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	Precession of the Equinoxes - Crystalinks
		Precession of the equinoxes refers to the precession of Earth's axis of rotation in inertial space.It was discovered by Hipparchus that the positions of the equinoxes regress (move westward) along the ecliptic compared to the fixed stars on the celestial sphere.
		The precession of the equinoxes can cause periodic climate change (see Milankovitch cycles), because the hemisphere that experiences summer at perihelion and winter at aphelion (as the southern hemisphere does presently) is in principle prone to more severe seasons than the opposite hemisphere.
		Precession causes the cycle of seasons (tropical year) to be about 20.4 minutes less than the period for the earth to return to the same position with respect to the stars as one year previously (sidereal year).
	www.crystalinks.com /precession.html (1737 words)

	Archaeogeodesy, a Key to Prehistory III, by James Q. Jacobs
		Precession is the motion of the earth's axis of rotation gradually changing direction in reference to fixed celestial reference.
		Because the precession motion is retrograde, the axis realigns inclined towards the sun slightly before completion of an orbit, and therefore one year is shorter than one orbit by the inverse of the precession cycle, or about 1/25,780 (1/PR) in 2000.
		Lunar eclipses are a unique opportunity for every longitude to observe a celestial event the timings of which can be compared to locally-referenced time.
	www.jqjacobs.net /astro/aegeo_3.html (1665 words)

	Doors of Precession, The
		The bull, bees, and butterflies are also connected, by both Porphyry and Sophocles, with the chthonian goddess, or the goddess of the waters of death, and with the moon goddess, or the goddess of regeneration.
		Crescents and concentric circles on Neolithic pottery and on passage graves are lunar notations indicating the waxing moon, the full moon, the waning moon and the new moon in its four stages, respectively.
		Lunar nutation is represented on certain of the stone circles; nutation is actually seen where the full moon rises and sets at different declinations over a period of 18.6 years representing the changing position of the moon.
	www.themystica.com /mystica/articles/d/doors_of_precession_the.html (6131 words)

	Full moon: Definition and Links by Encyclopedian.com
		This precession causes the full moon cycle (fumocy) to be over a month longer than a sidereal year....in a Saros cycle.
		A full moon is the only time when a lunar eclipse is possible; at that time the moon may move through the shadow cast by the earth.
		Full moons are generally a poor time to conduct astronomical observations, since the bright reflected sunlight from the moon overwhelms the dimmer light from stars.
	www.encyclopedian.com /fu/Full-moon.html (1113 words)

	Precession - Wikipedia, the free encyclopedia
		In certain contexts, "precession" may refer to the precession that the Earth experiences, the effects of this type of precession on astronomical observation, or to the precession of orbital objects.
		Precession is the resultant of the angular velocity of rotation and the angular velocity produced by the torque.
		Discrepancies between the observed perihelion precession rate of the planet Mercury and that predicted by classical mechanics were prominent among the forms of experimental evidence leading to the acceptance of Einstein's Theory of Relativity, which predicted the anomalies accurately.
	en.wikipedia.org /wiki/Precession (1496 words)

	SOLAR AND LUNAR ECLIPSES
		Hiparco (194BC-120BC) discovered the Precession of the Equinoxes basically taking the total lunar eclipses near the Equinoxes and some tables for the Sun, and he improved the determination of the distance from the Earth to the Moon accomplished by Aristarco.
		The Lunar eclipse is objective because the moon illuminated by the Sun enters the umbra cone of the earth during the eclipse and does not receive the solar radiation.
		The lunar soil (of the visible face and in the part of the Moon that enters the umbra) suffers in a few hours a temperature fluctuation that oscillates between 130ºC and -100ºC. While the hidden face suffers this oscillation slowly every 29,5 days.
	www.geocities.com /s_perona/ingles/eclipse.htm (1423 words)

	PRECESSION & THE OBLIQUITY OF THE ECLIPTIC - TETRAKTYS RESEARCH CENTRE (Site not responding. Last check: 2007-11-02)
		In general, the term precession is used for the slow, periodic conical motion of the rotation axis of a spinning body.
		The component of precession caused by the Sun and Moon acting on the Earth's equatorial bulge is called lunisolar precession, and the component caused by the action of the planets is called planetary precession.
		Since the annual amount of the precession is inversely related to the obliqueness of the ecliptic plane, the derivatives of the two polynomials are expected to join at least at two abscissa points, when the ordinates are reduced to zero.
	www.tenspheres.com /researches/precession.htm (2527 words)

