DAYLIGHT SAVING TIME ENDS
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EARTH AT FARTHEST POINT FROM THE SUN
(June 11, 2008 ) – Astronomers at the Pisgah Astronomical Research Institute announce that at 4 a.m. EDT on Friday, July 4, the Earth, in its annual orbit around the Sun will be at it farthest point from the Sun. Astronomers call this point aphelion.
The average distance of the Earth from the Sun is about 92,918,000 miles. However, the Earth’s orbital path around our central star is not a perfect circle but rather slightly elliptical in shape. Because of this the Earth is slightly closer to the Sun in January, at perihelion, and a bit farther away in July, aphelion. At 4 a.m. on the 4th the Earth will be 94,513,128 miles from the Sun or about 1½ million miles farther than average. This is the farthest away it is for the decade and second farthest for the century*.
Some people find this a bit confusing: The Earth is farther from the Sun in the summer and closer in the winter? Shouldn’t it be the other way around? No! Realize that the seasons have nothing to do with the distance of the Earth from the Sun. The seasons are caused by the 23.5 degree tilt of the Earth’s axis of rotation. In the spring and summer we in the Northern Hemisphere are tilted towards the Sun while in the fall and winter we tilt away from it. The small difference in our distance from the Sun has a very insignificant effect on our seasons and weather.
One effect that does result from our distance from the Sun is the speed of the Earth in its orbit. Near aphelion, when the Earth is farthest from the Sun, it slows down a bit. Vice versa, the Earth speeds up near perihelion. The effect of this is to produce a difference between the actual position of the Sun in the sky and where it would be if its orbit were a perfect circle and it had a constant speed around the Sun. We call this difference the equation of time and it manifests itself in the corrections we have to apply to readings of the shadow on a sundial. It also shows up in the analemma, that funny looking distorted figure-8 we see on some Earth globes.
*Sky and Telescope, Vol. 116, No. 1, July 2008, p. 58.
About PARI
PARI is a not-for-profit foundation established in 1998. Located in the Pisgah Forest southwest of Asheville, NC, PARI offers educational programs at all levels, from K-12 through post-graduate research. The institute is affiliated with the 16-campus University of North Carolina system through PARSEC, a UNC Center hosted at PARI, and is a member of the NC Grassroots Museum Collaborative. For more information about PARI and its programs, visit www.pari.edu.
Some people find this a bit confusing: The Earth is farther from the Sun in the summer and closer in the winter? Shouldn’t it be the other way around? No! Realize that the seasons have nothing to do with the distance of the Earth from the Sun. The seasons are caused by the 23.5 degree tilt of the Earth’s axis of rotation. In the spring and summer we in the Northern Hemisphere are tilted towards the Sun while in the fall and winter we tilt away from it. The small difference in our distance from the Sun has a very insignificant effect on our seasons and weather.
One effect that does result from our distance from the Sun is the speed of the Earth in its orbit. Near aphelion, when the Earth is farthest from the Sun, it slows down a bit. Vice versa, the Earth speeds up near perihelion. The effect of this is to produce a difference between the actual position of the Sun in the sky and where it would be if its orbit were a perfect circle and it had a constant speed around the Sun. We call this difference the equation of time and it manifests itself in the corrections we have to apply to readings of the shadow on a sundial. It also shows up in the analemma, that funny looking distorted figure-8 we see on some Earth globes.
*Sky and Telescope, Vol. 116, No. 1, July 2008, p. 58.
About PARI
PARI is a not-for-profit foundation established in 1998. Located in the Pisgah Forest southwest of Asheville, NC, PARI offers educational programs at all levels, from K-12 through post-graduate research. The institute is affiliated with the 16-campus University of North Carolina system through PARSEC, a UNC Center hosted at PARI, and is a member of the NC Grassroots Museum Collaborative. For more information about PARI and its programs, visit www.pari.edu.