SOLAR DISTANCES

Hokitika Guardian, 31 July 1930, Page 2

SOLAR DISTANCES

WELLINGTON OBSERVATIONS

EYES ON LITTLE EROS

Concentrating its attention mainly on the small planetary body called Eros, one of the tinier members of the solar’ system, the 9-inch Cooke telescope at Kelburn Observatory will in the near near future be lending its aid in a campaign designed to furnish an accurate scale of distance for our maps of the solar system. Its observations, combined with those, of certain other observatories, are to be undertaken at the instigation of Solar Parallax Committee of International Astronomical Union, which is anxious for the work to be done in order that the astronomical unit of distance—the mean distance of the earth from the sun—may be vertified and perhaps corrected. This is .the second “Eros campaign" to be held under similar circumstances, the Inst having been held in 1900-01.

ASTEROID FAMILY,

Eros is one of the minor plants oi asteroids of which a large number are known, and to whose number fresh members are being added constantly. Their paths round the sun lie for the most part between the paths of Mars and Jupiter. Eros, however, which was discovered in 1898, spends some of ■ its time within the region named, but spends the remainder running along between the orbits of Mars and the earth. At one time it lies only a mere step away from the path of the earth, mstromonomically speaking. Only 14 million miles separate the two orbits. To make most use of this circumstance it is necessary for the earth and Eros to be actually in this part of their orbits, close to each other at the same time. Although this may sound obscure, it is less obscure than speaking of the most favourable opposition, which the conditions imply. The last time this; fortunate combination of circumstances arose was iif 1900-01, and similar ones follow at intervals of 30 years. V ’

The whole, idea is to get some outside member of the sol.ar system close enough to work what surveyors call triangulatioh. A distance on the earth can be taken as a base line, and the directions of the body at each end of the line can be taken determined. From these data by calculations, the distance of the body can be prepared, but without a knowledge of any actual distance between bodies in the system, the map can only remain as a proportional representation of planetary affairs. Let one actual distance be determined, however, and it pulls the whole map on a definite scale of distances.. This is what is sought with Erps. When its distance has been worked out any other distnnoe in the solar system, including that of the earth frpm the sun, are obtainable. Like Almost everything else ip the sciehoe mw, the observations will he made photographically,

NEARING ACCURACY,

In the 1900 Eros campaign, 18 telesopes were engaged in making observa';ons. The problem before them was to attempt to measure the quantities with such accuracy that the final calculated distance of the sun would be correct to at least one part in a thousand, Mr A. R. Hinks, of Cambridge Observatory, was responsible for the co-ordina-tion of all the Eros observations ,and after years of work the final result was that the distance between the earth and the sun was 92.9 million miles. Related to it was the solar parallax, or angle subtended at the sun by the earth’s radius, Thus quantity was calculated to be 8.80? seconds of arc,

The Kelburn Observatory will co-op-erate with observatories at Corboda and La Plata, where instruments of the same focal length will be used. The results of the throe observatories will therefore be comparable.