Looking southeast on December 15 at 9:00 p.m.
December night sky
The meandering constellation Eridanus, the River, covers about 1,130 square degrees of sky, making it the sixth-largest constellation. It may be one of the largest, but most of the stars comprising the figure are third and fourth magnitude and fainter, making it difficult to locate.
Eridanus resides in the southeastern part of the sky at about 9:00 p.m. in the month of December. To locate the constellation, start with Rigel, the bright star that is the right foot of Orion. The star just above Rigel is one end of Eridanus. Wend your way from star to star—north, then west, then southeast, and eventually back to the south. The trail of stars eventually takes you down to the southern horizon.
The yellow star Epsilon Eridani in Eridanus is one of our nearest sun-like neighbors, only 10.7 light-years away. Epsilon Eridani is a K-type star, making it slightly cooler and less luminous than the Sun. It has been the subject of several attempts to listen for signs of intelligent radio signals; - none have been heard so far. Some astronomers believe a large planet, or perhaps a small stellar companion, orbits this interesting star, but this has yet to be confirmed. And Star Trek fans may be interested to know that Epsilon Eridani is also the fictional star of Mr. Spock's home planet, Vulcan.
Three hundred light-years away there is another strange object just recently discovered in the constellation Eridanus. It is not a star, a planet, or even a brown dwarf. In fact, astronomers don't know what to call it. At one time, the object was a star. But a companion sucked most of the matter from it, leaving a strange corpse like nothing scientists have seen before. Some five hundred million years ago, this former star burned bright, but it snuggled up too close to a much more massive object, a compact star called a white dwarf.
White dwarfs are stars that are near the end of their existence. They begin as sun-like stars and, after burning up their fuel, collapse into a small ball. The white dwarf is now about 60 percent as massive as the Sun and has collapsed to a diameter about equal to that of Earth.
The mystery object now contains a mere one-twentieth as much material as the Sun and is still inflated to roughly the same diameter as Jupiter, researchers said. (The Sun is one thousand times as massive as Jupiter.) Astronomers believe that both objects were similar to our Sun. The mystery star, when it was still a star, gave most of its material to the dwarf until it had nothing more to give. The objects have always lived close together. Originally, they orbited each other every four or five hours. But their interaction brought them closer together over millions of years. Today, they orbit each other astonishingly fast—once every eighty-one minutes.
The donor star has reached a dead end. It is far too massive to be considered a super-planet. Its composition does not match known brown dwarfs. And it is far too low in mass to be a star. Science has no true category for an object in this type of situation. More observations are planned to see where this duo's dance will end.
NEAT, LINEAR, and Bradfield are names of comets that have graced our night sky this year. Machholz could be the fourth visible comet of 2004. Whether it becomes bright enough to be visible without binoculars is yet to be seen. According to calculations, comet Machholz could become as bright as fourth magnitude (stellar object brightness is measured in magnitude numbers with larger positive numbers being dimmer and negative numbers being very bright). It could possibly stay around at this brightness for about a month beginning right after Christmas.
Under very dark skies, a person should be able to see a sixth-magnitude object. Fourth magnitude means that the comet should at be at least dimly visible to the naked eye in dark skies, though better seen in binoculars or telescopes. City dwellers would not be able to see it without using binoculars or a small telescope.
If you have a small telescope, look for comet Machholz in the constellation Eridanus. During December, the comet will move north of the celestial equator, tracking from southern Taurus on up into the constellation Perseus.
The comet is predicted to come closest to Earth on the night of January 5-6, 2005, when it will be just thirty-two million miles away. On the evening of January 7, it will conveniently pass just a couple of degrees to the west of the famous Pleiades star cluster.
Few celestial events have greater false-alarm potential than comets. As an example of how difficult it is to predict comet brightness, consider NEAT earlier this year. Estimates had this one becoming a first magnitude object, easily seen even with bright city lights. Unfortunately, it only reached third magnitude. But comets do surprise us sometimes and become even brighter than predicted. Hopefully this one will be a good surprise.
Look for most of the planets in the morning southeastern sky this month. Only Saturn is visible in the evening sky.
- Mercury will make an appearance low in the morning twilight. To find it easily, look in the southeast about one hour before sunrise, just above Venus on December 31.
- Venus will also be low on the southeastern horizon all month long. Look for a Venus and Mars conjunction on December 5, one hour before sunrise. Venus will be just above Mars.
- Like Venus, Mars is low in the southeast before sunrise all month.
- Jupiter is higher in the southeast all month long. Find it about thirty degrees above the horizon one hour before sunrise early in the month. The Moon and Jupiter are in conjunction in the pre dawn hours of December 7.
- Look for Saturn in the evening sky. It will rise in the southeast a little after 9:00 p.m. and earlier each evening.
- The new moon is at 6:29 p.m. MST on December 11. The full moon is at 8:07 a.m. MST on the December 26.
If you are adventurous, try locating Venus during the day. On December 9, the crescent Moon and Venus will be close together at sunrise. At around 10:00 a.m., using binoculars, place the Moon in the bottom-right edge of the binocular view. You may be able to spot Venus on the upper left edge. With a telescope, you may be able to see Mars between the Moon and Venus.
I hope that your holidays are happy. Let us all pray for peace on planet Earth. Send questions or comments to me at email@example.com.
Astrophotographs on display
The LodeStar Astronomy Center and The Albuquerque Astronomical Society have announced the opening of the third annual “Astro-Images of New Mexico: Portraits from the Foothills of Space” astrophotography-contest exhibition. The exhibition, a celebration of the unique beauty of the New Mexico sky, features thirty celestial images taken throughout the state of New Mexico by amateur photographers. LodeStar Astronomy Center is in the New Mexico Museum of Natural History and Science in Old Town Albuquerque ,841-5955 or www.lodestar.unm.edu or www.taas.org.