Moody Descriptive Astronomy

34 terms by ramseycarr 

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geocentric

centered on the earth

direct motion

The normal eastward movement of a planet against the background of distant stars.

retrograde motion

The apparent backward motion of a planet against the background of stars.

epicycle

In Ptolemy's geocentric solar system, the small circle on which a planet moved.

deferent

In Ptolemy's geocentric solar system, the large circle on which a planet's epicycle moved around the Earth.

heliocentric

Centered on the Sun.

inferior planet

A planet that is closer to the Sun than the Earth.

superior planet

a planet that is farther from the sun than the earth.

conjunction

When a planet lines up with the Sun in the sky.

greatest elongation

The point where an inferior planet is as far away from the Sun as it can be (as seen from the Earth).

opposition

The point where a superior planet is as far away from the Sun as it can be (as seen from the Earth).

perihelion

The point in its orbit where a planet is nearest the Sun.

aphelion

The point in its orbit where a planet is farthest from the Sun.

semimajor axis

Half of the longest diameter across an ellipse.

force

a push or a pull

mass

A measure of how an object resists accelerating when acted upon by a force. It is proportional the amount of matter in an object.

weight

the measure of the force of gravity on an object

gravity

the force of attraction between any two objects that have mass

acceleration

any change in speed or direction of an object

occam's razor

The philosophical stand that says a simpler explanation is more likely to be correct than a complicated one.

lagrangian points

Points of gravitational stability in the orbit of a planet.

synchronous rotation

When one side of a body always faces the planet it revolves around.

solar nebula

the material from which the solar system was formed.

Jovian planets

planets that are Jupiter-like

density

mass divided by volume

chondrite

The first rock-sized bodies that formed in the solar nebula from dust grains.

planetesimal

The larger bodies that formed early in the solar nebula that were chemically differentiated.

aurora

The light produced when particles from the sun collide with atmospheric molecules.

accretion

the process of acquiring material

chemical differentiation

The sinking of denser elements to the center of a young molten planet.

terrestrial planets

earth like planets

plate tectonics

The movement of the Earth's crustal plates riding on top of the mantle.

greenhouse affect

The trapping of heat by carbon dioxide or other gases in the Earth's atmosphere.

condensation temperature

The temperature at which a substance in the vacuum of space solidifies.

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