	Lunar Astronomy
		The first (on the left) can be interpreted as a space-time diagram of the moonset's daily displacement along the horizon: azimuth runs horizontally and time vertically upward, and the zigzag lines depict the back-and-forth motion of the moon along the horizon, for the rising (left half of diagram) and setting (right half) Moon.
		Other possible evidence for the Anasazi's lunar interests can be found at nearby Chimney Rock, where, as seen from the mesa-top pueblo, moonrise at major standstills is neatly framed by the twin rock towers giving the site its name (see Slide 1).
		A significant counterargument comes from the lunar astronomical practices of modern Pueblo people, who show great interest in the phases of the moon for time-keeping and yearly calendrical purposes, but not in its longer orbital or calendrical cycles.
	www.hao.ucar.edu /Public/education/archeoslides/slide_19.html (744 words)

	lunar2 (Site not responding. Last check: 2007-11-02)
		The Lunar Prospector spacecraft continues to perform very well and instruments are collecting good data.
		Several maneuvers were performed in the last week: a test pulse firing in reparation for the larger precession maneuver (planned for 3 days later), reorientation of the spin axis to improve the Sun angle, a circularization set of burns to adjust the orbit, and a spin trim to maintain nominal rate.
		On April 27 (DOY 117), the spin axis was precessed by 8.5 deg by firing 40.2-sec pulses.
	lunar.arc.nasa.gov /datavis/1998/05011000.htm (355 words)

	Center for Archaeoastronomy: A&E News Archive
		Because of precession, the time for the sun to move from one node to another is only 173.31 days.
		A directly related observation that could have provided the Maya with a clue to the precession of the moon's orbit is the dramatic change in the moon's monthly rise (or set) point.
		While the present evidence that Native American cultures of the United States were monitoring the 18.61 year cycle of the moon by means of the lunar standstills is not compelling, it is reasonably suggestive.
	www.wam.umd.edu /~tlaloc/archastro/ae3.html (787 words)

	Lunar orbit (Henry Spencer) (Site not responding. Last check: 2007-11-02)
		That only happens twice a month in a lunar polar orbit, because the orbit is roughly fixed in space (lunar orbital precession is negligible) as the Moon goes around in its orbit.
		The choice of lunar orbit is determined by exactly where the spacecraft is when the Moon arrives.
		It is marginally possible that a carefully-chosen and quite low orbit could exploit lunar mascons to do the same trick, given a complete and detailed understanding of the lunar gravitational field (which we don't have yet), but I wouldn't bet money on it.
	yarchive.net /space/orbits/lunar_orbit.html (1805 words)

	ASTR 121, O'CONNELL. Study Guide [Spring 2002]
		Precession, a wobbling motion of the Earth, complicates the interpretation of ancient observatories and records.
		C. Precession is a cyclical, long-period wobble in the orientation of the Earth's polar axis.
		The changes in the apparent size of the Moon and the slight "rocking" motion (known as libration) are caused by the fact that the lunar orbit is significantly non-circular in shape.
	www.astro.virginia.edu /class/oconnell/astr121/guide04-s02.html (1082 words)

	Hipparchus (astronomer) Summary
		He determined the annual amount of precession and from this obtained a nearly correct value for the duration of the tropical year (the period of the sun's rotation from equinox to equinox), which was too great by only 6 1/2 minutes.
		In discussing lunar latitude, he used data from the eclipse of 502, derived from cuneiform sources; he determined the inclination of the lunar orbit to the ecliptic to be 5°.
		Hipparchus observed (at lunar eclipses) that at the mean distance of the Moon, the diameter of the shadow cone is 2+½ lunar diameters.
	www.bookrags.com /Hipparchus_(astronomer) (8287 words)

	Lunar precession - Wikipedia, the free encyclopedia
		This precession period is equal to the time that number of sidereal months counted exceeds the number of anomalistic months counted by exactly one.
		This is to be distinguished from precession of the lunar nodes of the lunar orbit on the plane of the ecliptic.
		This is mainly caused by the oblation of the Earth; it is the period of the main nutation term in the orientation of the polar axis of the Earth.
	en.wikipedia.org /wiki/Lunar_precession (213 words)

	Precession--lesson plan #11
		A brief study of the precession of the equinoxes and of its possible link to the occurrence of ice ages.
		The precession of spinning satellites is undesirable, since it confuses the observations.
		The waving of these antennas gradually made the satellite precess around its spin axis, and the cone of precession grew wider, until in the end it was essentially flat and the satellite spun around an axis perpendicular to it, through its middle.
	www-istp.gsfc.nasa.gov /stargaze/Lprecess.htm (1723 words)

	The Full Moons Of Winter 1986, Alaska Science Forum
		The moon's orbit around the earth is inclined about 5 degrees from the earth's orbit around the sun, and it precesses around the earth, much as a tin plate or a quarter dropped crookedly onto a table will flutter about its axis before clattering to a halt.
		The new moon rises in the southeast and sets in the southwest, but as the lunar month wears on and the moon waxes, the rising point swings further and further to the left (east) and the setting point moves further and further to the right (west).
		In about another nine years, or half of the moon's precession period, you won't be able to see the full moon for a full 24 hours from anyplace south of the latitude of Barrow.
	www.gi.alaska.edu /ScienceForum/ASF7/758.html (545 words)

