Hunters, Twins, Bulls and Dogs
By Calvin L. Chrisman
For anyone that keeps track of these things, the Earth passed its closest point to the Sun at 6:50 PM on Wednesday (January 2, 2008). This might make you ask why it’s cold outside if we are closer to the Sun than at any other time in the year. The answer is that the Earth is tipped 23.5 degrees on its axis and the northern hemisphere is tipped away from the Sun at this time of the year. In northern hemisphere summer, the Earth is farther from the Sun, but we are tipped towards it, and thus warmer.
As we enter January, we are presented with a dazzling panorama of bright, beautiful stars. Of the twenty-five brightest stars, eleven are in the winter constellations. They are visible in the evening and night sky at this time of year. The most widely recognized winter constellation is Orion, the hunter. In January, Orion is visible in the southeastern sky by early evening. Most people recognize the three stars that constitute his belt, along with several stars seen as his sword hanging down from the belt. The center “star” is actually the Orion Nebula. It is a star-forming region full of both glowing and dark dust lanes and is an extraordinary sight in a telescope. Orion’s right shoulder (to the left as we look at him) is a red star called Betelgeuse. It is a variable star which changes its intensity over a seven year period, but is the eleventh brightest star at its peak. Orion’s left foot is a blue star called Rigel and is the seventh brightest star in the sky.
Orion is said to be hunting Taurus the bull. Taurus is to the South (right as you look at the sky) of Orion. The head of the bull is represented by a triangle or wedge of stars. Its bright red eye, Aldebaran, is the thirteenth brightest star. In or near this formation are two exquisite open-clusters of stars, the Hyades and the Pleiades. Faint stars like these are sometimes best viewed with what astronomers call “averted vision”. Instead of looking directly at them, look slightly to the side. Your eyes have more dark sensitivity away from the center of the pupil.
Rising behind Orion is the constellation Gemini, the twins. The heads of the twins are represented by Castor (twenty-third brightest) to the right and above red Pollux (seventeenth brightest). In a small telescope with magnification of 100x or greater, Castor will appear to be a double star. Only the largest professional telescopes will show that is actually six stars!
Later in the evening, after 10:00, follow the line of Orion’s belt down toward the horizon and it will lead you to Sirius, the brightest star in the sky. It is in the constellation Canis Major (the big dog) and is known as the Dog Star. Between Sirius and Gemini is another bright star, Procyron, in Canis Minor (the little dog). One legend is that the dogs are helping Orion hunt the bull while another says that they are waiting under the twin’s table for scraps.
While you are looking, don’t forget to take another look at Mars. After its closest approach in December, it is now receding from Earth, but is still quite bright. It is above Orion and behind Taurus. Do not confuse it with Aldebaran.
A final note for January: on the early morning of January 31st, bundle up warmly, get a cup of coffee and go out before dawn. Look to the southeast and you will see Venus and Jupiter (the first and second brightest planets and the third and fourth brightest celestial objects) within 1.2 degrees of one another. They will be even closer together before Dawn on February 1st. It should be a spectacular sight.