What Is the Difference Between a Solstice and an Eclipse?

Solstice Basics

• The earth is titled on its axis by approximately 23.4 degrees. This means that as the earth orbits the sun, the poles will be at different distances and angles to the sun. The result is that the sun appears to move across the sky in a north-south position during the course of the year. The solstices mark the point at which the sun is at its northern and southern most position along this track, representing a pause in its relative motion before it reverses its course. The word comes from the Latin words sol and stitium, literally meaning sun stoppage.

Eclipse Basics

• Eclipses represent the alignment of the earth, sun and moon. In the case of a lunar eclipse, the earth is positioned between the sun and moon. This results in the moon passing through the earth's shadow. In the case of a solar eclipse, the moon is positioned between the sun and earth. This results in the moon's shadow passing across the surface of the earth. Those within its shadow will observe the moon block-out the sun. The amount of the moon that passes through the earth's shadow or the amount of the sun that is blocked-out determines if it is a partial or total eclipse.

Difference in Frequency

• Solstices occur twice every year, once in June and once in December. June represents the summer solstice in the Northern Hemisphere and the winter solstice in the Southern Hemisphere, while the December solstice represents the opposite. The frequency of eclipses depends on the orbital position of the moon and the earth. Because the lunar orbit is not in the same plane as the earth's orbit and the distance of the moon from the sun varies with the earth's orbital position, an eclipse does not occur twice every month. Rather, a lunar eclipse only takes place an average of 1.5 times per year, but can range from zero to three. A solar eclipse takes place an average of 2.4 times per year, but can range from two to five.

Difference in Visibility

• Because the solstice represent the shortest or longest day of the year, they are always observable by all. Lunar eclipses, when they occur, are visible to all observers on the nighttime side of the planet, meaning the side away from the sun. Solar eclipses are the most limited in terms of visibility. They are only visible to those observers who are located in a position that falls within the shadow cast by the moon, called the path of totality. This path only covers around 1 percent of the earth's surface, measuring approximately 100 miles in width.