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| astronomy | A natural science, is the study of celestial objects (such as stars, galaxies, planets, moons, asteroids, comets, and nebulae) and processes. |
| sun | The star around which the earth orbits. |
| moon | The natural satellite of the earth, visible (chiefly at night) by reflected light from the sun. |
| earth | The planet on which we live; the world; third rock from the sun. |
| dwarf planet | A celestial body resembling a small planet orbiting a star with mass to be rounded by its own gravity but not able to clear region of planetismals but not a satellite. |
| meteor | A small body of matter from outer space that enters the earth’s atmosphere becoming incandescent as a result of friction and appearing as a streak of light. |
| asteroid | A small rocky body orbiting the sun. |
| comet | A ball of ice and dust whose orbit is usually a long, narrow ellipse. When near the sun, a “tail” of gas and dust particles pointing away from the sun appears. |
| gravity | The attractive force between two objects; its magnitude depends on their masses and the distance between them. |
| revolution | The movement of an object around another object. |
| rotation | The spinning motion of a planet about its axis. |
| day and night | The middle layer of Earth’s atmosphere; the layer in which most meteoroids burn up. |
| phases of the moon | The lunar phase is the shape of the illuminated (sunlit) portion of the moon as seen by an observer on Earth. |
| planet | A celestial body moving in an elliptical orbit around a star. |
| season | Each of four divisions of the year (spring, summer, autumn, winter) marked by particular weather patterns and daylight hours, resulting from the earth’s changing position regarding the sun. |
| tides | The daily rise and fall of Earth’s waters on shores. |
| axis | An imaginary line that passes through the Earth’s center and the North and South poles, about which Earth rotates. |
| Ptolemy | Earth was the center of the universe with planets orbiting in epicycles or small circles, geocentric theory. |
| Aristotle | Geocentric theory but planets and stars movements are circular. |
| Copernicus | Earth rotates on its axis, the sun is the center of our solar system, heliocentric theory. |
| Galileo | Used advanced telescope to prove heliocentric theory but the church imprisoned him for life. |
| orbit | The path of an object as it revolves around another object in space. |
| rockets | A cylindrical projectile that can be propelled to a great height or distance by the combustion of its contents. |
| satellites | Any object that revolves around another object in space. |
| eclipse | An obscuring of light from one celestial body by the passage of another between it and the observer or between it and the source of light. |
| telescope | A device built to study distant objects by making them appear closer. |
| geocentric | A description of the solar system in which all of the planets revolve around Earth. |
| heliocentric | A description of the solar system in which all of the planets revolve round the sun. |
| terrestrial planets | The name given to the four inner planets: Mercury, Venus, Earth, and Mars. |
| gas giants | The name given to the first four outer planets: Jupiter, Saturn, Uranus, and Neptune. |
| Mercury | Planet nearest the sun, smallest planet, rocky planet. |
| Venus | Second planet from the sun, no natural satellite, brightest object in the night sky other than moon, rocky planet. |
| Mars | Fourth planet from the sun, second smallest planet, referred to as “Red Planet” because iron oxide (rust), rocky planet. |
| Jupiter | Largest planet in the solar system, fifth from the sun, composed of gas, visible from earth, gas giant. |
| Saturn | Second largest planet, sixth from the sun, composed of gas and liquid, most distant planet visible with the naked eye, surrounded by rings of ice particles, gas giant. |
| Uranus | Seventh planet from the sun, blue-green color, many satellites, ring of ice particles, gas planet. |
| Neptune | Eighth and farthest planet form the sun, fourth largest, most dense, noted as twin planet of Uranus, gas planet. |
