Astronomy Glossary ( cont .)
DECLINATION One element of the astronomical coordinate system on the sky that is used by astronomers . Declination , which can be thought of as latitude on the earth projected onto the sky , is usually denoted by the lower-case Greek letter delta and is measured north (+) and south ( - ) of the celestial equator in degrees , minutes , and seconds of arc .
DIURNAL MOTION The apparent daily rotation of the sky from east to west . It is due to the real rotation of the earth from west to east .
ECOSPHERE The region around the sun in which the temperatures are neither too hot nor too cold for life to exist . Venus lies near the inner edge of the Ecosphere ; Mars is near the outer edge .
EQUATOR , CELESTIAL The projection of the earth ’ s equator on to the celestial sphere . It divides the sky into two equal hemispheres .
EQUATORIAL MOUNT A telescope mounting in which the instrument is set upon an axis which is parallel to the axis of the earth .
FACULAE Bright , temporary patches on the surface of the sun , usually associated with sunspots .
LIGHT YEAR The distance travelled by light in one year , which is approximately 9,460,000,000,000 kilometers .
ORBIT The path of an artificial or natural celestial body .
SATELLITE A secondary body moving round a planet .
SOLAR SYSTEM The system made up of the sun , the planets , satellites , comets , asteroids , meteoroids , and interplanetary dust and gas .
SPECTROSCOPE An instrument used to analyze the light from a star or other luminous object .
SUNSPOTS Darker patches on the sun . Their temperature is estimated to be as much as 2,000 degrees Celsius less than that of the area around them , so they appear darker by comparison .
UNIVERSAL TIME A measure of time used by astronomers . UT conforms to the daily motion of the sun .
ZENITH The point directly overhead in the sky .
LIGHT POLLUTION The emission of stray light or glare from street lights , buildings , cities and other man-made objects .