D e s e r t E x p o s u r e
November
2008
Constellation of the Month: Sculptor, the Sculptor
Another of the southern constellations named by Frenchman Nicolas Louis de Lacaille was originally called L'Atelier du Sculpteur, or in English, Workshop of the Sculptor. Later, the name was shortened to just Sculptor. This constellation was formed from a group of stars first charted by de Lacaille on his visit to the Cape of Good Hope in South Africa, in 1751 and 1752.
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Click the image for a larger map
Rising in the south-southeast, the constellation Sculptor contains few
bright stars, since we are looking through the thinnest portion of the
Milky Way Galaxy. On the chart, SGP marks the South Galactic Pole. Also
in Sculptor in the Sculptor Dwarf Galaxy, a tiny companion of our Milky
Way Galaxy. |
Fellow French astronomer Lalande said that, during a comparatively short life, de Lacaille had made more observations and calculations than all the astronomers of his time put together. In 1961, La Caille crater on the Moon was named for him, as was Minor Planet (asteroid) 9135 Lacaille, which was discovered on Oct. 17, 1960, at Palomar Observatory.
Sculptor is a minor constellation, with no stars brighter than third magnitude. The brightest star is Alpha Sculptoris, a variable star with a magnitude of only 4.3. The nearest star in Sculptor is Theta Sculptoris, only 71.1 light years away, shining at magnitude 5.2. But it is not the stars in Sculptor that are interesting — it's the galaxies.
The nearest galaxy in Sculptor is our own Milky Way. The south galactic pole can be found in Sculptor, so by looking at Sculptor we are looking directly down, galactically speaking. If you think of our galaxy as a pancake, we are about two-thirds of the way out from the center, and looking toward Sculptor is looking straight down from inside the pancake. There is very little of the pancake (the Milky Way) to look through, which explains the scarcity of stars in this region.
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Dim constellation Sculptor rises over
the bright lights of Las Cruces and El Paso as seen from
City of Rocks State Park. Lost in space? The brightest
star in Pisces Austinus, Fomalhaut, is at upper right. (Photo by David Cortner) |
Beyond the Milky Way, the nearest galaxy in Sculptor is the Sculptor Dwarf Galaxy. This was the first dwarf galaxy to be discovered. Harlow Shapley, using photographic plates from the 24-inch survey telescope at Boyden Observatory in South Africa, was the first to recognize the Sculptor Dwarf as a new type of galaxy. In some ways it looks like a globular cluster, with each star individually observable, but the dwarf galaxy is much larger.
Dwarf galaxies are either round or elliptically shaped. They are similar to irregular galaxies, but they have very little gas and no recent star formation. They are essentially dying galaxies. Virtually all dwarf galaxies are orbiting larger "normal" galaxies, just as the Sculptor Dwarf orbits the Milky Way. Dwarf galaxies have also been discovered around the Andromeda Galaxy (M31). There are probably many others, but since their surface brightness is so low, it is hard to see them around more distant galaxies.
Some astronomers have suggested that dwarf galaxies are just giant globular clusters, but there is one big difference: In globular clusters, the stars orbit the center of the cluster, as you would expect based on the mass of the cluster implied by its total brightness of all the visible stars. The stars in the dwarf galaxy, on the other hand, act as though there is much more mass in the dwarf galaxy than we can account for just by looking at the amount of light from its visible stars.
Astronomers believe that the extra mass comes from "dark matter." This is matter that has mass and gravity, but does not reflect or emit light, so we cannot see it. A dwarf galaxy has a great deal of dark matter, a much higher percentage than a normal galaxy. There is almost no dark matter in a globular cluster, making it very different from a dwarf galaxy.
What is dark matter? No one knows. But the effects of its mass cannot be denied. There is five times as much dark matter in the universe as there is normal matter. Even more interesting, there is also "dark energy" and there is even more of that than dark matter.
The Planets for November 2008
Mars will be too close to the Sun to view for the rest of the year. Venus is climbing higher in our evening sky. It is the first "star" to appear each evening, followed by Jupiter. Venus is moving much more rapidly eastward than Jupiter, and Venus will pass it on the first day of December. Venus starts the month in southern Ophiuchus and moves quickly into Sagittarius for the rest of the month. At mid-month, Venus is magnitude -4.1, with the disc 15.0 seconds-of-arc across and a slowly diminishing 74 percent illuminated. Venus sets around 7:30 p.m.
Watch the Skies
(all times MST)
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Jupiter has moved to the southwestern sky, still in Sagittarius. Jupiter is moving lower in the sky and so is becoming harder to observe. Shining at magnitude -2.1, Jupiter is 35.0 seconds-of-arc across at mid-month and sets around 8:50 p.m.
The Ringed Planet graces our morning sky, rising around 1:30 a.m. Saturn is in eastern Leo, moving slowly eastward. It is already east of Leo's rear paws and will continue moving away from the Lion. The rings are slowly closing, but we can still see their southern face. They are tilted up a mere 1.5 degrees, but are still 38.5 seconds-of-arc across. Saturn's disc is 17.0 seconds-of-arc across.
Last to come up is Mercury, which starts the month in Virgo near the star Spica. Mercury rapidly moves into Libra and then across the northern panhandle of Scorpius, ending the month on the western edge of Ophiuchus. Mercury will be visible only for the first week of November in the bright morning twilight. On Nov. 1, it will be 86 percent illuminated and 5.5 seconds-of-arc across at magnitude -0.9. It will continue to become fuller until it passes the Sun in superior conjunction on Nov. 25.
Daylight Savings Time ends on the morning of Nov. 2. On the morning of Nov. 17, pieces of Comet Tempel-Tuttle will hit our atmosphere as the Leonid meteor shower. Unfortunately, light from the waning gibbous Moon will blot out all but the brightest meteors. So if you are a die-hard meteor watcher, wear your heavy coat 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.