SUMMER SOLSTICE

Otago Daily Times, Issue 23689, 22 December 1938, Page 7

SUMMER SOLSTICE

LONGEST DAYS OF THE YEAR It happens that both to-day and to-morrow of this week have the distinction of being the longest days of the year. Mr W. D. Anderson, of the Astronomical Branch of the Royal Society, states that we are now approaching that part of the year when the sun attains its most southerly point, bringing with it the longest days in this hemisphere. This point will be reached at midnight on the 22nd, when the sun enters the zodiacal sign Capricornus. The sun at this time is approximately 91,000,000 miles distant, and will then occupy a position about 1600 miles south of the equator. If the earth rotated on an axis perpendicular to its plane of revolution, climate, as regards heat received from the sun, would be mainly a matter of latitude, and in each latitude there would be a constant quantum of heat received every day. But the matter is not so simple as that. The axis of the earth's rotation, as we know, is inclined to the plane of its orbit of revolution to the extent of about 23Jdeg. The result of this inclination is that the sun gradually in the course of the year moves northward across the equator to latitude 23deg 68min north, and then appears to turn and move southward across the equator to latitude 23deg 68m,in south. The effect of this movement is obviously to vary the height of the sun above the horizon from day to day in both hemispheres. From December 23, the so-called summer solstice, to June 22, the so-called winter solstice, the sun moves northward and day by day makes a larger and larger arch in the sky in all places in the northern hemisphere, and a lower arch in the sky in all places in the southern hemisphere. From June 22 to December 23, the sun moves southward and the reverse movement takes place, the sun moving southward and making an increasingly higher arch in the sky in this hemisphere. Thus we have our seasons and the climate is accordingly not merely a matter of the latitude of the place but a matter of the varying latitude from day to day of the sun itself. In short, the varying heat of the varying seasons of the earth is not due merely to the sun's varying distance from the earth, but the height the sun attains above the horizon of any place at any time so that in' winter we have short days, long nights and oblique sun rays, and in the summer long days, short nights, and more perpendicular sun rays. The mainspring of the climate is the mutual relationship between earth and sun. Thus the orbit of the earth, the rotation of the earth, the inclination of the axis of the earth in relation to the sun govern the climates of this planet.