STARRY HEAVENS

Southland Times, Issue 22293, 7 April 1934, Page 11

STARRY HEAVENS

NOTES FOR APRIL.

(By

R. D. Thompson, M.A., M.Sc., F.R. A. S.)

The Planets. Mercury is at present a morning star, and was at its greatest elongation 28 degrees west of the sun on April 2. It will soon commence to retreat rapidly towards the sun, with which it will be in superior conjunction about the middle of May. The planet Venus, rising about 3 a.m., is also in the morning sky, and shines brilliantly in the east before sunrise. Venus will continue to grace the early morning skies for many months to come The planet will be at its greatest elongation of 46 degrees west of the sun on April 16, and moving thereafter very slowly towards the sun, will not reach conjunction until November, and so will not be prominent again in the evening skies until the early months of next year. Mars is at present too near the sun to be visible, and will actually be in conjunction with the sun on April 14. The planet Jupiter is a brilliant object in the eastern sky during the evening. Rising now about 7 p.m. in a direction a little to the south of east, the planet mounts steadily upwards during the early evening hours, reaching the meridian soon after midnight. Jupiter will be in opposition to the sun on April 8, when the sun, earth and planet will be practically in one straight line. Saturn is at present very close to Venus in the early morning sky. and the two planets now rise almost simultaneously, Saturn being a little to the south. Their distance of separation, however, will rapidly increase,, and Saturn will appear above and well to the south of Venus by the end of the

5 month. Some Prominent Constellations. > The evening sky is at this period of , the year rich in well-known bright . stars and constellations. Between 7 and : 8 p.m. on the present date the familiar > group of Orion, the Hunter, appears > high in the north-western sky, with the • bright-reddish star Betelgeuse to the • north and the brilliant white star Rigel ■ to the south. Betelgeuse is a “giant” ; star with a diameter of some 200,000,- , 000 miles. Still farther to the north- ■ west and much lower in the sky, is i Aldebaran in the constellation of Tau- ■ rus, the Bull. High up, apparently al- . most overhead, but slightly to the : north-west, is Sirius, the Dog Star, the brightest fixed star in the whole sky, while farther to the north, and somewhat to the east of Sirius, is Procyon of the Little Dog. Still farther north, and much lower in the sky are the Twins, Castor and Pollux, Castor being the lower’ star, while Pollux, now the brighter, is higher and a little to the right. Castor is a “double” star, and can actually be seen as two separate stars in a telescope of only moderate power. These two stars revolve around one another in a period of over 300 years. A third star forming part of the same system has also been discovered in later years, while still more recently all three stars of the system have been proved to be themselves double stars. Thus the apparently single star Castor is really a group of six stars. To the north east and fairly high in the sky is the star Regulus in the Lion, and the plant Jupiter, almost due east, may readily be distinguished by its brilliant steady glow. The bright star a little higher and to the right of Jupiter is Spica in the constellation of the Virgin. The Southern Cross is to the south-east, the two “pointers,” Alpha and Beta Centauri being in a line to the south. High overhead, but a little to the south-west is Canopus, second only to Cirius in brightness, but whereas Sirius is only a little over eight light years distant, Canopus, which is only a little less brilliant, is known to be enormously remote, and so must be incomparably brighter in itself.

Path of the Moon. The moon in its passage across the sky during the month may serve as a pointer to indicate some of the brighter stars and constellations. In the early morning hours of April 10 the moon will be very close to the planets Venus and Saturn, and will pass the planet Mercury on the 12th. New Moon occurs at mid-day on the 14th, and the planet Mars will be passed some four hours later. By April 17 the moon will be to the north of the star Aldebaran, and on the 18th well to the north of Orion. Castor and Pollux will be to the north of the moon on the evening of the 20th, and on the 24th the moon will pass very close to and just to the south of Regulus. By the evening of the 18th the moon will be near the planet Jupiter, and will pass very close to the bright star Spica at midnight on that date. Full Moon occurs at midnight on April 29-30.

The Scale of Space. The question might well be asked as to how the astronomer determines numerical values for the enormous distances with which he is concerned. One speaks glibly of the sun’s distance from the earth as being 93 million miles, or of stellar distances ranging from four or five light years up to 100 million light years, but the problem of actually measuring these distances might well appear insuperable. No measuring guage can be directly applied, and yet the distance of the sun from the earth—the fundamental unit of distance in astronomy—is now known to within an accuracy of one-tenth of one per cent. “The sun’s distance,” writes Mr Peter Doig, “is the fundamental datum of astronomy—the unit of space, any error in the estimation of which is multiplied and repeated in many’ different ways, both in the dimensions of the solar system and in those of the universe in general. The number which represents it is involved in almost every calculation of distance or masses, of sizes and densities either of planets or their satellites, or of the stars. Its determination has been referred to as one of the noblest problems of the science, and great expenditure of human effort and wealth has been made in attempts at its solution. It is also among the most difficult tasks of the astronomer, involving as it does, in the direct methods, an attempt to measure an angle about equal to that subtended by a halfpenny 2000 feet from the eye, within about a thousandth part of its value.”

Different methods of varying degrees of accuracy have from time to time been employed to solve this promlem of ascertaining the distance between the sun and the earth, and hence of determining the dimensions of the solar system, and ultimately of the visible universe. Many of the methods of finding astronomical distances are necessarily somewhat mathematical in character, but it is hoped to give in this column in the near future some popular idea of the ways in which the astronomer has attacked the problem.