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Review Questions

Space is a time machine a. Looking out into space is looking back in time. b. This is due to the finite speed of light, 300000 km/sec. c. You see objects as they were when the light left them. For very distant objects, this can be
d = v t, light years a. Distance traveled is speed (velocity) times the travel time. b. For light, the speed is 300,000 km/s, a constant of nature. c. In one year, light travels a distance d = v t = (300,000)(365)(24)(3600) = 9.
Scientific notation a. This notation is useful for writing the very large and very small numbers we often encounter in science. b. The number is written in two parts: a number between 1 and 10, and an
Constellations a. The IAU has defined 88 constellations which divide up the entire sky. b. The stars in a constellation may have no physical association with each other. c. A star is named by a Greek letter denoting its relative brightness in the con
Phases of planetary objects a. The Sun is the sole source of visible light in the Solar System. An object's phase depends on the angle between the observer, the object, and the Sun. b. Phases of the Moon.
Lunar eclipses a. Because the plane of the Moon's orbit around the Earth is tilted about 5 degrees from the plane of the Earth's orbit around the Sun, the Moon usually misses the Earth's shadow at full phase and does not cover the Sun at new phase, but there are occa
Solar eclipses a. A _____ happens when the Moon covers the Sun. b. There are two parts to shadows cast by the Sun. The umbra is the darkest part of the shadow; from within the umbra, an observer could not see any part of the bright surface of the Su
Diurnal motion a. During the course of the night, stars appear to move in circles around the celestial poles. b. Stars close enough to the pole are always visible to an observer at a mid-latitude (like Fayetteville), and neither rise above the horizon
Celestial poles a. Polaris is currently a very nice North Star, within 1 degree of the true pole. b. There is currently no good South Star (but there will be far in the future).
Precession Because of gravitational torques on the Earth, its rotational axis sweeps out a conical path in the sky over a period of about 26,000 years.
The small angle equation α/206265 = d/D
Celestial coordinates The Earth's poles have latitudes of 90 degrees N and S. The Earth's equator has a latitude of 0. This system, when projected onto the sky, gives the celestial coordinates of declination and right ascension for objects in the sky.
Effect of latitude Latitude is measured N or S from the equator (0 degrees) to the observer.
Effect of longitude Longitude is measured E or W of Greenwich, England (0 longitude) Traditionally, longitude is measured in time units like hours
Created by: at21