Equinoxes good for finding due east, west, little else

The Big Dipper is climbing higher in the northeast sky while the mighty winter constellation Orion and his familiar cohorts begin their western plunge. Once again we enter a phase where we are looking out of the plane of our galaxy and so have lesser stars and constellations to look at for a while. But since sunset occurs later and later, it seems the next cycle of stars spring up from the eastern horizon faster and faster. Leo the lion, in particular, appears to lunge westward.

The primary astronomical event in March is the vernal equinox, which occurs on March 20. Because the Earth's axis of rotation is tipped 23.5 degrees from its orbital plane we see the sun glide above and below the equator through the course of a year. When the sun appears to be right above the equator we call this the equinox, which means "equal night." No matter where you live on the Earth, you will have 12 hours of daylight and 12 hours of night, even if you are on the North Pole!

When the sun is at its maximum above and below the equator we call that the solstice, which means "stands still." The sun's apparent path among the stars appears to stand still as it reaches its peak deviation and changes direction.

The equinoxes represent spring and fall, while the solstices signal summer and winter.

For some reason, people try to make special significance out of the equinoxes. I was once asked if I could balance an egg on its end during the equinoxes. Even today we sift through nature's offerings looking for significance to help us make it through life. The only thing science holds the equinoxes special for is finding due east and west. On these dates the sun will rise exactly east and set exactly west. This makes it a good time to align your sundial or your pyramid.

The planets Jupiter and Saturn remain nearly overhead at sunset. They will continue to give us good views for another month or two before they join the next great planet alignment in the west come May.

From time to time the various planets appear to align close together in the sky from Earth's perspective. Once again many people are eager to ascribe special significance to the event. The most popular prediction is that the gravity from the planets will all tug at the Earth from the same direction at the same time and cause earthquakes.

From the Earth's point of view, the two most gravitationally important bodies in the universe are the moon and the sun. The moon by far has the strongest influence on the Earth, causing our daily tides. Despite the sun's enormous mass, its tides are only about one-third as strong as the moon's because it is so far away. During the full and new moon phases, the tides from the moon and sun enhance each other and give us supertides.

So balance your eggs if you can, hang on for the ride and this time when you do ride into the sunset, it will be in the west.

Dr. Michael Cobb is a physics professor at Southeast Missouri State University.