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Definitions Fact-pak
Kepler's Laws
The planets move in ellipses around the Sun, which is at one focus of the ellipse. The planets sweep out equal areas in equal times, relative to the solar focus. The rate of rotation is proportional to the distance from the Sun, such that p2/a3 is a constant. (p is the period of revolution and a is the mean Solar distance)
Newton's Universal Law of Gravity
...states that all masses in the Universe are attracted to all other masses in the Universe and that this attractive force is proportional to the respective masses of the objects concerned and is inversely proportional to the square of the distances between them. This results in the formula: Fg=Gm1m2/r2
Where Fg is the gravitational force, m1 and m2 are the masses of two objects attracting one another, r is the distance apart of the two bodies (measured between their centres of gravity), G is the Gravitational Constant and its value is 6.67 x 10-11 Nm2kg-2.
Albedo How reflective an object is. It is the ratio of reflected to incoming light or radiation
Diurnal Motion The daily movement of astronomical objects across the sky
Siderial Time Time monitored with reference to the stellar background
Ecliptic The imaginary plane on which the Earth and Sun jointly lie
Ellipticity The amount or degree that something - eg an orbit or planet - varies from a circle towards an ellipse
Rift Valley A huge flat-bottomed, steep-sided depression in the landscape, often associated with tectonic activity
Caldera The crater of a volcano
Tidal Lock A process that makes planets and moon harmonise their rotation and orbit
Celestial Sphere The sky sphere around the Earth that contains the stellar background
Sol A Martian Day 24 hours 37 minutes 22 Seconds
Meridian A line of longitude on the celestial sphere
Precession The slow drift of the poles due to the gyroscopic action of the planet
Obliquity The angle of tilt of a planet's axis relative to the ecliptic
Eccentricity The varience of an elliptical orbit from a perfect circle
Solstice The limits of north and south apparent movement of the Sun
Vernal Equinox The moment in spring when the sun is over the equator
Autumnal Equinox The moment in autumn when the sun is over the equator
Aphelion Farthest point from the Sun for an object in solar orbit
Perihelion Closest approach to the Sun for an object in solar orbit
Apogee Farthest point in an orbit from the Earth
Perigee Closest approach in an orbit to the Earth
Stellar Magnitude The brightness of an object, usually a star, in the sky
Astronomical Unit AU The distance from Earth to the Sun
Light-year Distance light travels in one year
Tharsis Bulge A large area of Mars which rises several kilometres above the average surface level of the planet
Terraforming Remodelling and engineering a planet on a global scale to make it habitable
Asteroid A small rocky celestial body orbiting the Sun
Crustal Dichotomy Division between two parts of crust, which appear very different from each other (Mars)
Mare A large featureless area of of a planet or moon resembling an ocean (however, not containing liquid)
Planitia Literally plain
Mons Literally mountain or hill
Splat Crater Also known as rampart craters, these are formed by impact into wet or icy soil or regolith
Ray Crater Ray craters formed in dry soil or regolith, so called because material from them sprays out leaving ray-like trails
Regolith The top soil of a planet or moon
Plate Tectonics The movement of continents and ocean floors about the surface of the planet, caused by deep geological processes
Meteor All the individual grains of rock and dust in space are called "meteoroids" while they are in space; when they interact with the Earth and its atmosphere that they receive different names: meteors are very small, often smaller than sand grains, and burn up in the atmosphere, producing "shooting stars"
Meteorites Are meteoroids (see above), but are massive enough to reach the ground, they are stony, stony-iron or iron lumps
Mantle The material surrounding the core of a planet, beneath the crust. On terrestrial planets this is rocky, probably silicate
Core The centre of a planet. The three terrestrial planets have high-density iron-rich cores. Earth has a liquid metal outer core, containing about 10 percent by mass of non-metal, and a solid, probably iron-nickel, inner core
Van Allen Belts A zone of radiation around the Earth, where charged particles are trapped within the magnetic field. These particles are collected from the Solar Wind, Cosmic Rays, and Earth
The Site uses as far as possible the mathematical conventions of the SI System, which has been adopted by over 90% of countries. Figures and values are also given in many cases, in non-SI units but these should be considered as approximate conversions, and not true values.
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EXPLORING MARS 
