| A | B |
|---|
| astronomical unit | the average distance between Earth and the sun |
| orbit | the elliptical path a body takes as it travels around another body in space |
| astronomy | the study of all physical objects beyond the Earth |
| cosmology | the study of the origin and future of the universe |
| ecliptic | the apparent path the sun takes across the celestial sphere |
| satellite | a natural or artificial body that revolves around a planet |
| space probe | a vehicle that carries scientific instruments to planets or other bodies in space |
| space shuttle | a reusable vehicle that takes off like a rocket and lands like an airplane |
| space station | a long-term orbiting platform from which other vehicles can be launched or scientific research can be carried out |
| electromagnetic spectrum | all the wavelengths of electromagnetic radiation |
| nuclear fusion | the process by which two or more nuclei with small masses join together or fuse to form a larger more massive nucleus |
| reflecting telescope | a telescope that uses curved mirrors to gather and focus light |
| refracting telescope | a telescope that uses a set of lenses to gather and focus light |
| asteroid | a small, rocky body that revolves around the sun |
| meteor | a streak of light caused when a meteroid or comet dust burns up in Earth's atmosphere before it reaches the ground |
| meteorite | a meteroid that reaches the Earth's surface without burning up completely |
| galaxy | a large grouping of stars in space |
| light-year | a unit of length equal to the distance that light travels through space in 1 year |
| Big Bang Theory | states that the universe began with a remendous explosion |
| comet | a small body of ice, rock, and cosmic dust loosely packed together that gives off gas and dust in the form of a tail as it passes close to the Sun |
| element | a pure substance that cannot be deparated or broken down into simpler substances by ordinary chemical means |
| ellipse | a closed curve in which the sum of the distances from the edge of the curve to two points inside the ellipse is always the same |
| nebula | a large cloud of dust and gas in interstellar space; the location of star formation |
| revolution | the elliptical motion of a body as it orbits another body in space |
| rotation | the spinning motion of a body on its axis |
| planetesimal | the tiny building blocks of the planets that formed as dust particles stuck together and grew in size |
| remote sensing | gathering data about something without actually being nearby |
| spiral galaxy | a galaxy with a bulge in the center and very distinctive spiral arms |
| irregular galaxy | a galaxy that does not fit into another category; one with an irregular shape |
| elliptical galaxy | a spherical or elongated galaxy with a bright center and very little dust and gas |
