On Sept. 22 all things dark, light will be equal


POSTED: Tuesday, September 01, 2009

For one day this month, equality will reign. On Sept. 22 every place on Earth will receive equal amounts of day and night. Unless you are sitting on the equator, this only happens on two days of the year: the September and March equinoxes. The word “;equinox”; comes from the Latin words meaning “;equal night,”; short for “;daylight equals nighttime.”; Many cultures around the world have celebrated the equinox as a marker of the change of seasons.

To understand what the equinox really is, imagine drawing a line from the North Pole to the South Pole. This is Earth's axis, around which Earth rotates once every 24 hours, causing day and night. But Earth's axis is not straight up and down; it is tilted. As Earth orbits the sun, the position of Earth's axis changes relative to the sun. When Earth's axis is leaning toward the sun, it is summer in the Northern Hemisphere, a time of longer hours of daylight and more direct rays from the sun. When Earth's axis is leaning away from the sun, it is winter in the Northern Hemisphere. The opposite is true of the Southern Hemisphere.

At the equinoxes, Earth's axis is leaning neither toward nor away from the sun. This means that both the Northern and the Southern hemispheres are receiving the same amount of sunlight. Keep in mind that Earth is constantly moving in its orbit around the sun. This means that the true equinox is not a whole day, but only one moment in time. In 2009 the autumnal equinox in Hawaii takes place at 11:18 a.m. Sept. 22.


This month's spotlight actually includes three different constellations that make up the summer triangle: Cygnus, Lyra and Aquila. Despite its name, the Summer Triangle continues to be visible high in the evening sky throughout September. Look for three bright stars that make up the triangle. The star Altair in the constellation Aquila gives us the southernmost point in the triangle. The star Deneb can be found in the constellation Cygnus. The third star, Vega, is part of Lyra.

The Summer Triangle can be seen even in the midst of bright lights of Honolulu. In fact, sometimes it can be even easier to identify the triangle shape when the fainter stars are washed out. But if you are lucky enough to be stargazing in a very dark place, you might see the Milky Way flowing through the center of the triangle.



Jupiter continues to dominate the night, visible in the southeast after sunset then moving toward the southwest as the night progresses. Look for the near-full moon close to Jupiter tonight and tomorrow.