# Earth Science Credit 9

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Earth Science Credit 9 Chapter 22 and 23 Early Astronomy and the Solar System Prentice Hall Earth Science

### Hipparchus

an early Greek astronomer. Best known for his star catalog. His star catalog determined the location of 850 stars and was divided into groups by brightness.

### Geocentric

System where the sun and all the planets orbit the Earth. The system believed by the Greeks.

### celestial sphere

In the geocentric model all the stars traveled on this transparent hollow sphere.

### Nicolaus Copernicus

An astronomer from the middle ages who was the first to propose a sun-centered solar system and that the earth was a planet.

### First law of planetary motion

The path of each planet around the sun is an ellipse, with the sun at one focus. The other focus is symmetrically located at the opposite end of the ellipse.

### Second law of planetary motion

Each planet revolves so that an imaginary line connecting it to the sun sweeps over equal areas in equal time intervals. If a planet is to sweep equal areas in the same amount of time, it must travel more rapidly when it is nearer the sun and more slowly when it is farther from the sun.

### ellipse

An oval or an elongated, closed curve that describes a planet's orbit around the Sun.

### Heliocentric

A model of the solar system where the planets orbit around the sun.

### Astronomical Unit (AU)

150 million kilometers or 93 million miles
the average distance between the Earth and the Sun.

### Orbit

the (usually elliptical) path described by one celestial body in its revolution about another

### law of universal gravitation

Every body in the universe attracts every other body with a force that is directly proportional to their masses and inversely proportional to the square of the distance between their centers of mass.

### Rotation

the turning of a body on its axis. This accounts for night and day on Earth.

### Revolution

the motion of a body along a path around a point in space. This accounts for tides as the Moon revolves around the Earth and for seasonal changes as the Earth revolves around the Sun.

### Solar Eclipse

The shadow cast by the Moon on the Earth. Only happens during the new-moon phase when the moon's orbit crosses the plane of the ecliptic (the plane that the Earth and Sun share). Happens approximately twice a year.

### Lunar Eclipse

the shadow cast by the Earth on the Moon. Only happens during the full-moon phase. Happens approximately twice a year.

### Phases of the Moon

Changes in the amount of the moon which appears to be lit. Light of the moon comes from the sun.
See http://visual.merriam-webster.com/astronomy/celestial-bodies/moon/phases-moon.php

### Maria

Dark regions of the moon's surface.

### Highlands

Light densely pitted regions of the Moon's surface.

### Giant Impact Hypothesis

A large body impacted the Earth and caused a large amount of crustal rock to break off and formed the moon. This accounts for the iron poor core of the moon.

### Terrestrial Planets

Mercury, Venus, Earth, and Mars are primarily made of rocks and silicate minerals and are much smaller than Jovian planets.

### Jovian Planets

Jupiter, Saturn, Neptune and Uranus are Giant Gas planets not primarily composed of solid material.

### Crater

a bowl-shaped depression formed by the impact of a meteorite

### Io

One of Jupiter's moons. One of the most volcanically active objects in the solar system.

### Mercury

Closest planet to the sun. No moons. Cratered surface from impacts. Smallest planet.

### Venus

Second planet from the sun. Dense atmosphere of Carbon Dioxide and Sulfuric Acid. No moons.

### Mars

Fourth planet from the sun. Two Moons. Stream-like deposits suggest the possibility of liquid water.

### Jupiter

Fifth planet from the sun. 63 moons. Larger than all other planets and moons combined.

### Saturn

Sixth planet from the sun. 53 moons. Second largest planet. It's moon Titan is the only moon with a substantial atmosphere.

### Uranus

seventh planet from the Sun; is large and gaseous, has a distinct bluish-green color, and rotates on an axis nearly parallel to the plane of its orbit.

### Neptune

eighth planet from the Sun; is large and gaseous, has rings that vary in thickness, and is bluish-green in color

### Pluto

A dwarf planet which was the smallest of the nine planets. Now not considered a planet because it shares its orbit with other planetoids. Has a single moon named Charon.

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