JUPITER DOMINANT THROUGH MARCH

Press, Volume CVI, Issue 31307, 1 March 1967, Page 9

JUPITER DOMINANT THROUGH MARCH

Of the five bright planets, Saturn alone will be too close to the sun to be observed during March. The remaining four visual planets, Mercury, Venus, Mars and Jupiter, can all be seen to advantage this month. Before twilight has faded from the evening sky, Venus will be visible as a bnght star-like point low in the west. It will set between 8 p.m. and 8.30 p.m. throughout the month and for this reason will not be high in the sky. To see this planet in its full splendour we shall have to wait until winter when it will set some three hours after the sun.

Jupiter will continue to dominate the evening sky to the north. It rises long before sunset and will cross the meridian in the evening at a point roughly one third of the distance from the northern horizon to the zenith. On March 1 it sets around 2.30 a.m., on March 15 around 1.30 a.m. and on March 31 at midnight Whilst Jupiter will outshine all other celestial objects except the moon, Mars will continue throughout March to increase in brilliance. Its reddish hue will make it an easy object to pick out from the surrounding stars in the constellation Virgo, the Virgin. It rises, slightly north of east at 9.30 p.m. on March 1, around 8.30 p.m. on March 15, and at 7.30 p.m. on March 31. Elusive Mercury

The second half of March will be one of the best times this year to see the elusive planet, Mercury. On March 15 it rises at 5 a.m. and from then until the end of the month rises slightly earlier each morning. On March 31 it rises at 4.15 a.m. From March 26 to April 5 will be the best mornings to look for this planet Then it can be found low in the eastern sky, slightly north of east for almost an hour before dawn in the constellation Aquarius, the Water-bearer. Mercury will exceed in brightness the stars surrounding it. An interesting observation can be made with the unaided eye on the evening of March 21. The moon will then be two days past first quarter, and at 7 p.m. can easily be located in the north-eastern sky despite the bright twilight Five degrees south of the moon will be found the bright planet Jupiter. Five degrees is roughly the distance between the pointers to the Southern Cross. It should be possible, using the moon as a guide, to locate Jupiter before the sun has set. The Southern Cross

No matter how little knowledge one has of astronomy, it is rarely that one finds a person who is unable to recognise the Southern Cross in the sky. More simply termed by astronomers. Crux, The Cross, this constellation is well placed during March. In the early evenings it can be

found to the south-east almost midway between the horizon and the zenith. It appears to be lying on its side with the two bright stars, commonly referred to as the Pointers, lower in the south-eastern sky. Crux is a modem constellation and as a result its main stars do not have proper names such as were bestowed on the bright stars of constellations in the northern sky. Instead they are referred to by the Greek letters of the alphabet under a system of star nomenclature designed by Bayer in 1603. Under this system the brightest star in each constellation is given the letter Alpha, the second brightest is called Beta, and so down through the Greek alphabet in order of decreasing brightness. Occasionally the order of decreasing brightness was not kept to. If one looks on a dark clear night during March when the evenings are still mild, the soft glow of the countless stars of the Milky Way can be seen as a background to the stars of the Cross. But at one spot just below a line joining the two brightest stars of the group appears a dark patch. It conveys the impression of a dark hole in the sky. This is the well known Coal Sack, a region, which, to the unaided eye, appears to have only one star within an oval of about seven degrees. Even with binoculars the region appears devoid of stars although with a moderate sized telescope it reveals tiny points of light These are stars partly hidden by a dark veil. The Coal Sack is formed by gas and dust of a dark nebula which hides the stars beyond. It is estimated that this dark nebula lies at a distance of 600 light years. Colour Differences In the aspect that the Cross presents in the early evenings of March, the brightest star is towards the south and the other principal stars, taken in clockwise order, follow in order of decreasing brightness. It is easy to see that they not only differ from one another in brightness but also in colour. The two brightest, Alpha and Beta Crucis, as well as the fourth brightest, Delta Crucis, appear bluish or bluish white. The third brightest, Gamma Crucis is red whilst the faintest of the five principal stars, Epsilon Crucis is orange coloured. These differences in colour are visible evidence of the wide divergence in the composition of the stars themselves. The bluish stars are huge globes of glowing gas whose surface temperatures range up to 44,000 degress F. The lines of helium are most prominent in their spectra. As a rule, such stars have large masses and mean densities around one tenth that of our Sun. They are fairly distant objects which show a strong concentration along the Milky Way. The orange stars, like Epsilon Crucis, are very much cooler with surface tempera-

tures around 7000 degrees Fahrenheit. The red stars are cooler still, having surface temperatures around 4900 degrees F. They are found widely-scattered in space and are located in all directions. Double Stars

Even a small telescope will reveal other differences between these stars of the Cross. Gamma Crucis will be found to consist, not of a single star, but of two stars, one of which is red and the other yellowish. Alpha Crucis is another example of a double star. It consists of two hot, blue stars of almost equal brightness lying close together. Alpha Centauri, the brightest of the two Pointers to the Cross, is another fine double whose components require 80 years to complete one revolution around the centre of the system. This star is also interesting because it was one of the first to have its distance determined. It is just over four light years away and usually is referred to as the nearest star. Actually there is a faint star close to it, known as Proxima Centauri, which is actually slightly closer to the Solar System. Proxima is a peculiar star because at irregular intervals it flares resulting in short lived but sharp increases in brightness. These flares have been detected both optically and by radio telescopes.