Observing a Constellation and the Motion of the Stars

If we observe the night sky for a few weeks we will notice that it is constantly changing. The positions of the various constellations and stars as we see them tonight at a particular hour will not be the same at the same time tomorrow. This happens because on any night, at a particular place, the stars constellations 'rises' about 4 minutes earlier than on the previous night. So the night sky at 9 p.m. on January 1 will be the same as at 8.56 p.m. on January 2, or at 8.52 p.m. on January 3, and so on. On January 16 the same star positions will be same at 8.00 p.m. and on January 31 at 7.00 p.m. thus we see that the constellation pattern moves constantly westward. At the end of the year, that is, after 12 months, the sky pattern is again the same as at the beginning.

This apparent westward motion of the constellations is caused by Earth's orbital motion around the Sun. As the earth goes round the sun, the stars on the dark (night) side become visible and those on the day side are blotted out by the Sun. The pattern changes progressively the year round.

An implication of all this is that on any particular date, at a particular hour, the position of the constellations in the night sky as seen from a particular place would be the same irrespective of the year. In other words, the pattern of the stars in the night sky that we see at 10.00 p.m. on june1, 1997, for example, is the same as it was on the night of june1, 1977 and will be on june1, 2017 at the same time.

The following constellations should be clearly visible to the south around 9 p.m. local time in the seasons indicated. Keep in mind that the sky is curved but our computer screens are flat, so those constellations that appear high in our graphics might be over your head. Choose one of the links below to jump to the current season and the constellations you can look for in tonight's sky. If you want to get a preview of the next season's constellations, just stay up later!

Winter Spring Summer Fall

Winter Constellations

The winter sky holds several distinct constellations and many bright stars. Orion the Hunter is easy to spot because of the row of three stars running East to West that make up his belt. A bright star marks each of Orion's shoulders and knees, and a group of stars seems to form a sword hanging from his belt. A curved line of faint stars outline a shield Orion holds high in front of him.

Orion is followed by his dog, Canis Major, the Great Dog. To locate Canis Major, simply follow the line of Orion's Belt to the East until you see a very bright star named Sirius, which marks the dog's nose. Also called the Dog Star, Sirius is the brightest star you can ...