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Spot the difference You can see another basic difference between a planet and a star by looking at Venus in binoculars or a telescope. The stars show up only as little pinpricks of light, but Venus shows up as a distinct cir- cle, or disc. Venus (and the other planets) look big- ger than the stars only because they are very much closer to us—only a few tens of millions of miles. The stars look so tiny because they are millions of times further away. In fact they are hundreds of times bigger than the planets. There is also another important differ- ence between the planets and real stars. Real stars are searing hot bodies like the Sun, which give off light of their own. Planets give off no light of their own. They shine because they reflect the light of the Sun.

∆ Seen from the Earth, Mars sometimes appears to travel backwards through the heavens.

Planet–watching The three near planets all look quite differ- ent in the sky. Venus is easiest to spot be- cause it is so bright. It is most familiar as the evening star, which appears in the west just after sunset. But at some times of the year, it can be seen as a morning star in the east just before sunrise. Mercury, too, can be a morning or an evening star. But it is more difficult to see. Mars, on the other hand, is usually found in the dark skies of night. It does not shine brightly all the time. Only when it comes close to Earth does it shine brighter than the stars. Then we can easily recognize it by its reddish color.

∆ Mercury appears in the sky just after sunset as an evening star. It is always seen close to the horizon.

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