The skies belong to everyone, part two: Mercury, Venus, and Mars

Posted by David Eicher
on Tuesday, May 3, 2011

So you bought a telescope to look at everything the universe has to offer. You’ve explored the various craters and maria of the Moon. What should you look at next?

Photo credit: Donald C. Parker
Why not go after some planets? Seven planets are visible in backyard telescopes. The planet that orbits closest to the Sun, Mercury, is bright but never appears very far from the Sun in the sky. You must always look for it right before sunrise or soon after sunset. Mercury is small and distant enough that binoculars and telescopes show it as just a tiny, orange-colored dot of light in the twilit sky.

Venus, however, is another story. It is both the “morning star” and the “evening star.” Save for the Sun and Moon, Venus is the brightest object in the sky. Its orbit lies inside that of Earth, so it always appears close to the Sun, rarely straying more than 50° — two hand spans — away. Because it orbits between the Sun and Earth, we can observe Venus in different phases of illumination just as we do the Moon.

Mars lies farther away from the Sun than Earth, so it almost always looks “gibbous” or “full.” It is bright and easy to locate, however, and offers small telescopes something that neither Venus nor Mercury can — subtle surface markings. Binoculars show Mars’ ruddy color well, but they don’t provide enough magnification to show its disk. A telescope operating at 75x to 100x is required. Under ideal conditions, a 3- or 4-inch scope shows several dark markings against the creamy orange surface, the most prominent of which is Syrtis Major, a triangular rocky plateau near the martian equator. Also visible at times are the polar caps, although their relatively low contrast demands a keen eye.

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