OF CURRENT INTEREST

Taranaki Daily News, 1 June 1935, Page 13 (Supplement)

OF CURRENT INTEREST

THE SOUTHERN CROSS

(By the

Rev. B. Dudley, F.R.A.S.)

Facing south at 8 pm. during the present month, the Southern Cross will be found almost upright and high overhead ; with the Coal Sack lying as if in a heap at its base on the eastern side. The lowermost star of the four, or Alpha Crucis, is the brightest. It is also an interesting triplet. The telescopy reveals two glorious suns very close together. These, it has been found, revolve about each other in a long period of time (at present unknown); while the third member of the trio ’ is h very much fainter object though easily picked up in a small telescope. The duplicity of the main star requires, to be detected, an instrument of about two inches diameter. Gamma, the star at the top of the Cross, is also a double, a very wide telescopic object. Close to Beta, the second brightest in the constellation, is one of the reddest stars in the sky. Kappa has special interest in that it is surrounded by a beautiful cluster of suns of various colours, the famous “Jewel Casket of Sir John Herschel. The Coal Sack contains only one star visible to the naked eye. Photography has, however, revealed the existence within it of quite a large number. The Pointers will be readily-recognised on the east of Crux and directed to a place near the head of;the constellation. The brighter of the two—the more distant from the Cross—really belongs to the Centaur, the brightest in that constellation, and .is known therefore as Alpha Centauri. It is the finest double star in the entire heavens. A smalltelescope “splits” it. The component stars make a revolution about their common centre every 77 years. Although the space between them is so small that a telescope is required to detect it, that space is in reality 1,875 million miles across. The distance of this double star from us is 26 million million miles. The light of Alpha Centauri takes 4J years to reach us. This is the nearest bright star to'the solar system. ' Achemar is seen corruscating low on the meridian, the imaginary line drawn from the zenith down to the southern horizon. The upright beam of the Cross points almost directly towards it- while about half way between the Cross and Achemar is the south pole of the heavens. This alignment is an excellent method of finding the celestial Pole.

Mercury the Elusive.

The planet Mercury'is now in our evening skies, but is fast approaching the sun. On the 21st fit is in inferior conjunction, thereafter becoming a momipg star. Recent conversation with some keen students of the sky, observers who have not been slack in their efforts to glimpse it, helps to explain the admission made by Copernicus that although he had greatly desired to see this planet, he had never once beheld it. It would be difficult to understand, however, that a watcher of the skies resident on the plains or where the horizons are not'obscured by hills or other obstructions could miss it altogether, as did Copernicus. The writer, who" has-4iever gone out of his way to see Mercury, has -to confess that only on a Very few oc-. casidns has he detected it; and’ one. of these’was when the planet was making a transit across the sun’s disc. Merciuy may well be described as “the elusive world.” Towards the latter end of the nineteenth century, the Italian astronomer -Giovanni Schiaparilli, who also dijd remarkable work in the observation and study of Mars, startled the scientific circles by announcing that Mercury was not subject to a rotational motion like that of the Earth which, spins . upon its axis. This tiny world, he affirmed, keeps always the same face to the .solar orb. Therefore it turns .once round upon its axis while revolving once; , roUrid the sun, very much afc the moon keeps ever the same face to the earth, revolving upon her axis in precisely the same time as it takes her to journey once round her primary. After the closest possible, scrutiny, extended over a long period, he found that certain definite markings on Mercury’s disc were always to be seen in the same place. Subsequent observations with improved instruments have established the correctness, of findings. This interesting little, world cannot boast of a dense atmosphere. As a matter of fact, it has an almost inappreciable quantity of “air.” Dr. F. R. Moulton and others think that it is probable that its surface is very rough and comparable in a general, way to that of the moon. It apparently has not been subject to the weathering and smoothing action of air and water. “Yet in the long run,” writes the doctor, “the small meteors which probably fall upon the planet in countless millions may have gradually beaten its. surface smooth, though an occasional very large one would make it perhaps as rugged as the face of the moon.” ’ Modern astronomy has been obliged to take’ more account of the cosmic effect?: of meteoritic action than lnterplanetary space is not devoid of -matter by any ineans. The sun and nearby planets are constantly bombarded with meteors. Fortunately for ourselves, the earth ,is protected by its dense atmospheric covering which by friction fuses nearly all these bodies into vapour or dust. In the remote past such impacts must have operated on a much larger scale than now. It is likely that the irregularities on the lunar surface are one , result. Having no air and therefore no water and .other disintegrating influences in action, these irregularities have not been worn down, as they have in the case of our own planet.

Partial Eclipse on June 30. On June 30 a partial eclipse of the sun takes place, being visible in north polar regions, parts of Siberia, northern Russia, Finland, Norway, Sweden, Greenland, and Iceland. A trace of it will be seen from the British Isles at about sunset. According to local time the event takes place on July 1. The j ear 1935 is a year of five solar eclipses, and two lunar. That of the sun on January 5, however, was a very small one. Since the introduction of the Gregorian calendar the following years only have had seven: 1591, 1656, 1787, 1805, and 1917; future seven-year eclipses after 1935, are 1982 . and 2094. It will be seen, therefore, that in five cen-:. turies, there will be but. eight' years with seven eclipses. The phenomenon of solar eclipses runs through a series known as the sards cycle. The cycle ending with the eclipse of last January (sth) began in the year 528 A.D. (August). Each cycle contains on the average 71 eclipses both of the sun and of the moon.