-arc across.
Saturn is still in eastern Leo. With its 29-year orbit, Saturn moves slowly from constellation to constellation. This month the Ringed Planet will rise about 3 a.m. The rings are now 39 seconds-of-arc across, tilted up only 13.1 degrees with the southern face showing. Saturn's disc is 17.2 seconds-of-arc across.
Venus and Mars, our two closest neighbors, are too near the Sun to observe. They will both be coming back in the morning sky in December. Jupiter will also join them later in the month, so get your telescope ready for that eastern exposure observing, 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.