PLANETS IN MAY

Press, Volume XCIX, Issue 29192, 30 April 1960, Page 4

PLANETS IN MAY

[By C. S. L. KEAY, University of Canterbury] The giant planet Jupiter is now entering the evening sky and will become more prominent as the month goes on. By the end of the month it will rise only 1 hour 21 minutes after sunset and as it will be getting near to opposition with the sun it will be reaching its brightest magnitude. Late in the evening it may be unmistakeably located low in the sky to the east-south-east. Saturn also is rising before midnight but it is not nearly,as bright or prominent as Jupiter. To locate it one must stay up later and watch the sky directly below Jupiter. It will be betrayed by its orange colour and the fact that it will be brighter than any other nearby star, excepting of course, the. planet Jupiter. The times of rising of these two outer planets on May 1, 15 and 31 respectively are 8.33, 7.34, and 6.25 p.m. for Jupiter and 9.43, 8.47, and 7.42 p.m. for Saturn. Times of rising on intermediate dates may be found by remembering that both planets rise approximately four minutes earlier each night. Mars, Venus and Mercury are still in the early morning sky, although Mercury will soon depart. It will pass close to Venus on the sixth and on the seventeenth will go past the sun to enter the evening sky. Both Mercury and Venus will be very bright at the beginning of the month. They are close together and can be located during morning twilight very low in the sky near where the sun is about to rise. Mars remains in an inconspicuous position in the constellation Pisces. It will not be visible in the evening sky until near the end of the year. Massive Jupiter Returning to Jupiter, which will be the dominating object for evening watchers during the next few months, it is true to say that if astronomers on some other planet revolving about a nearby star have detected our solar system it will be due in the first instance to the presence of Jupiter. Being almost three times more massive than the remaining planets of our solar system lumped together, Jupiter produces the most noticeable gravitational effects on the motion of our sun through space. We have similar situations with the stars 70 Ophiuchi and 61 Cygni: irregularities in the motions of these two stars have revealed the existence of invisible planetary bodies revolving about them. Although the masses of these invisible planets are about 10 times the mass of Jupiter they certainly are more planetary than stellar in nature. Remember that the sun, a fairly light-weight star, is over 1000 times the mass of Jupiter. Thus we already have some evidence for the existence of other planetary systems in nearby regions of our galaxy. But we were examining the detectability of our own solar system from the “outside,” as it were. If the imaginary astronomers we mentioned possessed telescopes only a little more powerful than ours and were situated at the distance of the nearest star they would certainly notice irregularities in the motion of our sun caused by Jupiter. If, as well, their telescopes were of very good optical quality they might almost manage to photograph Jupiter directly. At that distance the sun itself would appear as a bright star of magnitude 0.6 (as bright as the star Achemar which this month is due south at 10 p.m.) whereas Jupiter would be so faint that it would only just be detectable by a 200-inch telescope, were it not for the presence of the sun. Since the sun would appear very close to it, only four seconds of arc .away, the sun's greater brilliance would all but obliterate the light of Jupiter. However, a comparatively small improvement in telescopes could render it visible. Perhaps, as I write, the planetary correspondent of some far distant newspaper is speculating on the nature of the tiny companion of the sun!