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Science terms 11.2

Zenith The point directly overhead of an observer.
Nadir The point directly below an observer.
Meridian The circle on the celestial sphere that connects both poles and intersect the observer zenith and nadir.
Transit An occurrence taking place when an object crosses over an observers meridian.
Upper transit A transit in the half of the meridian containing the zenith.
Lower transit A transit in the half of the meridian containing the nadir.
Sidereal day A rotation of the earth in relation to the stars, this is the actual time it takes for the earth to rotate. This time is used by astronomers, its day lasts 23h 56m 4s.
Apparent solar day The time used in relation to the upper transits of the sun. It varies because the earths speed varies, and rotation and orbit cause changes in the time it takes the sun to be in its upper transit.
Mean solar day The average time of the different lengths of solar days.
Equation of time The difference in mean solar time and apparent solar time.
Standard solar time Time used today in which the mean solar time is used and the world is divided into 24 time zones each an hour apart.
Coordinated universal time (UTC) The time in the UCT is the mean solar time at the prime meridian (0 longitude).
Summer time Time used in some countries in which you set your clock ahead one hour on the second Sunday in march at 2 am.
A.M. Ante meridiem-The hours before noon classified as the first 12 hours of the day.
12-hour time The time used by Americans dividing the days into two periods of twelve hours.
P.M. post meridiem the after noon hours classified as the last twelve hours of the day.
24-hour time Time more common than twelve hour time used in other nations as well as the military.
Solar year The amount of time it takes the earth to orbit the sun.
Lunar year Years used by few people, and made up of twelve lunar months.
B.C The time used for all events occurring before the birth of Jesus Christ.
A.D. The time used for all events coming after the birth of Jesus Christ.
Week The only measure of time not based upon the stars, but rather the week of creation.
Calendar A device used to divide the year into months and days.
Julian calendar The Roman calendar instituted by Julius Caesar based on a solar year as opposed to a lunar year.The calendar was designed by Sosigenes Alexandria, he created it from a modified Egyptian calendar.The english calendar names come from this calendar.
Gregorian calendar The calendar used today, instituted by Pope Gregory 13th.
Equinox The point, or point in time when the ecliptic intersects the celestial equator.
Vernal equinox The point when the sun crosses the celestial equator from South to North
Autumnal equinox The point when the sun crosses the celestial equator from north to south.
Procession of the equinoxes The "wobbling" of the earth's axis.
Solstice A point on the ecliptic between the equinoxes.
Tropics The points on the earth on which the sun shines directly over.
Frigid zones Regions of the earth which experience of at least one day of darkness and one day of light.
Temperate zones The zones between the frigid zones and the Tropics.
Created by: MarciM31601