Jane Ann Heilman, age 10, of Allentown, Penna., for her questions
What is the solstice?
Today is the summer solstice, June 22. The winter solstice, December 22,is the shortest day of the year. The solstices are related to the equinoxes which fall on March'21 and September 23. At the equinoxes, day and night are of equal length all over the world.
The word solstice comes from two older words meaning sun and stand. On the day of the solstice, the sun seems to stand still in its path over the heavens. No., it does hot stop is its daily path over the sky. The sun has another heavenly path which changes with the seasons. It is this path which is marked by the solstices and the equinoxes.
This seasonal path depends upon where the sun is overhead at noon. On March 21, the noon sun is exactly overhead at the equator. A few days later, it is overhead in regions a little north of the equator. In the northern hemisphere, each day now gets a little longer than the one before it. Also, the sun rises a little further southeast each morning and sets a little further to the southwest.
Day by day things improve for those of us who live north of the equator. The noon sun gets higher in the sky and the days get longer. Today, the sun has reached the limit of its northward journey. The noon sun is as high as it will get and this is the longest day of the year. For a few days, the sun seems to stand still in its heavenly path. At noon it is overhead at the Tropic of Cancer north of the equator.
South of the equator things are dust the opposite. Today the people down there are having their shortest day of the year. Their noon sun is the lowest it aver gets in the sky. But this situation soon changes. A few days after our summer solstice, the sun is a little lower in the sky and the days begin to get shorter. South of the equator, things begin to improve. Each day gets longer and each noon sun climbs a little higher in the sky.
In its path over the sky, the noon sun. Is returning to the equator. On September 23, it is exactly overhead. It continues can south of the equator until December 22. On this day the sun is overhead at the Tropic of Capricorn, south of the equator. Our noon sun is as low as it gets and we have our shortest day of the year. After this, the sun stands in its heavenly path and turns north again.
The solstices and the equinoxes occur because the earth's axis is tilted. The axis is an imaginary rod through the center around which the earth spins once each 24 hours. The orbit is its yearly path around the sun. The axis is tilted towards its orbit which causes it to bow first its north pole and then its south pole towards the sun. If the axis were at right angles to the orbit we would have no solstices and no equinoxes. There would be no changing seasons and day and night would always be equal all over the world.