Most accurate from mid-northern latitudes of approximately 36-40 degrees, north;
(e.g. San Francisco, U.S.A. ** Madrid, Spain ** Tokyo, Japan)
Copyright (c) 1995 Pete Harris; **Back to Star Facts Home Page**
Updated for the month of: December 1995
Seven Sparkling Jewels in the NightLate autumn and winter brings a sparkling little group of stars into the night time sky, called the Pleiades (pronounced PLEE-ya-deez). The Pleiades is a star cluster made up of over a hundred stars. The seven most prominent members, visible to the naked eye as a tightly packed little group, and arranged in the shape of a little dipper, give the cluster its nickname: the Seven Sisters. (See beautiful time exposure photo of Pleiades Cluster on Jason Ware's website.) In December, from mid-northern latitudes, the Pleiades comes into view in the eastern sky around 8:30 p.m., crosses almost directly overhead around 10:30 p.m., and continues toward the western horizon setting around 4:00 a.m..
The Pleiades, one of the closest star clusters to our Sun, is about 400 light years away. Its stars are not just an apparent grouping from our angle. They are a star system, held together by mutual gravitational attraction, with its largest members all within a space of about seven light years of each other. On the grand clock of the universe these are baby or adolescent stars, "only" about 50 million years old (our Sun is about 4 1/2 billion years old). They are a "litter" born of the same intersteller cloud of gas, still huddled together until they get older and begin to go their own way in the universe.
The Pleiades is best seen with the naked eye or with binoculars, so that the whole cluster can be seen in one field of view. With a large amateur telescope whisps of nebulosity, like breath on a mirror, can be seen around some of the brighter stars. This is the embryonic remains of the gas cloud of which the cluster was created.
Cassiopeia the QueenLike a giant and slightly squashed letter "M" in the sky, the constellation Cassiopeia, known as the Queen, stands upright during early evening hours in December. As you face north it is almost directly above Polaris, the North Star, around 7:00 p.m.
Cassiopeia was named by the ancient Greeks after a character in Greek mythology. Cassiopeia was married to Cepheus, the King of Ethiopia (who has a constellation of his own, next to Cassiopeia that looks like an upside-down house). When Cassiopeia boasted that her daughter, Andromeda, was more beautiful than the sea nymphs, Neptune became angry and had Andromeda chained to a rock near the home of a terrible sea monster. Just as the monster was about to devour her, along came Persues on the flying horse (stay with me here, we're coming to a conclusion). He was carrying the snaky-haired head of Medusa, a horrible creature that he had slain. The monster turned to stone when he saw the head and Andromeda was saved (whew!).
From mid-northern latitudes Cassiopeia is one of the constellations near the North Star that never sets. As the Earth spins around once every 24 hours, Cassiopeia makes a giant circle around the North Star, going one twenty-fourth of the way around each hour. If you compare it at the same time during each season, it goes one quarter of the way around each season.
Meteor Shower - One of Year's BestOn the night of December 13/14 one of the year's best meteor showers reaches its peak. It's name is the Geminids. During its peak the Geminids will usually produce potentially as many as 50 to 60 "shooting stars" per hour, or about one per minute. Although the peak is December 13/14, increased shooting star activity should be visible from several days before to several days after.
Most meteor showers are best seen after midnight (see Star Facts article for August, 1995, "Meteor Showers and Shooting Stars After Midnight, and Why You Don't Have to Clean the Bugs Off the Rear Windshield" for explanation.) The Geminids is an exception. Due to the angle from which this shower hits the Earth, this shower is best seen before midnight. This is particularly convenient this year because the moon rises around 11:00 p.m. on December 13/14 and its light will then begin interfering with observation of shooting stars.
Watch the Demon Star Get DimmerThe star Algol, meaning "Demon Star", belongs to one category of variable stars called "eclipsing variables". (See Star Facts article for October, 1995 The Mysterious Demon Star Dims...Then Brightens for fuller explanation). Variable stars change their brightness over a period of time. Algol gets dimmer approximately once every 2 days and 20 hours. It stays near its dimmest for about 2 hours, with the entire fading and brightening process lasting about 7 hours.
Algol is best seen beginning in autumn and into early winter. It is found in the northern constellation Perseus. See diagram below for graphical representation of Algol's position relative to Cassiopeia. The easiest way to find it is to face north and locate the constellation Cassiopeia, which looks like a giant and slightly squashed letter "M" in the northern sky. During early evening hours in December the "M" is standing upright above the North Star. Extend the imaginary line from the "M" 's bottom center point to its top right point about 1 1/2 fist widths further (width of closed fist with arm extended) to a region to the upper right of the "M". In this region find a fairly bright star (not quite as bright as the stars that form the "M") in the center of a group of stars with no clear shape, this group is the constellation Persues. Algol is found a little less than 1 fist width above this central star (or above and right of, depending on time of night). Algol, in its bright state is about the same brightness as the central star.
