THE PLANETS IN SEPTEMBER

Press, Volume XCII, Issue 27752, 1 September 1955, Page 9

THE PLANETS IN SEPTEMBER

[Written for “The Press” by K. W. ROTH\ This is the month when Mercury is in a favourable position in the western evening sky. It sets one hour 53 minutes after the sun at the beginning of the month and more than two hours later during the last three weeks. Particularly at the beginning of the month it is sufficiently bright to catch the eye of the casual observer, as it is brighter than Spica, the first magnitude star in the constellation Virgo, which it approaches and passes on September 22. Mercury is the smallest member of the solar family of planets, only 6 per cent, the size of the earth and about four times as large as our moon. As it is also the planet closest to the sun, it can be seen for a few weeks only every year. In higher latitudes, where the apparent daily orbits of the stars and planets are less inclined to the horizon than in our latitude, Mercury is difficult to find indeed. Copernicus, the founder of our Copernican solar system, living at the high northern latitude of Koenigsberg, complained at his death-bed that he had never seen Mercury. Because of the elusiveness of this planet, little is known about its physical conditions. Probably the climate on Mercury is extremely rigorous, with the greatest temperature variations of all planets. Judging from its low light reflectivity, its surface must be very rough, with mountains higher than the Himalayas. It is too small to retain an atmosphere, and, therefore, rocks exposed to the sun will be hotter than molten lead, but during the night will be colder than anywhere on earth in winter.

Saturn is still in the evening sky, but is losing its prominent position. This is the last month this year when Saturn is placed favourably enough for telescopic observation. It is in the west, much higher than Mercury and Spica, the only two other bright objects in that region of the sky. Saturn sets at 11.45, 10.52 and 10.5 p.m., on September 1, 16, and 30 respectively. Its distance from the earth increases to 1,000,000,000 miles on September 30. By the end of September Jupiter reappears in the north-eastern morning sky, rising 1$ hours before the sun.