By Peter Becker
Planets are often seen bunched together, near the Sun. No, they're not trying to huddle together to get warm or pack in a sandy beach to get a tropical tan. It's just that from the Earth's perspective, the orbits of the planets overlap tightly when viewed in the general direction of the Sun.
An excellent example may be seen this month, February 2013. Mercury and Mars are close together low in the west, in the bright but dimming glow of dusk.
Remember, the Solar System can be likened to a vast music record- or compact disc. The Sun occupies the central hole. On a discarded CD, you could take a marking pen and make dots for the planets, at varying distances from the center. Looking from the dot for the Earth, you can envision what happens in the sky, when other planets are far on the other side of the Sun or nearly so. It is more rare that an outer planet is behind the Earth, with Earth between it and the Sun. Such is the case with Jupiter, visible this winter high in the south after dark.
The planets move in concentric paths, although not quite exact circles, and almost on the same plane. When the planets are near together in the sky we say they are in conjunction.
Mercury, as well as Venus, orbit closer to the Sun than Earth, so they are always seen in either the west after sunset or in the east before sunrise. They are never seen in the south at night.
Mars, however, is an outer planet. At this stage in its orbit, Mars is bunching up with Mercury from our line of sight, as it heads around the other side of the Sun and eventually re-emerge in the morning eastern sky.
To see Mercury and Mars this month, find a spot where the western horizon is very low. Look about 45 minutes after sunset. Binoculars will help you pick out the planets through the glow of dusk. A telescope will not show a great amount of detail; looking low in the sky, the air tends to be turbulent and most laden with dust and vapor. You may be able to see that Mercury shows phases like the Moon, not completely lit as seen from our perspective. Mars will appear as a tiny orange-red dot.
The planets are at their closest on Feb. 7 and Feb. 8. After that point, Mercury is higher than Mars. On Feb. 10 you may be able to detect the extremely thin crescent Moon to the lower right. On Feb. 11, the Moon is a thicker crescent, above the planets and easier to see.
If you are viewing from a dark, rural area with no town or city lights to the west, watch as the stars come out, for the very faint Zodiacal Light. Glowing like the Milky Way, the light is from a great band of dust in the Solar System that accompanies the planetary paths. It will appear shaped like a cone, extending up from the west and tilted left.
New Moon is on Feb. 10.
Your notes are welcome at email@example.com.
Keep looking up!