Bill Nemeth, age 10, of San Fernando, Calif., for his question:
Is the sun ever 90 degrees overhead?
The sun climbs its highest on June 21 or 22, the longest day of the year. The official midsummer's day dawns on June 24, after weeks of changeable springtime weather, warm today cool tomorrow. It seems odd that the hottest weeks of the sunny season come later, when the days are shrinking and the noon sun drops lower and 1over in the sky.
Above the city of Los Angeles, the noonday sun on the day of the summer solstice climbs almost $0 degrees up the heavens. In measuring the scope of the sky, astronomers and navigators regard it as the inside of a stupendous ball. It is called the celestial sphere and from our spot on the earth we can see only half of it at a time. This half, like a dome, rests its round rim at the horizon at sea 1evel and its top is the zenith, direct1y overhead.
The geography of the celestial sphere is spanned with circles of longitude and latitude that correspond to the lines of longitude upon the face of the globe. And since ancient times the circle has been subdivided into 360 equal. Degrees. An arch over the visible sky, from horizon to zenith to the opposite horizon is a half circle of 180 degrees. The zenith at mid point on the arch is 90 degrees, or exactly above the observer's head.
Seen from almost every spot on earth, the sun climbs higher or lower with every day of the year. At the equator, where its average height is highest, it reaches 90 degrees at noon on two days of the year. One day is the spring equinox of March 20 or 21 when it crosses the equator on the path that brings simmer to the northern hemisphere. The other is Sept. 23, the fall. Equinox when the sun crosses the equator
On its path to bring summer to the southern hemisphere. From late March to late June, the sun's path creeps north to the tropic of cancer, about 232 degrees north of the equator. Each day the noonday sun is 90 degrees overhead a little farther north. On June 21 or 22 it is directly overhead at the tropic of cancer all around the globe. Then the sun's path moves back to the equator and farther south to the Tropic of Capricorn, on about latitude 232 degrees south. On Dec. 22 the noon sun reaches 90 degrees at the Tropic of Capricorn.
The sun reaches the zenith only within the tropics north and south of the equator. The Hawaiian Islands lie just south of the tropic of cancer. This is the only part of the United States of America where the noon sun climbs 90 degrees overhead. This happens on the few days before and after the summer solstice of June 22.