Some of the times during November 1995, when Algol reaches its dimmest point during North American night-time hours, given in Eastern Standard Time, are Nov 1 at 1:35 a.m., Nov 3 at 10:24 p.m., Nov 6 at 7:13 p.m., Nov 18 at 6:28 a.m., Nov 21 at 3:17 a.m., Nov 24 at 12:06 a.m., and Nov 26, at 8:55 p.m. Some other times given in Universal Time (UT), Greenwich England, are Nov 9 at 21:02, Nov 12 at 17:51, Nov 15 at 14:40 and Nov 29 at 22:44
To see Algol's changes in brightness use binoculars to look at it and some of the surrounding stars of similar brightness, one or two nights before the dates of its dimmest points. Make a sketch on a piece of paper with some notes about how it compares with one or two other stars. Then look again around the time of one of its dimmest points. See how the observations compare. At its dimmest, Algol should be about half the brightness that it is most of the time.
Andromeda, "The Great
Galaxy"Andromeda, shown as M31 on star charts, and known as the "Great Galaxy", is a galaxy 2.2 million light years away from the Milky Way, made up of hundreds of billions of stars. It is the furthest object in the universe that can be seen with the unaided eye, although that is only possible from very dark, clear locations. It is quite visible with binoculars or a low power eyepiece on a telescope. (See Star Facts article for September, 1995, The Andromeda Galaxy - the Most Distant Thing Human Eyes Can See" for further description).
Andromeda is best seen beginning in late summer and throughout the autumn. It is found in the constellation that bears its name - Andromeda. The easiest way to find it is to face north and locate the constellation Cassiopeia, which looks like a giant and slightly squashed letter "M" in the sky. During early evening hours in December the "M" is standing upright above the North Star. Using the left half of the "M" as an imaginary arrowhead, go about 1 1/2 fist widths (the width of your clenched fist held up to the sky at arm’s length) in the direction the arrowhead points in. Scan this area with binoculars to find the fuzzy patch of light that is Andromeda. Sweep back and forth over the area until you begin seeing its dim outer regions that give it an oval shape. (See beautiful time-exposure Photo of Andromeda from Jason Ware's home page).
The "Great Square"
Dominates Autumn SkyFour moderately bright stars, called the "Great Square" dominate the evening sky during autumn. The Great Square is easily recognizable because it is surrounded by what appears to be mostly empty sky. During December it is found directly overhead as darkness comes, and moves west as the night goes on.
There are several interesting facts about the Great Square:
- It is actually a rectangle, not a square; but the "Great Rectangle" just doesn't have the same ring to it.
- The Great Square is not actually considered a constellation. It is part of the larger constellation Pegasus (the "Winged Horse" - good luck trying to see a horse). The Great Square is considered an "asterism" - a recognizable pattern in the sky that is part of one or more constellations. (Another example of an asterism is the Big Dipper, which is part of the larger constellation Ursa Major - the Big Bear).
- One of the four stars of the Great Square, the northeast corner, is actually not in Pegasus at all, it is officially in the neighboring constellation Andromeda. So the Great Square of Pegasus, which is really a rectangle, probably should be called the Great Triangle of Pegasus. So much for the geometry discussion.
The Disappearing Rings of SaturnDuring December 1995 Saturn is almost due south as darkness comes. To find it, locate the Great Square of Pegasus (for help with finding it see entry above titled "The 'Great Square' dominates Autumn Sky"). The two stars with the widest spacing in the Great Square face south. Scan about 1 1/2 fist widths in a southerly direction from the middle of those two stars to find Saturn.
About seven years ago the planet Saturn reached its greatest tilt toward the Earth so that a good deal of the surface of its spectacular rings showed to us. Even small telescopes revealed a magnificent view of the rings. Since then, its angle relative to us has been straightening. In 1995 and 1996 the angle of the rings becomes edge-on to Earth on three separate occasions - May 22, 1995; Aug 10, 1995; and Feb 11, 1996. (See Hubble Space Telescope Image of Saturn Ring-Plane Crossing taken Aug. 10, 1995). Since the rings are believed to be only about 1 mile thick, the fully edge-on view causes them to disappear from view. The rings are visible during some of this period and not visible at other times, as they alternate between fully edge-on and slightly off edge-on. During some of the times they are visible they are actually very bright, though thin, because we are looking through the full depth , as opposed to seeing through them. Use a 70 to 100 power eyepiece on a telescope to see them when visible. They protrude on either side of the planet. Look for the shadow of the rings across the middle of the planet. In about seven years from now Saturn will again reach its greatest tilt toward Earth and the rings will once again present a spectacular sight.
The Full MoonThe next full moon occurs on the night of December 6 to 7, 1995. The moon is full when it is on the opposite side of the Earth from the sun, so that the part of the moon that faces us also faces the sun. Therefore, at the time of a full moon, the moon rises in the east at the same time that the sun sets in the west.
The best times to view the moon with binoculars or telescope is definitly not around the times of a full moon. It is during the times when the moon is in the crescent to half moon shape. It is at this time that the shadows on the moon are the longest, making the craters and mountains on the moon more visible and three dimensional. The best place to look is around the areas where the light and dark sides of the moon meet. This dividing line, called the "terminator", is where sunset or sunrise is occuring on the moon, and shadows are the longest.
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