Io - Jupiter's closest and most volcanically active Galilean Moon

Definitions

There's a lot of big words used on this site and we hope to help define a few of them here:

Aphelion
In a orbit that is not perfectly round this would be the point at which the body is farthest to the object it orbits.
Astronomical Unit (AU)
The average distance from Sol to the Earth is equal to one astronomical unit or 1AU.
Body
The whole thing that we're talking about. e.g. The body of the earth would include the rock, water and air all in one.
Ecliptic
Most of the objects in the solar system formed in a flat disk around the equator of the sun. This disk is called the Ecliptic.
Heliocentric
An orbit with the sun at the center is considered a heliocentric orbit. e.g. The Earth orbits the Sun.
Heliopause
The boundary between our solar system and interstellar space where the Solar Wind no longer has any effect.
Heliosheath
The area between the Termination Shock and Interstellar Space where the Solar Wind still has some influence.
Hydrostatic Equilibrium
When an body gets big enough it's own gravity will start pulling it into a sphere. When a body has become a sphere (because of it's own gravity) it is in hydrostatic equilibrium.
Inclination
Also called Orbital Inclination. It is the angle between the orbital plane and the plane of reference. e.g. The Earth and Mars have the same orbital plane as the equator of the Sun (plane of reference) or a low inclination. Pluto's orbital plane is at a higher inclination to the Sun's plane of reference.
Interstellar Space
The space between the stars where they have no direct influence.
Lagrange Points
When one body orbits another there are certain positions in relation to each that are gravitationally stable. That is if something were to be placed in these positions they would could stay there, held in place by the two bodies the points relate to.
Leading Side
The side of a body facing the direction it is traveling.
Mass
This is a measure of how much stuff there is in a body. This is based on balance measures so the body will be the same mass no matter what planet it's on.
Orbit
When one object goes around another in a generally circular fashion. Some orbits are not perfectly round. Traveling once around and orbit is called one revolution.
Orbital Plane
If the orbit of an object was turned into a disk this would be the orbital plane.
Perehelion
In a orbit that is not perfectly round this would be the point at which the body is closest to the object it orbits.
Revolution
One orbit of a body around another body.
Rotation
One turn of a body on it's axis.
Temperature
We try to keep to Centegrade when quoting temperatures.
Sometimes we use Kelvin which uses the same incremental scale as Centegrade except that 0°K = -273°C.
If you want to convert to Farenheight, use this formula: ( °C x 1.8 ) + 32 = °F
Termination Shock
This is the boundary between the Solar System and the Heliosheath where the Solar Wind slows down significantly.
Tide Locked
When a body orbiting another body always shows the same side in realtion to the other body. This means the body rotates once for every revolution it makes. e.g. Earth's moon always shows the same side to Earth. So it makes one rotation on it's axis and one revolution around the Earth every 28 days.
Trailing Side
The side of a body facing away from the direction it is traveling.

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