Solstice

From ArticleWorld

The solstice is the point in time when the earth is the most tilted in relation to the sun. There are two solstices, which mark the longest and shortest days of the year, as well as the first days of summer and winter, respectively. The summer and winter solstices are switched on the southern and northern hemispheres. Thus, the winter solstice in Europe will correspond to the summer solstice in South America.

Cause

The solstice occurs because the earth is tilted on its axis. Depending on where the earth is on its circuit around the sun, the angle of light received is either more or less pronounced. When the sunlight hits a hemisphere more directly, temperatures rise, and when the hemisphere is tilted away from the sun, temperatures fall. Every part of the world has seasons corresponding to these warming and cooling trends.

History

In ancient times, it was observed that the sun appeared to move gradually from north to south throughout the year, and then to stop and change direction at the solstices. It is for this reason that solstice festivals were often the most important events of ancient cultures around the world. Today we still consider the first day of summer to fall on the summer solstice and the first day of winter to fall on the winter solstice. There is currently some debate about whether or not the holiday of Christmas was loosely based on the ancient European winter solstice.

Effects by latitude

It is important to note that the tilt of the earth does not change year by year, but that it only ‘’appears’’ to change in relation to the angle of the sun’s radiation as it moves in its yearlong orbit. The two hemispheres of the earth experience nearly equal and opposing effects of axial tilt in relation to the sun’s light.

The north and south axial poles (not to be confused with the magnetic poles) experience the most extreme effects at the solstices. During and around the solstice in June, the sun never rises in Antarctica and never sets at the north pole. In late December this phenomenon is reversed for the two poles.

Each pole has an arctic or Antarctic circle. These are geographically defined areas around the poles where these extreme lighting effects can be seen. At the northern hemisphere summer solstice, the arctic circle defines the area north of which the sun does not set. During the winter solstice, this is the area north of which the sun does not rise.

The earth’s equator, being at the center of the globe, sees very little change in the angle of sunlight received. On both the winter and summer solstices, the day is 12 hours long with 12 hours of night following.

In the earth’s tropical zone, between the Tropic of Capricorn (South) and the Tropic of Cancer (North), the sun’s effects are pronounced throughout the year, but the days can vary by approximately three hours between the summer and winter seasons. These two tropics mark the southernmost and northernmost latitudes where the sun can appear to be directly above the observer on their respective summer solstices.