Earth at Aphelion: Norwood astronomer says Sun not as close as you might think
Wednesday, June 30, 2010 - 6:00 am

By BRUCE McCLURE

With the hot days of summer now upon us, you might think we're about as close as we can get to the Sun. Actually, nothing could be further from the truth. On July 6, 2010, the Earth reaches its most distant point from the Sun for the year -- a point astronomers call "aphelion."

On the average, our planet resides about 93 million miles from the Sun. But since the Earth doesn't orbit the Sun in a perfect circle, its distance from the Sun varies throughout the year. Sometimes, we're as close as 91.5 million miles; at other times, we're as far away as 94.5 million.

Keep in mind, however, that it's not the Earth's distance from the Sun that determines the seasons, but the tilt of the Earth's axis. In summer, we tilt toward the Sun and in winter we tilt away.

Although aphelion comes when it's summer in our Northern Hemisphere, it doesn't always coincide with the hot season over the long course of time. One thousand years ago, aphelion occurred at autumn, but five thousand years into the future, it'll take place in spring.

Earth's varying distance from the Sun -- though not responsible for the seasons -- does affect seasonal length. At aphelion the Earth travels most slowly in its orbit, causing the season in which it resides to elongate. At the present time, that makes summer the longest season in our North Hemisphere, and winter the longest season in the Hemisphere "Down Under."

-- Bruce McClure of Norwood is a freelance astronomer and a frequent contributor to "StarDate" and "Earth and Sky" radio programs. His web site is idialstars.com. He and his wife, Alice McClure, present hand-on learning opportunities and workshops.