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Topic: Sidereal day

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	Day - Wikipedia, the free encyclopedia
		A civil clock day is typically 86400 SI seconds long, but will be 86401 s long in the event of a leap second (or possibly 86399 s in the event of a reverse leap second, but a reverse leap-second has never happened yet).
		In astronomy, the sidereal day is also used; it is about 3 minutes 56 seconds shorter than the solar day, and close to the actual rotation period of the Earth, as opposed to the Sun's apparent motion.
		Days such as Christmas Eve, Hallowe'en, and the Eve of Saint Agnes are the remnants of the older pattern when holidays began the evening before.
	en.wikipedia.org /wiki/Day (1282 words)

	Sidereal day - Wikipedia, the free encyclopedia (Site not responding. Last check: 2007-11-05)
		An apparent sidereal day is the time it takes for the Earth to turn 360 degrees in its rotation; more precisely, is the time it takes a typical star to make two successive upper meridian transits.
		There are 366.2422 sidereal days in a tropical year, but 365.2422 solar days, resulting in a sidereal day of 86,164.09 seconds (or: 23 hours, 56 minutes, 4.09 seconds).
		A mean sidereal day is reckoned, not from the actual transit, but from the transit of the mean vernal equinox (see: mean sun).
	www.leessummit.us /project/wikipedia/index.php/Sideral_day (247 words)

	sidereal day (Site not responding. Last check: 2007-11-05)
		Astronomical day, a period equal to the mean solar day, but beginning at noon instead of at midnight, its twenty-four hours being numbered from 1 to 24; also, the sidereal day, as that most used by astronomers.
		Civil day, the mean solar day, used in the ordinary reckoning of time, and among most modern nations beginning at mean midnight; its hours are usually numbered in two series, each from 1 to 12.
		Mean solar day (Astron.), the mean or average of all the apparent solar days of the year.
	dictionaries.cc /sidereal_day (1441 words)

	Sidereal Time
		A solar day is the duration of one apparent rotation of the Sun around the Earth.
		Sidereal time is the measure of the hour angle of the vernal equinox.
		The local sidereal time is equal to the right ascension that passes through the local celestial meridian (a line in the sky from pole to pole that passes overhead) at that moment.
	home.att.net /~srschmitt/siderealtime.html (640 words)

	DAY - Definition (Site not responding. Last check: 2007-11-05)
		This is the period recognized by courts as constituting a day.
		The Babylonians and Hindoos began their day at sunrise, the Athenians and Jews at sunset, the ancient Egyptians and Romans at midnight.
		Law), certain stated days for the return of writs and the appearance of parties; -- so called because originally peculiar to the Court of Common Bench, or Bench (bank) as it was formerly termed.
	www.hyperdictionary.com /dictionary/day (1101 words)

	day - definition by dict.die.net
		See under Clock, Day, etc. Sideral time, time as reckoned by sideral days, or, taking the sidereal day as the unit, the time elapsed since a transit of the vernal equinox, reckoned in parts of a sidereal day.
		Thus, if this is the sun, the day (the interval between two successive transits of the sun's center over the same meridian) is called a solar day; if it is a star, a sidereal day; if it is the moon, a lunar day.
		Day The Jews reckoned the day from sunset to sunset (Lev.
	dict.die.net /day (534 words)

	day
		The simplest definition of a day's duration, and the one used in most sciences, including astronomy, is that it is 86,400 seconds as the second is defined in SI.
		Actually, the point on the celestial sphere that is used for measuring sidereal time is not a star, but the true vernal equinox, the point where the sun crosses from the southern celestial hemisphere into the northern celestial hemisphere each year.
		Because the vernal equinox itself moves (due to the precession of the earth's axis), the sidereal day is not quite the same as the period of earth's rotation with respect to a fixed direction in space.
	www.sizes.com /time/day.htm (1117 words)

	Timekeeping
		The diurnal motion of the sky caused by the rotation of the Earth on its axis defined the day, the year was defined by the motion of the Earth on its orbit about the Sun, and the month was defined in relation to the revolution of the Moon about the Earth.
		The sidereal day is defined to be the length of time for the vernal equinox to return to your celestial meridian.
		It is this almost 4 minute per day discrepancy that causes the difference in sidereal and solar time, and is responsible for the fact that different constellations are everhead at a given time of day during the Summer than in the Winter.
	csep10.phys.utk.edu /astr161/lect/time/timekeeping.html (465 words)

