Planets In December

Press, Volume CVII, Issue 31542, 2 December 1967, Page 19

Planets In December

Mercury will be the only bright planet too close to the Sun in December to see. However, one must rise early to view the brilliant Venus in the dawn sky. It rises almost due east at 2.40 a.m. on December 15 and at 2.25 a.m. on December 31. In our latitudes these times are close to those at which the morning twilight first becomes noticeable. Despite this drawback Venus stands out very clearly against the brightening sky. The evening sky is dominated by the red planet, Mars. At sunset it can be found almost due west and about one third of the way from the horizon to the zenith. During September it passes through the constellation Capricornus, the Sea Goat, and both its brightness and strong reddish colour make it conspicuous amongst this group, which lacks bright stars. On December 1 Mars sets at 11.15 p.m., on December 15 at 11 p.m., and on December 31 it 10.30 p.m.

The brilliant Jupiter rises in the north-east at 1 a.m. on December 1; at midnight on December 15 and at 11 p.m. on December 31. It is a brilliant object in the constellation Leo, the Lion, and will be bright enough to cast a gleam of light across water or even to cast a shadow when the observing site is dark. In October Jupiter was very close to the bright star Regulus and since then has moved slowly away from this star. It is still not very far from the star and in the morning sky the two objects will make a striking sight. Jupiter is much better placed now than it has been during the last few years because it is further south. Even in a small telescope bands of

alternative dark and light texture can be seen stretching across the disc. These bands, termed belts for the dark bands and zones for the light, lie parallel to the planet’s equator. From time to time on these there appear spots, both dark and white. There are often festoons of large ovals edging the belts. By timing the successive transits of these objects across the central meridian of the disc it is possible to find the rotation period. Not all objects, even in the same latitude, rotate at the same speed. There are many different currents in the atmosphere of Jupiter which carry these markings across the disc at different speeds. Almost all our knowledge of these vary-

ing rotation periods has come from the devoted study of a small group of amateur observers. Some of this research is now done photographically but in the main it is carried out visually. Saturn remains in a good viewing position throughout December. On December 1 it set at 2.15 a.m.; on December 15 at 1.30 a.m., and bn December 31 at midnight It will be almost on the celestial equator close to the border of the constellation of Cetus, the Whale, and Pisces, the Fishes. For those who are uncertain of these groups a good time to watch for Saturn will be on the evening of December 10. At 10 p.m. that night it will be less than a degree south of the Moon.