IN STARRY SKIES

Evening Post, Volume CXI, Issue 67, 20 March 1931, Page 13

IN STARRY SKIES

THE HEAVENS THROUGH FIELD GLASSES THE LUNAR SURFACE

(By "Cnuc Austrnlis."

Tbo moon provides in a telescope tho grandest scenery available in tho wholo of tho solar system. The absence of an atmosphere and tho bold relief afforded by contrasts of light and shade enablo us to see under a good magnification a great variety of the rugged scenery of our satellite. In describing in this column last week ■what could bo seen of tho moon through field glasses it was possible in the space availablo to give only an outline of the various lunar features. Seen through a telescope tho predominant feature of tho lunar surface- is the circle. Some of the "seas," tho dark, smooth areas, are practically circular, surrounded by ranges of mountains. Next to tho seas in point of size are the walled plains. Circular, flat expanses surrounded by steeply rising walls, very similar to the craters in appearance- but of great size, these features can be scon in overy stage of development or decay. While in some cases the rings •urrounding these immense plains are

perfectly preserved, in other places rings can bo seen which have been almost obliterated by the surrounding detail. Broken clown walls, largo craters overlapping, and small craters pitted both inside and out of the plains and also on tho walls themselves, are common details of the3O wonderful ■structures, so Large, indeed, that a person standing at tho centre of the plain would bo unable to see the surrounding walls, which in many cases aro so farspread as to be below the horizon as seen from tho centre. Noxt in size arc the craters, of a wide? variety in sizes, but all exhibiting the common circularity of the other features. The illustration accompanying this article is a photograph of a group of craters lying near the moon's centre. This photograph was taken early in the present century at the Yerkes Observatory in tho United States by G. W. Hitch ey, who is responsible for many beautiful photographs of the heavens. The photograph was secured with a. forty-inch refractor, an idea of its groat size being gained by comparing jt with the handsome nine-inch refractor housed in the Wellington Municipal Observatory, which itself is ono of the largest telescopes in New Zealand. The area covered by the photograph is roughly 320 miles by 240 miles. South is at the top of the photograph, as tho moon is seen in this hemisphere by the naked eye. Tho large -walled-plain near tho centre is named Theophilua. This

plain is Cl miles across. The crater wall rises to ;i height; of 19,000 feet. above tho plain, and tho cent nil peak, an object possessed by almost all 1-h»: ■ craters and walled plains, rises 10,000 foot abovo the plain. It cau be clearly seen in the illustration that Thcopliflus is of more recent origin than tho crater lying south-east of it, Cyrillus. This is evident because the moro recently formed w;ills of Thoophilusi intrude on the older walls of Cyrillus. There are a number of other craters in the photograph. Sixty-live miles south of Cyrillus is Catliarinii. All around are smaller craters, and over all aro scattered minute pits termed craterlots. Tho dark area filling the southwestern corner or' the photograph is portion of tho Maro Nectaris, or the sea of nectar. An excellent illustration of the number of craters on the moon is gamed from the knowledge that over 30,000 craters have been mapped. As flu: moon always turns tlio same face towards us, we cannot say what lies on tho remote side, but as it is almost certain that the lunar surface is similar on both sides there must bo over 60,000 craters on the whole surface. Tho lunar craters aro distributed indiscriminately over the moon and range in size from tho tiniest of pits visible only under high magnification to immense walled plains up to 150 miles in diameter. It is remarkable that in all the years astronomers have been able to study these markings throgh telescopes the origin of the water-like markings seen has not yet been determined. Owing principally to their circular-

ity and similarity to terrestrial volcanoes the theory of their origin which was first widely believed in was that] these lunar rings were volcanoes, similar to those we have on the earth. It was believed that at sorao past time the moon was volcanically very active, and that the crater pits have remained as evidence of the groat eruptive powers once present on our satellite. The volcanic theory in recent years has fallen into disrepute. There are so many craters, of such great size and so indiscriminately scattered, that their volcanic formation docs not seem likely. Scientists nowadays incline to the belief that the moon's face is pitted with the scars of a tremendous meteoric bombardment. In the neighbourhood of tho earth space is well filled with meteoric material, which often eneountorß the earth, producing the familiar spectacle of a falling star. There are seevral large craters on the earth's surface undoubtedly produced by falls o£ meteoric masses. Notable among these is Meteor Crater in Arizona, a pit nearly a mile across dug out of tho de-sort by the fall of a large mctoric mass. In Siberia thero is another instance of a meteoric fall in which small cratcrlets are spread over a large area. It is argued tlwt tho moon, without a protective atmosphere to absorb most of these bodies, has been subjected in the course of centuries to a great bombardment, the sears from which remain the subject of speculation to the present day.