GLORY OF THE STARS.

New Zealand Herald, Volume LXV, Issue 19859, 1 February 1928, Page 14

GLORY OF THE STARS.

THE HEAVENS AN FEBRUARY. INTERESTING PHENOMENA. PLANETS AND CONSTELLATIONS. BY CRUX AUSTRALIS. The Sun is in the constellation Capricornus until February 16, when it enters Aquarius. Its apparent altitude at Auckland decreases from 70deg. on the first to 61deg. on the 29th. A splendid sunspot, visible to the naked eye, was on the Sun during the early part of last month. Sunspot activity has been well maintained. The Moon in the course of its monthly journey through the constellations will be in conjunction with Saturn on the morning of the 16th, with Mars and Venus on the morning of the 19th, -with Mercury on the morning of the 22nd, and with Jupiter on the morning of the 24th. Mercury will reach its greatest elongation of 18deg.. from the Sun on the 9th, and will be in Aquarius, visible in the evening sky shortly after sunset. By the 24th it will be at inferior conjunction, lying between the Sun and Earth, and therefore invisible in its rays. Venus is still a brilliant morning star in Sagittarius, from which it will move into Capricornus on the 21st. On the 14th, at 2.30 p.m., it will be in conjunction with Mars, and the two may be viewed close together in the morning sky on that dav. The ruddy planet Mars is now coming into view once more after being for a long time unfavourably placed for observation. It is situated in the morning sky in the constellation Sagittarius. Jupiter is now drawing near to the Sun in the evening sky, being still in the constellation Pisces. Transits, eclipses and occultations of its satellites are now much rarer, owing to the short time the planet remains visible. Such phenomena occur on February 5. 6, 14, 15, 21, and 22. # . Saturn is now a morning star m Ophiuclnis, but . still rather close to the Run for observation. For several years now its splendid ring system will be fully opened out, presenting a magnificent spectacle in the telescope. The Constellation Positions. For February the positions of the constellations may bo found as given below for 11 p.m. of the Ist, 10 p-ni. of the 15th, and 9,p.m. of the 29th. Looking north, Gemini, containing the bright Castor and Pollux, is now well up m the sky. To the west Auripa is now setting," while over this is Taurus, in which the splendid star clusters of the Hvades and Pleiades are never-failing sources of interest. Orion is still prominent slierhtlv to the west of the meridian and above Gemini and Auriga. South of Orion is Canis Major, in which shines Ririus. the brightest of the fixed stars. Between Sinus and Gemini is Canis Minor and Procyon, its brightest member. Rising in the east is Regulus, of the constellation Leo, forming one of a string of stars known as the sickle. Between Gemini and Leo is Cancer, in which the cluster of stars, the Beehive, appears to the naked eye as a large, hary spot. Over Leo and straggling to the southeast horizon is Hydra. Cetus is setting in the west, with Eridanus above, _ and flowing in a stream of stars to its bright est. Achernar, in the south-west. The Southern Cross is now w;ell up in the south-eastern skv. Below it is the larce constellation of Centnurus, with its brilliant Pointers, the brightest of which is the nearest neighbour of the. solar system. Between the Cross and Sirius is the large constellation Arco, containing the brilliant Canopus. The Milkv Way is running north and south, a little to the east of the meridian. The Nature of Comets. A typical comet is made up of three parts —nucleus, coma and tail. Some comets, mainly faint telscopic ones, have only a coma,- the nucleus and tail being lacking. As the comet draws near to the sun it gains in brightness, the coma becomes more contracted, and generally a tail develops, which is expelled from the nucleus in a direction opposite to the Sun It is probable that the tail is formed bv some unknown repulsive force radiated both by the nucleus and the Sun. In some comets near the time of their nearest approach to the Sun a small tail is directed sunward, but this is always very small and is generally doubled over on 'itself in a fan-shaped form, as though the energy with which it was ejected was not sufficient to overcome the Sun's repulsive force. The head of a great comet is brilliant, and sometimes starlike, as was the case in the recent visitor to these skies, but it is the tail which often takes on the most impressive appearance, and invariably excites the wonder and admiration of the " man in the street." Some comets possess tails running "like a road through the constellations.' Others have tails curved like scimitars, fan-shaped, or multiple. The great comet of 1744 had no less than six tails, any one of which would have been sufficient to render it. noteworthy. The tail, however, is by no means always the same- In some comets it has been known to vary rapidly. Donati's comet of 1858 was an instance of this. At one time the tail was broad, with a bright and curving edge. Later, it was like a scimitar, and then it became duplex. A tail does not last throughout the life of a comet. For the greater part of the time it is non-existent, but when the comet, is making its periodical approaches to the neighbourhood of the Sun the tail is formed, by some peculiar solar radiation, and it rapidly grows in magnificence as the distance between the comet and its primary grows less, until, in some cases, the tail when most developed, may bo many millions of miles long and several million miles across at its widest part. Constitution and Mass. Theories of the constitution of comets vary, particularly as. to the mass involvedThe most prevalent opinion current among astronomers is that a comet's mass is almost nothing. Two types of observation serve to confirm this assumption. The first is that co-nets in making near approaches to planets or their satellites fail to exert, a gravitational, attraction sufficient to appreciably disturb their motions. On the other hand, the planets have been known to so alter the orbits of certain comets as to convert them from parabolas to ellipses, so that from being but chance visitors, they become periodic, and we may expect them to reappear at definite intervals. The second observational check on our assumptions as to cometary mass is afforded on those occasions when a comet passes in front of a star. On several occasions such passages have been carefully observed by astronomers, and the verdict has been that the star showed little or no diminution of brightness. It is supposed that the nucleus is made up of solid particles, doubtless at some distance apart, involved in a gaseous atmosphere which forms the coma. From these two flows the tail. It seems certain that nothing but gaseous matter constitutes the tail, because the volume.is so immense that by the presence of sufficient solid particles to make the tail visible by reflected light the mass could bo detected. Spectroscopic studies prove that comets shine both by inherent light and reflected sunlight. The true cause of this inherent light is still conjectural. •It is impossible to explain how the tail, which is infinitely more tenuous than our best terrestrial vacuum, can shine so biightlvIu the case of periodic comets of short periods, which are almost continually being subjected to great loss of matter in their tails at successive returns, this appendage must inevitably become fainter on successive returns, and so it is that the unexpected comets which rush into our system from outer space, pass near the sun and are seen for the first and last time, provide the most brilliant and extensive tails during the short, time of their apparition. The comets which are members of our 'system are generally faint and insignificant, as they are Hearing the end of their cometary iifo-.