Astronomy — Revolution and rotation
Revolution and rotation
- The planets of our solar system revolve around the Sun in orbits that lie close to a common plane. The orbit of Mercury, the closest planet to the Sun, is tipped 7 degrees compared to Earth’s orbital plane, and Pluto’s is tipped 17.2 degrees. The rest of the planets’ orbital planes are inclined by no more than 3.4 degrees. Thus, the solar system is basically disk-shaped.
- The rotation of the Sun and the planets on their axes also seems related to this disk-shaped system. The Sun rotates with its equator inclined only 7.25 degrees to the Earth’s orbit, and most of the other planet’s equators are tipped less than 30 degrees. The rotation of Venus and Uranus are peculiar, however. Venus rotates backward compared with the other planets, and Uranus rotates on its side (with its equator almost perpendicular to its orbit).
- Apparently, the preferred direction of motion in the solar system — counter-clockwise as seen from the north – is also related to its disk shape. All the planets revolve counterclockwise around the Sun, and with the exception of Venus and Uranus, they rotate counter-clock wise on their axes.
- With few exceptions, revolution and rotation in the solar system follow a disk theme. Sharp eyes, however, might detect another significant pattern in the planetary orbits. Each planet is a little less that twice as far from the Sun as its inward neighbor. In 1766 Johann Titius found a simple sequence of numbers that reproduces these distances, and because it was first reported by Johann Bode in 1772, the sequence is now known as the Titius-Bode rule.
- No one knows why the Titius-Bode rule generates the distances of the planets, but it is often interpreted to mean that the planets were not formed by some random process.
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