Earth Revolution

by Jerry Coffey on March 25, 2010

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Earth Revolution

Our blue marble. Credit: NASA

There are two types of Earth revolution: around its axis and around the Sun. The Earth revolves around the Sun once every 365.242199 mean solar days(that’s why we have leap years). The Earth orbits the Sun at a speed of 108,000 km/h. It revolves(rotates) on its axis once during an approximate 24 hours. The actual day is not exactly 24 hours, but that is the stuff for another article(there will be a link to it at the end of this one).

The Earth is never in the same exact same position from day to day. It moves closer to, and further away from, the Sun. Earth’s perihelion(147,098,074 km) occurs around January 3, and the aphelion around July 4 (152,097,701 km) . The changing Earth-Sun distance results in an increase of about 6.9% in solar energy reaching the Earth at perihelion as related to aphelion. The southern hemisphere is tilted toward the Sun at about the same time that the Earth reaches the closest approach to the Sun, so the southern hemisphere receives slightly more energy from the Sun than does the northern over the course of a year.

The Earth rotates around its axis by moving to the east. The Earth actually rotates 360.9856° in a mean solar day at a speed of 1,674.4 km/h. Earth’s rotation period relative to the Sun (its mean solar day) is 86,400 mean solar seconds. Earth’s rotation period relative to the fixed stars, called its stellar day is 86,164.098 903 691 seconds of mean solar time. Earth’s rotation period relative to the moving mean vernal equinox(its sidereal day) is 86,164.090 530 832 88 seconds of mean solar time, making it slightly longer than the stellar day. Over millions of years, the rotation is significantly slowed by gravitational interactions with the Moon(tidal acceleration/deceleration). Some large scale events, such as the high scoring earthquakes, have caused the rotation to speed up by around 3 microseconds. The speed of the rotation of Earth has had various effects over time, including the Earth’s shape, climate, ocean depth and currents, as well as tectonic forces.

This link takes you to a good article about Earth’s rotation. This is the NASA webpage all about Earth. Here on Universe today we have a great article about the Earth’s revolution. Astronomy Cast offers a good episode about solar system positions.

References:
NASA: Why Do We Study the Sun?
NASA Eclipse

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