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Astronomy 1021
Ch. 2
Question | Answer |
---|---|
Constellation | One of the stellar patterns identified by name, usually of mythological gods, people, animals, or objects. Also, the region of the sky containing that star pattern. |
Asterism | A named grouping of stars that is not one of the recognized constellations. |
Magnitude scale | The astronomical brightness scale. The larger the number the fainter the star. |
Apparent visual magnitude (m, v) | A measure of the brightness of a star as seen by human eyes on Earth. |
Flux | A measure of the flow of energy out of a surface. Usually applied to light. |
Celestial sphere | An imaginary sphere of very large radius surrounding Earth to which the planets, stars, Sun, and Moon seem to be attached. |
Scientific model | A concept that helps you think about some aspect of nature without necessarily being true. |
Precession | The slow change in orientation of the earth's axis of rotation. Once cycle takes nearly 26 000 years. |
Rotation | Motion around an axis passing through the rotating body. |
Revolution | Orbital motion about a point located outside the orbiting body. |
Ecliptic | The apparent path of the Sun around the sky. |
Solar eclipse | The even that occurs when the Moon passes directly between Earth and the Sun, blocking your view of the Sun. |
Umbra | The region of a shadow that is totally shaded. |
Penumbra | The portion of a shadow that is only partially shaded. |
Annual eclipse | A solar eclipse in which the solar photosphere appears around the edge of the Moon in a bright ring, or annulus. Features of the solar atmosphere cannot be seen during an annual eclipse. |
Lunar eclipse | The darkening of the Moon when it moves through Earth's shadow. |
Saros cycle | An 18-year, 11 1/3 day period after which the pattern of lunar and solar eclipses repeats. |
Declination | The angular distance of an object on the celestial sphere measure north (+) or south (-) from the celestial equator. |
Right ascension | The angular east-west distance of an object on the celestial sphere measure from the vernal equinox; measured in hours, minutes, and seconds rather than angular degrees. |
Solar day | The average time between successive crossings of the Sun on the local meridian (24 hours). |
Sidereal day | The time between successive crossings of any star on the local meridian (23 hours, 56 minutes, 4.09 seconds). |
Synodic month | The time for a complete cycle of lunar phases (about 29.5 days). |
Sidereal month | The time for the Moon to orbit Earth once relative to any star (~27.3 days). |
Sidereal year | The time for Earth to complete one full orbit around the Sun relative to any star. |
Tropical year (solar year) | The time between successive spring (or autumnal) equinoxes. |
Apparent solar time | Time measured by the location of the Sun in the local sky such that noon is when the Sun crosses the meridian. |