	The Sirius Research Group (Site not responding. Last check: 2007-11-05)
		According to equation 2, the 9.12 ms longer sidereal day causes an increase of 1223 s in the length of the 360° orbit of the Earth around the sun, as compared to equation 1.
		It was said that the difference between the mean sidereal day of 86164.0905382 s and the mean solar day of 86400 s is exactly 235.9094618 s.
		If the mean sidereal day varies due to oscillations of the axis of rotation, logically the same variations MUST occur relative to the sun.
	siriusresearchgroup.com /artikel/Siriusyear.shtml (1158 words)

	Sidereal Time (Site not responding. Last check: 2007-11-05)
		A solar day lasts from when the Sun is on the meridian at a point on Earth until it is next on the meridian.
		Because of the Earth's revolution, a solar day is slightly longer than a sidereal day.
		A sidereal day lasts from when a distant star is on the meridian at a point on Earth until it is next on the meridian.
	astrosun2.astro.cornell.edu /academics/courses/astro201/sidereal.htm (276 words)

	SIDEREAL - Definition
		(Astron.) Measuring by the apparent motion of the stars; designated, marked out, or accompanied, by a return to the same position in respect to the stars; as, the sidereal revolution of a planet; a sidereal day.
		{Sideral time}, time as reckoned by sideral days, or, taking the sidereal day as the unit, the time elapsed since a transit of the vernal equinox, reckoned in parts of a sidereal day.
		This is, strictly, apparent sidereal time, mean sidereal time being reckoned from the transit, not of the true, but of the mean, equinoctial point.
	www.hyperdictionary.com /dictionary/sidereal (138 words)

	Aryabhatt : Vedic Astrology lessons (Site not responding. Last check: 2007-11-05)
		Said in another manner, a sidereal day is the time interval between two successive transits of a fixed star over the meridian of a place.
		A sidereal day is 3 minutes and 56 seconds (or roughly 4 minutes) shorter than the mean solar day.
		Time reckoned according to this method is called the sidereal time.Since the sidereal time considers the angular rotation of the earth in relation to the fixed stars of the zodiac, the earth will attain the same position with reference to the zodiac every day at the same sidereal time.
	www.aryabhatt.com /vediclessons/vediclesson5.htm (1963 words)

	Chapter 1, Section 3 (Site not responding. Last check: 2007-11-05)
		The difference between a solar and a sidereal day can be easily explained once we understand that Earth revolves around the Sun at the same time as it rotates on its axis.
		The reason for the difference between a solar day and a sidereal day is sketched in Figure 1.10.
		Thus, the interval of time between noon one day and noon the next (a solar day) is slightly greater than one true rotation period (one sidereal day).
	www.nordita.dk /~steen/fysik51/ast/astt8_files/AT40103.htm (1947 words)

	Calendars and their History
		By convention, the day is the smallest calendrical unit of time; the measurement of fractions of a day is classified as timekeeping.
		The principal astronomical cycles are the day (based on the rotation of the Earth on its axis), the year (based on the revolution of the Earth around the Sun), and the month (based on the revolution of the Moon around the Earth).
		Days are reckoned from sunset to sunset, so that day 1 begins at sunset on Saturday and ends at sunset on Sunday.
	astro.nmsu.edu /~lhuber/leaphist.html (8496 words)

	Solar and Sidereal Time (Site not responding. Last check: 2007-11-05)
		Although these two methods of timekeeping are based upon rotation of the earth, a Solar Day and a Sidereal Day differ in length.
		Sidereal time or star time is reckoned by the transit of the March equinox each rotational period.
		Since the sun crosses the meridian four minutes later each day, the solar day and the Sidereal day are not compatible.
	www.stargazing.net /mas/bill1.htm (220 words)

	Alternate Activity (Site not responding. Last check: 2007-11-05)
		That is, one day relative to the stars (a sidereal day) is not exactly the same as 24 hour day relative to the sun (a mean solar day).
		Your purpose in this activity is to determine the length of a sidereal day by observing the position of a single star from one night to the next.
		Finally, your goal is to develop an understanding of how the sidereal day time period affects how the night sky looks in the different times of the year.
	www.ccaurora.edu /astro/ast101/alternate4.htm (1700 words)

