- Published: 18 January 2010
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Anita Abbott, age 13, Charleston, West 'Va.
Why can we see Orion only in winter?
North of the equator, there is always Polaris shining in the night sky, If you watch all night, the whole sky seems to wheel and turn around this constant star. A few constellations make close circles around the Pole Star. These are the familiar Big Dipper, the Little Dipper, Cassiopeia Cepheus and Draco, To us, these are the circumpolar stars. They never rise and set below the horizon, They circle the sky once every 24 hours, though we see them only after dark.
The further north we go, the higher Polaris shines in the sky, At the North Pole it is right overhead. Over Charleston, West Virginia it is between 38 and 39 degrees above the horizon, This means that your home town is between Latitudes 38 and 39 degrees North of the equator, Below 30 degrees in Florida the North Star is so low that most of the Big Dipper rises and sets. At the equator there are no circumpolar constellations circling the sky. All the stars rise and set.
Even our circumpolar stars change with the seasons. Early of a May evening, the pointers of the Big Dipper point down and early of an October evening they point up towards the Pole Star, Further from Polaris are the stars that rise and set. The same time each night finds them a little further towards the west. In late fall, Orion pokes above the horizon during the night. Each night, this most brilliant of all constellations rises a little earlier, By January 1 it is high in the sky by 9 o'clock, Later in the year., it is over in the west, all ready to set by sundown.
Of course, the stars themselves do not travel over our sky in this manner. They seem to do so because of the movements of the earth. The circumpolar stars seem to wheel around each night because the earth is turning on its axis. And one end of the axis points almost directly at Polaris. The seasonal changes are caused by the earth’s journey around the sun. This orbit is a circle 600 million miles around and 186 million miles across, During the year, the earth travels through different parts of the sky. Does this mean that we get different views of the starry heavens? Not at all, the stars are so far away that a difference of a few hundred million miles would hardly show, The real difference is where the earth is in relation to the sun.
Sometimes we are on one side of the sun sometimes on another. Remember we see the stars only at night when we have our backs to the sun, With our backs to the sun in June, we face out towards the constellation Scorpio. The Scorpion is a constellation of summer skies. With our backs to the sun in January, we face out towards glorious Orion. By then we have moved around to where the Scorpion is on the opposite side of the sun. As the earth rotates, this summer constellation comes into our skies with the sun.In summer, we are on the opposite side of the sun from Orion. The starry hunter rises and sets over the sky during the daytime, Yes, Orion passes over our skies every day of the year, though we can only see the beautiful constellation when it appears after dark.