by Paul Lines

Created on: June 15, 2008

During the course of the earth's 365.26 day orbit around the sun, it passes through two solstices, being the start of summer and winter, and two equinoxes, being spring and fall. To understand the difference between the solstice and equinox, and indeed the effect that each one of the two pairs has upon our planet and lives in terms of creating the seasons that we experience, it is necessary to look at the way that the earth and its orbiting path behave.

Like any other revolving object or planet, the earth revolves around its own axis at the same time as it is orbiting the sun, completing one revolution every twenty four hours, which we call a day. However, the earth's axis is not in a perfect perpendicular position. It is tilted to one side at an angle of approximately 23.5 degrees. Similarly, the orbit of the sun is not a perfect circle, following more of an elliptical path. The tilt of the earth, combined with the orbit path, plays an important part in determining both the seasons on the planet and, equally importantly, the differences that occur in the amount of daylight and night time hours that we experience during the course of a calendar year. The solstices and equinoxes mark significant points in these differences.

Solstice

As stated earlier, there are two solstices. One is known as the summer solstice, which occurs in the northern hemisphere around June 20 to 22. The other takes place between the same dates in December. What happens at the summer solstice in the northern hemisphere is that this part of the earth is tilted towards the sun and, at the same time the sun is at its highest point north and its greatest distance away from the earth. As we all know, a light source will create a greater circle of illumination when it is further away from an object and takes longer to move across that object than if it is close to it. Similarly, at the highest northern point and distance from the earth (the summer solstice), the sunlight is being spread across a wider area of the earth's surface and illuminating that area for a longer period during the earth's rotation. Combined with the tilt, this means the northern hemisphere experiences longer days. However, these will differ from the equator, where the difference between night and day hours varies little, to the North Pole, which at this time of year will experience 24 hour daylight. However, locations between these two points will still experience longer hours of daylight than at other times of the year

Conversely,

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