	Sidereal Time
		Rather than defining a Sidereal Day to be 24 hours, 4 minutes, we define Sidereal Hours, Minutes and Seconds that are the same fraction of a Day as their Solar counterparts.
		Sidereal Time divides one full spin of the Earth into 24 Sidereal Hours; similarly, the map of the sky is divided into 24 Hours of Right Ascension.
		More generally, the difference between an object's RA and the Local Sidereal Time tells you how far from the Meridian the object is. For example, the same object at LST=06:32:24 (one Sidereal Hour later), will be one Hour of Right Ascension west of your meridian, which is 15 degrees.
	kstars.sourceforge.net /handbook/ai-sidereal.html (543 words)

	Chapter Dawdle <i>to</i> Dead of D by Webster's Dictionary (1913 Edition)
		a period equal to the mean solar day, but beginning at noon instead of at midnight, its twenty-four hours being numbered from 1 to 24; also, the sidereal day, as that most used by astronomers.
		the mean solar day, used in the ordinary reckoning of time, and among most modern nations beginning at mean midnight; its hours are usually numbered in two series, each from 1 to 12.
		the mean or average of all the apparent solar days of the year.
	www.bibliomania.com /2/3/257/1195/22362/2.html (555 words)

	ASEN 5050 Project (page 1) - Andria Bilich
		The GPS satellites are in orbits around Earth creating orbital periods of one-half a sidereal day; however, geophysicists typically process data based on the solar day.
		Sidereal and solar day processing methods revealed small differences between the two methods, but these differences are not significant given the uncertainty in the measurements.
		Since the sidereal day is 4 minutes shorter than a solar day, the same GPS satellite will pass through the same portion of the sky (relative to a fixed observer) every 11 hours 58 minutes.
	ccar.colorado.edu /asen5050/projects/projects_2001/bilich (1006 words)

	Yavin IV Astronomy in a bit more depth
		We assume for simplicity's sake that this is the sidereal day.
		4745, the number of sidereal days in a sidereal year, is evenly divisible by the numbers 5, 7, 13, 49, and 73.
		The number 49 especially, being also the number of days in a sidereal month, could be expected to be prominent, as could also the number 7, since 7 times 7 results in 49.
	home.san.rr.com /crocuta/yavin/yavinastronomy.htm (1481 words)

	Calendar Date And Time To Julian Day And Sidereal Times
		For Financial dates and legal dates, days between dates, days before a date or days after a date, day of the week for a given date in history, involving the last 2 centuries, we suggest that you use our Julian to current day and date calculator.
		Sidereal time is the hour angle of the vernal equinox, the ascending node of the ecliptic on the celestial equator.
		Astronomers use local sidereal time because it corresponds to the coordinate right ascension of a celestial body that is presently on the local meridian.
	www.csgnetwork.com /siderealjuliantimecalc.html (486 words)

	Sidereal Clock
		A solar day is one in which the earth makes one rotation and the sun returns to the same place in the sky.
		A sidereal day is one in which the earth makes one rotation and the stars return to the same place in the sky.
		A sidereal day is a little bit shorter than a solar day because the earth is moving around the sun and it must turn a little bit farther each day to face the sun.
	www.bmumford.com /clocks/sidereal (508 words)

	Month (Site not responding. Last check: 2007-11-05)
		Lunar month, the period of one revolution of the moon, particularly a synodical revolution; but several kinds are distinguished, as the synodical month, or period from one new moon to the next, in mean length 29 d.
		36 s.; the sidereal, or time of revolution from a star to the same again, equal to 27 d.
		Month Among the Egyptians the month of thirty days each was in use long before the time of the Exodus, and formed the basis of their calculations.
	dictionaries.cc /Month (1046 words)

	Sidereal Day (Site not responding. Last check: 2007-11-05)
		A sidereal (pronounced sigh-dear'-real) day refers to the rotation of the Earth measured relative to the stars.
		It is the time it takes the Earth to rotate 360 degrees and is equal to 23 hours, 56 minutes and 4 seconds.
		The difference in the two "days" arises from the fact that during a day the Earth also travels nearly a degree further on its yearly trek around the Sun.
	liftoff.msfc.nasa.gov /academy/rocket_sci/satellites/sidereal.html (84 words)

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