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July 06

orbits of the four closest planets and of near-Earth and potentially hazardous asteroids Image Credit: NASA/JPL-Caltech

Today in Science

Aphelion

The Earth orbits around the sun not in a perfect circle, but in a somewhat elliptical shape. That means that while the Earth is, on average, 93 million miles away from the sun, its exact distance varies based on where in the orbit it is. Today at 19:41 UTC (3:41 p.m. EDT), the Earth is at aphelion, meaning it is as far from the sun as it gets during its yearlong orbit around the sun—94,508,960 miles away.

The Earth is closest to the sun (at perihelion) in early January, when it is only 91,402,560 miles away. Because the Earth's orbit is nearly a perfect circle, though, Earth's distance from the sun at perihelion is only 3% closer than at aphelion.

Neither aphelion nor perihelion are set dates on the calendar. Currently they occur in early July and January. However, the anomalistic year (measured from perihelion to perihelion) is approximately 25 minutes longer than the tropical year (measured from equinox to equinox) upon which our calendar system is based. That means roughly every 58 years, perihelion and aphelion regress, or move forward a calendar day. Aphelion and perihelion will move all the way around the calendar in about 21,000 years.

Learn more about the Earth, the sun, and orbits with these Science NetLinks resources:


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