Close Approach of Mars

Abstract

MARS was in opposition with the sun on July 23, and was nearest the earth, at a distance of 36 million miles and with an angular diameter of 24·1”, on July 28. Despite the closeness of the approach, the apparition is a most unfavourable one for observation in high northern latitudes. This is because of the planet's very large south declination. In May its declination ranged between -22½° and -23°; by the end of June it increased to -24°; and it is now -27°. Thus, since observations began, the altitude above the horizon in the latitude of Greenwich has never exceeded 16° and is now less than 12°. It follows that observers in Great Britain and in most northern observatories cannot expect to get good views of the planet during the present apparition. We shall have to rely almost entirely for our results on observers in the southern hemisphere. Astronomers in northern latitudes may look forward confidently to the next apparition in 1941; for then the planet will be high in their skies and not very much farther away from the earth. During the present apparition, the southern hemisphere of Mars is tilted towards the earth, the latitude of the centre of the disk being -12° at the beginning of June and -7° at the end of August. The spring equinox of Mars’ southern hemisphere occurred on June 1; the summer solstice will occur on October 24.