Earth's orbit

Earth at seasonal points in its orbit (not to scale)

All astronomical objects in the Solar System, including the planets like Earth, orbit around the Solar System's centre of mass. Since the Sun constitutes 99.76% of this mass, the centre of mass is extremely close to the star.

Earth's orbit is the trajectory along which Earth travels around the Sun. The average distance between Earth and the Sun is 149.60 million km (92.96 million mi),[1] and one complete orbit takes 365.256 days (1 sidereal year), during which time Earth has traveled 940 million km (584 million mi).[2] Earth's orbit has an eccentricity of 0.0167.

As seen from Earth, the planet's orbital prograde motion makes the Sun appear to move with respect to other stars at a rate of about 1° (or a Sun or Moon diameter every 12 hours) eastward per solar day.[nb 1] Earth's orbital speed averages about 30 km/s (108,000 km/h; 67,000 mph), which is fast enough to cover the planet's diameter in 7 minutes and the distance to the Moon in 4 hours.[3]

From a vantage point above the north pole of either the Sun or Earth, Earth would appear to revolve in a counterclockwise direction around the Sun. From the same vantage point, both the Earth and the Sun would appear to rotate also in a counterclockwise direction about their respective axes.

History of study

Heliocentric Solar System
Heliocentrism (lower panel) in comparison to the geocentric model (upper panel)

Heliocentrism is the scientific model that first placed the Sun at the center of the Solar System and put the planets, including Earth, in its orbit. Historically, heliocentrism is opposed to geocentrism, which placed the Earth at the center. Aristarchus of Samos already proposed a heliocentric model in the 3rd century BC. In the 16th century, Nicolaus Copernicus' De revolutionibus presented a full discussion of a heliocentric model of the universe[4] in much the same way as Ptolemy had presented his geocentric model in the 2nd century. This "Copernican revolution" resolved the issue of planetary retrograde motion by arguing that such motion was only perceived and apparent. "Although Copernicus's groundbreaking book...had been [printed] over a century earlier, [the Dutch mapmaker] Joan Blaeu was the first mapmaker to incorporate his revolutionary heliocentric theory into a map of the world."[5]

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