Stars can, of course, be seen right around the Earth. But because the atmosphere scatters the light of the Sun, the sky looks bright y day and dark by night. This means we can see stars only at night, and therefore only one half of all the constellations at any time. However, the position of the Sun in the sky-which is what prevents us from seeing some stars-varies over the course of their year. As the Earth follows it orbit around the Sun, it position in winter is exactly opposite to its position in summer, with the result that the Sun is positioned against a background of the opposite side of the sky relative to the Earth. As a result in winter we see constellations at night that were not visible six months earlier. For example, in the Northern Hemisphere summer the triangle of stars made up of Vega, Altair and Deneb is high in the sky, while the magnificent figure of Orion, with his prominent belt of stars, is visible in the northern winter.
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