Glossary
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- Disk
- The visible surface of the Sun (or any heavenly
body) projected against the sky.
- Ecliptic
- The apparent path of the sun against the sky
background (celestial sphere); formally, the mean plane of the earth's orbit
about the sun.
- Equatorial
Plane
- An imaginary plane through the center of a planet
and the planet's equator.
- Escape
Velocity
- The velocity with which an object is able to escape
from a planet's gravitation field.
- Escarpments
- Long steep faces of a plateau.
- Gibbous
- Phase of moon (or planet) between first quarter and
full or between full and last quarter.
- Granulated
- Showing a pattern of small cells seen on the surface
of the Sun caused by the convective motions of the hot solar gas.
- Greenhouse
Effect
- Increase in temperature caused when incoming solar
radiation is passed but outgoing thermal radiation is blocked by the
atmosphere (carbon dioxide and water vapor are the major factors). Very
important on Venus and Earth, but very weak on Mars.
- Interplanetary
Magnetic Field
- The magnetic field carried with the solar
wind.
- Jovian
Planet
- Any of the four outer, gaseous planets: Jupiter,
Saturn, Uranus, and Neptune.
- Maria (plural)
- Literally "sea" (a very bad misnomer,
still in use for historical reasons); really a large circular plain.
(singular: "mare")
- Meteoroids
- A small rocky object orbiting the Sun; smaller than
an asteroid.
- Nuclear
Fusion
- A nuclear process whereby several small nuclei are
combined to make a larger one whose mass is slightly smaller than the sum of
the small ones. The difference in mass is converted to energy by Einstein's
famous equivalence E=mc2. This is the source of
the Sun's energy therefore ultimately of (almost) all energy on Earth.
- Perihelion
- The point in its orbit where a planet is closest to
the Sun. When referring to objects orbiting the Earth the term perigee is
used; the term periapsis is used for orbits around other bodies.
- Polar Caps
- High latitude regions on both hemispheres with open
magnetic field lines connecting directly to the interplanetary
magnetic field.
- Red
Dwarf Phase
- The phase of a star during which it has a relatively
low temperature and a smaller diameter compared its other subsequent phases.
- Retrograde
- Rotation or orbital motion in a clockwise direction
when viewed from above the north pole of the primary (i.e. in the opposite
sense to most satellites); the opposite of direct. The north pole is the one
on the same side of the ecliptic as the Earth's
north pole.
- Satellite
- A body that revolves around a larger body, may be
natural or man-made.
- Shepherding
Satellites
- Satellites which constrain
the extent of a planetary ring through gravitational forces. Also known as
Shepherd moons.
- Solar
Nebula
- The cloud of gas and dust that began to collapse
about 5 billion years ago to form the solar system.
- Solar Wind
- A tenuous flow of gas and energetic charged
particles, mostly protons and electrons -- plasma -- which stream from the
Sun; typical solar wind velocities are near 350 kilometers per second.
- Spectroscopy
- The study of spectra. Every atom can only emit or
absorb certain energies or wavelengths. Scientists use instruments called
spectrometers to study the location and spacing of emission and absorption
(spectral) lines in specific wavelengths to detect any atoms or molecules
that may be present in a target material (such as the surface of Mars).
- Terminator
- The dividing line between the illuminated and the un-illuminated
part of the moon's or a planet's disk.