1. Unit 2 Vocabulary

2. 1.) Astronomy – the scientific study of the universe; it includes the observation and interpretation of celestial bodies and phenomena. 2.) Geocentric – describes the concept of an Earth-centered universe. 3.) Heliocentric – describes the view that the Sun is at the center of the solar system

3. 4.) Ellipse – an oval; the shape that the orbits of the planets are thought to be. 5.) Astronomical Unit (AU)— the average distance from Earth to the Sun 6.) Rotation – the spinning of a body, such as Earth, about its axis (causes day/night)

4. 7.) Revolution – the motion of one body around another, as Earth around the Sun (causes the year). 8.) Precession – a slow motion of Earth’s axis that traces out a cone over a period of 26,000 years. 9.) Solar Eclipse – an eclipse of the Sun; occurs when the moon moves in a line directly between Earth and the Sun, casting a shadow on Earth.

5. 10.) Lunar Eclipse – an eclipse of the Moon; occurs when the moon passes through Earth’s shadow. 11.) Terrestrial Planet – any of the Earth-like planets; Mercury, Venus, Earth, and Mars 12.) Jovian Planet – huge gas-giants with relatively low densities; Jupiter, Saturn, Uranus, and Neptune

6. 13.) Nebula – a cloud of gas and/or dust in space. 14.) Meteoroid – a small, solid particle that travels through space. 15.) Meteor— the luminous phenomenon observed when a meteoroid enters Earth’s atmosphere and burns up; also called a shooting star

7. 16.) Meteorite – and portion of a meteoroid that reaches Earth’s surface. 17.) Electromagnetic Spectrum – the arrangement of electromagnetic radiation according to wavelength (Radio waves, Infrared waves, Visible Light, UV, X-Rays, Gamma Rays) 18.) Light-Year – the distance light travels in a year, about 9.5 million kilometers

8. 19.) Radiation – the transfer of energy (heat) through space by electromagnetic waves). 20.) Galaxy – a group of stars, dust, and gases held together by gravity. 21.) Aphelion – the place in the orbit of a planet where the planet is farthest from the Sun. 22.) Perihelion - the point in the orbit of a planet where it is closets to the Sun.

9. 23.) Perigee – the point at which the Moon is closest to Earth. 24.) Apogee – the point at which the Moon is farthest from Earth. 25.) Nuclear Fusion – the way in which the Sun produces energy; when nuclei combine; tremendous amounts of energy is released.

10. 1.) Cosmic Rays – immensely high energy radiation, mainly originating outside the Solar system 2.) Kepler’s Laws – support the theory and understanding of our solar system. a.) The path of each planet is an ellipse, the Sun at the focus (center) b.) Each planet revolves in an imaginary line over equal areas (Must go faster when farther from the Sun and slower when closer to the Sun) c.) The time it takes the planet to orbit the Sun (orbital period) is proportional to the distance from the Sun.

11. 3.) Nutation – a periodic oscillation of the earth's axis that causes the precession of the poles to follow a wavy path rather than a circular path. 4.) Barycenter – is the center of mass of two or more bodies that are orbiting each other 5.) Nuclear Fission – occurs when the nuclei split into smaller nuclei and emit neutrons and heat energy.