Our Solar System .... An Overview.
Our solar system consists of an average star we call the Sun ,the planets Mercury, Venus, Earth, Mars,
Jupiter, Saturn, Uranus, and Neptune,and the dwarf planets Pluto, Eris and Ceres.
It includes: the satellites of the planets; numerous comets, asteroids, and meteoroids; and the interplanetary medium.
The planets, most of the satellites of the planets and the asteroids revolve around the Sun in the same direction, in nearly circular orbits.
When looking down from above the Earth's north pole, the planets orbit in a counter-clockwise direction.
When viewed from the side the planets orbit the Sun in or near the same plane, called the ecliptic.
Pluto is a special case in that its orbit is the most highly inclined (18 degrees) and the most highly elliptical of all the planets.
Because of this, for part of its orbit, Pluto is closer to the Sun than is Neptune.
The axis of rotation for most of the planets is nearly perpendicular to the ecliptic.
The exceptions are Uranus and Pluto, which are tipped on their sides.
Obliquity of the Nine Planets.
This illustration shows the obliquity of nine of the planets.
Obliquity is the angle between a planet's equatorial plane and its orbital plane.
By International Astronomical Union (IAU) convention, a planet's north pole lies above the ecliptic plane.
By this convention, Venus, Uranus, and Pluto have a retrograde rotation,
or a rotation that is in the opposite direction from the other planets.
Composition Of The Solar System
The Sun contains 99.85% of all the matter in the Solar System.
The planets, which condensed out of the same disk of material that formed the Sun,
contain only 0.135% of the mass of the solar system.
Jupiter contains more than twice the matter of all the other planets combined.
Satellites of the planets, comets, asteroids, meteoroids, and the interplanetary medium constitute the remaining 0.015%.
The Sun is the richest source of electromagnetic energy (mostly in the form of heat and light) in the solar system.
The Sun's nearest known stellar neighbour is a red dwarf star called Proxima Centauri, at a distance of 4.3 light years away.
The whole solar system, together with the local stars visible on a clear night, orbits the center of our home galaxy,
a spiral disk of 200 billion stars we call the Milky Way.
The Milky Way is in 'The Local Group' of galaxies and has two small galaxies orbiting it nearby, which are both easily
visible from the southern hemisphere.
They are called the Large Magellanic Cloud and the Small Magellanic Cloud.
The nearest large galaxy is the Andromeda Galaxy. It is a spiral galaxy like the Milky Way
but is 4 times as massive and is 2 million light years away.