# Diameter of the Earth's Orbit

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Bibliographic Entry Result
(w/surrounding text)
Standardized
Result
Feather and Snyder. Earth Science. New York: Glencoe, 1999: 617. "Earth gets closest to the sun-about 147 million km away on January 3. The farthest point in Earth's orbit is about 152 million km away from the sun and is reached on July 4." 294–304 million km
World Book Encyclopedia. Chicago: 2004 Edition: 17. "In January, Earth is 147.1 million km from the sun and in July it is 152.1 million km from the sun." 294.2–304.2 million km
Is the distance from the Earth to the Sun changing? Curious About Astronomy. Cornell University. "However, over the entire main sequence lifetime of the Sun (about 10 billion years), the Sun will only lose about 0.1% of its mass, which means that the Earth should move out by just ~150,000 km (small compared to the total Earth-Sun distance of ~150,000,000 km)." 300 million km
The World Almanac: 1986. "Distance from the sun
Perihelon 91.4 million miles"
294 million km
The New Book of Knowledge. New York: Grolier, 2001: 10. "Distance from the sun (average) 93,000,000 miles" 300 million km

The path of the Earth around the sun is called the Earth's orbit. The orbit lies on an imaginary flat surface that cuts through the sun. This surface is the earth's orbital plane. Astronomers call an orbit the path of any object whose motion is controlled by the gravitational pull of another object. They call the more massive of the two objects the primary and the less massive one the secondary. The moon is a secondary that revolves around the earth, its primary.

The orbit of a secondary object is a closed curve called an ellipse. Perfectly circular orbits rarely occur. The farther a planet is from the sun, the longer it takes to orbit. In an elliptical orbit, the primary is not in the center of the ellipse. This causes the secondary to travel closer to the primary at certain times than at others. The Earth's axis does not stick straight up from the orbital plane. It tilts about 23½ degrees from the straight-up position, which causes the change of seasons.

It takes 365¼ days, one year, for the Earth to go around the Sun once. This means that the Earth is rushing through space around the sun at a rate of about 29,000 m/s (66,000 mph)! The distance between the Earth and the sun changes as the year progresses. Earth is closest to the sun on January 3 and farther from the sun on July 4, so the size of the orbit varies.

Cherisse Barnes -- 2004