For an explanation, see the main splats page

The principles of the solar system

• Every body in the solar system has an albedo, though some have less than others. For small bodies, the albedo depends only on what they are made of.

• The closest point of a planet's orbit to the sun is called the perihelion, the most distant point of a planet's orbit from the sun is called the aphelion.

• Orbiting bodies obey Kepler's laws of planetary motion, whether they are planets around the Sun, or moons (or spacecraft) orbiting one of the planets.

• The planets obey Kepler's three laws of planetary motion, which can all be shown to follow naturally from the operation of gravitational forces.

• Kepler's first law says that all planets revolve around the Sun in elliptical orbits, with the Sun lying at one focus of the ellipse traced out.

• Kepler's second law says that for any planet, a radius line joining that planet to the Sun sweeps out equal areas of space in equal lengths of time.

• Kepler's third law says that the square of the period of revolution (year) of a planet is proportional to the cube of its mean distance from the Sun.

• In 1626, Godfried Wendilin verified Kepler's laws of planetary motion for the moons of Jupiter, showing that the laws apply to all orbiting bodies.

• In 1684 Isaac Newton proved that planets moving under an inverse-square force law obey Kepler's laws of planetary motion, that gravity is the same everywhere.

• In 1787, William Herschel found the planet Uranus, which he called a star, and claimed to have found volcanoes on the surface of the moon, but he got better.

• In 1613 Galileo Galilei used sunspots to demonstrate the rotation of the sun on its axis, and he also outlined the principle of inertia at the same time.

• In 1675 Giovanni Cassini reported his discovery that Saturn has separated rings and that they must necessarily be composed of small orbiting objects.

• We can measure the distances to the moon using radar transmission and reflection, though other methods can be used to get a reasonable estimate of the distance.

• Our solar system is made up of the Sun and nine planets and many smaller bodies, including asteroids, comets, moons, dust and Kuiper Belt Objects.

• Planets form from dust and debris from old supernovae that is drawn into the gravitational field of a star that is forming, where something pulls it together.

• Around 1640, René Descartes used a strange notion of vortices to present a model of the solar system which matched Galileo's, but avoided annoying the Church.

• In 1755 Immanuel Kant proposed his theory that the universe formed from a spinning nebula in an infinite hierarchy, which seemed like a good idea at the time.

• In 1905, Percival Lowell suggested there might be a ninth planet beyond Neptune, which he called Planet X. He photographed it before he died, but never saw it.

• In 1977, James L. Elliot discovered five rings around the equator of the planet Uranus, by the occultation of a star. Voyager 2 found four more rings in 1986.

• In 1980 Voyager 1 sent back pictures of Jovian system, in which researchers discovered the rings of Jupiter ,and these were further investigated by Voyager 2.

• Orbits are elliptical. Very rarely, the ellipse may be close to circular, but the circle remains just a special form of the ellipse, with equal semi-axes.

• Gravity acts everywhere: while people say that things in space are weightless, that is only because the entire frame is responding to gravity in the same way.

• Asteroids are relatively small bodies orbiting the sun, some of them in eccentric orbits that cross the Earth's. Some asteroids are large enough to have moons.

• In 1757 The Catholic Church removed Galileo Galilei's Dialogue on the Two Chief World Systems from its list of banned publications, after more than a century.

• There are places, the Lagrangian points, where objects may 'float in space', because they are points of stability where different gravitational fields balance.

This file is http://members.ozemail.com.au/~macinnis/scifun/, first created on February 23, 2009. Last recorded revision (well I get lazy and forget sometimes!) was on February 23, 2009.

©The author of this work is Peter Macinnis, who asserts his sole right to the product as it is packaged here, recognising that many of the ideas are common. You are free to use this as a model to do your own version. Copies of this whole file or site may be made and stored or printed for personal or educational use. You can contact me at macinnis@ozemail.com.au, but only if you add my first name to the front of that email address -- this is a low-tech way of making it harder to harvest the e-mail address I actually read.
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