DISCOVERIES AMONG THE SOUTHERN STARS.

Otago Witness, Issue 3590, 2 January 1923, Page 59

DISCOVERIES AMONG THE SOUTHERN STARS.

Studying photographic plates made in Peru at the Arequipa station of the Harvard College Observatory, Harvard astronomers liave discovered during the summer more than 2000 nebula;, several new variable stars, and one nova or new star, and have now measured for the first time the distance and size of the Large Magellanic Cloud, a cloudlike group of stars and nebulce visible from the southern hemisphere, and resembling in experience the Milky Way, says a dispatch from Cambridge, Mass., to the New York Times: “This Magellanic Cloud, which is believed to be a sort of small universe in itself, separate from the Milky Way system of stars of which our own solar system is a comparatively- infinitesimal part, proves to be of staggering dimensions. Its distance from the earth, while not the greatest distance ever measured by astronomers, is eo immense as to be almost beyond human powers of comprehension, being 110,000 light years. A light year is six trillion miles, the distance travelled in a year’s time by light, which covers 186,000 miles in a single second. “Tlie linear diameter of the cloud has been found to be about 15,000 light years. This is determined by finding the distance which observers work out by complicated methods involving spectroscopic studies, and then measuring the apparent size of the cloud as it appears on photographic plates made at Arequipa. “Photometric measures of the stars in tlie large Magellanic Cloud make it possible, now that their distance is known, to find their actual candle-power. This work is still in progress at Harvard, but preliminary results would seem to show that this cloud contains many- stars which are actually far brighter than any we have yet discovered in our stellar system, although, of course, they appear very faint on account of their immense distance. Hundreds of these stars are found to exceed the brightness of the sun by 10,000 times. “Photometric investigations are being continued at Cambridge in order to get a more precise measure of the -distance of the cloud by other methods than the spectroscopic method provisionally- used,and to set up standards of brightness in the cloud so as to make possible the study of various types of stars and nebulae existing there." ' The methods followed ( in finding the 2000 nebulae are characteristic of modem astronomy, the writer tells us. They were found bv the study and comparison of photographic plates made at Arequipa during the last 20 years. The total number of known nebulae is about 20,000, and more than one-fourth of these have been found at various times on plates made with a single telescope, the Bruce photographic refractor, one of the most powerful photographic instruments in the world, and one of four instruments in constant use at the Harvard station at Arequipa. To quote further:

“The 2000 newly-discovered nebulas are mostly too far south for observation at the observatories of North America, but many.of them are relatively conspicuous and important. “Of the new variable stars discovered during the summer on plates made at Arequipa, some were found by- the observers in South America and some by tTif> workers at Harvard on old plates. One of the variables, discovered by Professor S. I. Bailey, is extremely faint, like the vari« ables in the globular clusters, but nearly a degree away- from the nearest cluster, which suggests that these variable stars are escaping from the clusters. “Tlie Arequipa station is situated in Peru, at an altitude of 8000 ft. The work there is in charge of Prcfrssor S. I. Bailey, who played a prominent part in the establishment of the station over 30 years ago, and served as acting-director of the observatory in Cambridge during the interval between the death of Professor E. O. Pickering in 1919 and the appointment last year of Professor Harlow Shapley as his successor. _ “Professor Bailey has recently taken a large number of photographs at Arequipa for the study of the motions of the stars, and the variations in their light. He has made several exposures extending over two nights with the Bruce telescope. Single photographs taken with this powerful instrument frequently show more than 500.000 stars. In the clouds of stars in the constellation Sagittarius, recent Harvard plates show the individual stars to be so extraordinarily numerous that the moon could hide 10,000 of them at a time.”