The Bedside Baccalaureate by David Rubel

Author:David Rubel
Language: eng
Format: epub
ISBN: 9781402772535
Publisher: Sterling
Published: 2016-12-21T00:00:00+00:00

This diagram shows the winter solstice in the Northern Hemisphere.

The earth’s distance from the sun, of course, doesn’t cause the seasons—or else the entire planet would experience summer in January and winter in July. Instead, the seasons derive from the earth’s 23.5° tilt. During the summer months in the Northern Hemisphere, the earth is oriented so that the North Pole points toward the sun. Because of this orientation, only at points north of the equator do the sun’s rays strike the earth’s surface at angles approaching perpendicularity. This is important, because when the sun’s rays strike the earth’s surface at lower angles, their energy in diffused.

Imagine holding a flashlight perpendicular to the ground. The circle illuminated by its beam is bright. Now imagine tilting the flashlight a little. The illuminated oval isn’t nearly as bright, because the same amount of energy is now lighting (or heating) a larger area. The sun’s rays behave in much the same way. The more perpendicular they are, the more energy they convey per unit area.

The winter solstice, the shortest day of the year in the Northern Hemisphere, occurs on December 21 or December 22, depending on the year. On this day, with the North Pole pointing away from the sun, locations north of the Arctic Circle (which begins at latitude 66.5°N) experience twenty-four hours of darkness. Meanwhile, the sun’s rays are perpendicular to the earth at 23.5°S, a line of latitude known as the Tropic of Capricorn. The summer solstice, the longest day of the year in the Northern Hemisphere, occurs on June 21 or June 22. On this day, the North Pole points toward the sun, so the sun’s rays are perpendicular to the earth at latitude 23.5°N (the Tropic of Cancer) and darkness covers locations south of the Antarctic Circle (which begins at latitude 66.5°S).

Equidistant between the solstices are the vernal (spring) and autumnal (fall) equinoxes. On these days, the sun’s rays are perpendicular at the equator, and all locations on the earth experience twelve hours of both daylight and darkness.

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