	Lunar Laser Ranging at McDonald
		The unique contributions already accomplished include a three orders-of-magnitude improvement in the accuracy of the lunar ephemeris, a several orders-of-magnitude improvement in the measurement of the variations in the Moon’s rotation, and the verification of the principal of equivalence for massive bodies with unprecedented accuracy.
		The lunar libration in longitude, with a period of only 2.9 yr, has a 69 yr beat with another term of similar period; a third mode of that libration has a 24 yr period with respect to the node; the dissipation term and the lunar obliquity have an 18.6 yr period.
		Finally, LLR is sensitive to the relative orientation of the equator, ecliptic and lunar orbit planes, presently at the 1.5 mas level, and improving with time, due to our being on a spinning Earth while the lunar orbit precesses along the ecliptic.
	www.csr.utexas.edu /mlrs/dda.html (2881 words)

	[No title]
		The Center for Lunar Research (CLR) was established in 1998 by the National Space Society in response to a de-emphasis by NASA on its lunar exploration program, decreasing government funding for lunar data analysis, and an NSS policy survey that identified lunar applications and development as a priority issue among our membership.
		Lunar Prospector's discovery of increased concentrations of hydrogen and the potential for water ice at the lunar poles prompted the investigations.
		He compared the calculated lunar hydrogen content with the lunar albedo measurements from the Clementine mission and found an approximately inverse linear relationship between the averaged hydrogen content and the lunar albedo value.
	www.nss.org /lunar (1439 words)

	The Myth of Babylonian Knowledge of Precession
		If the Babylonians (or some other cultural group) were aware of precession prior to 1000 BCE then they did not have the combined benefit of the concept of the ecliptic, an equally-divided 12-constellation zodiac, a geometrical perspective of the heavenly bodies, and the abstract moving points of the equinoxes and solstices.
		The expected easiest observations of precession (by some early culture at a continuously settled site) would perhaps be (1) the horizon and changes in the heliacal risings of stars, (2) the pole-star and the replacement of one by another over time, and (3) calendrical systems and the adjustments to such.
		It can be confidently stated that the phenomenon of precession was not identified by the Babylonians (and so it is out of the question that it was understood as a systematic continuous variation (i.e., that all stars have slow continuous motions parallel to the ecliptic) and that the rate of precession was measured).
	www.members.optusnet.com.au /~gtosiris/page9f.html (5115 words)

	Precession of a Gyroscope and Precession of the Earth's Axis
		This is therefore the simplified theoretical equation that describes the precession of a horizontal gyroscope.
		Scientists generally refer to a Luni-solar Precession, which is the total effect of these two, the 15.94 arc-seconds per year and the 34.45 arc-seconds per year, or a net effect of 50.39 arc-seconds per year.
		There is also lunar nutation, due to the "inequality" of the variations in the precession due to the Moon.
	mb-soft.com /public/precess.html (7872 words)

	Lecture Notes for Day 8 (Site not responding. Last check: 2007-11-02)
		Precession of the equinoxes results in a new zodiacal constellation at vernal equinox approximately very 2000 years.
		Eclipses: Solar eclipses occur at the time of new moon; lunar eclipses are associated with the full moon, when the moon slips into the earth's shadow.
		Lunar Standstills: Because of the 5.1 degree tilt of the moon's orbit with respect to the ecliptic, the moon may be anywhere within 5.1 degrees above or below the ecliptic.
	www.colorado.edu /APAS/APAS1010/lecture/day.8.html (675 words)

	The Sirius Research Group
		In the first case the rotational axis of the Earth is fixed and in the second case it precesses, whereby a full 360° orbit of the Earth results in a difference of approx.
		This implies, however, that not only the synodic lunar month of 29.53058867 days was known, but also the tropical month of 27.32158214 days, as well as the draconic month of 27.212221 days.
		By replacing the tropical lunar month of 27.32158214 days with the sidereal lunar month of 27.32166137 days, the result would be a Saros cycle of only 18.599260 years.
	siriusresearchgroup.com /articles/360-degree.shtml (928 words)

	Positional Astronomy: <br>Precession
		Around 2000 years ago, the Sun was in the constellation of Aries at the spring equinox, in Cancer at the summer solstice, Libra at the autumn equinox, and Capricorn at the winter solstice.
		The lunar contribution to luni-solar precession adds a short-period, small-amplitude wobble to the precessional movement of the North Celestial Pole, called nutation.
		This is planetary precession, which decreases the Right Ascension of every star by 0.13 arc-seconds per year, leaving the declination unchanged.
	www2.arnes.si /~gljsentvid10/sfera/chapt16.htm (561 words)

	ASTR 121, O'CONNELL. Study Guide 4 [Spring 2004]
		Though subtle, precession was first detected in 150 BC by Greek astronomer Hipparchus through comparison of measured star positions over several centuries.
		Precession causes changes in the N/S position of stars with respect to the poles/equator and therefore causes misalignments between ancient building sight lines and the current-day positions of stars.
		Precession shifts the location of intersections between the ecliptic and the equator (i.e.
	www.astro.virginia.edu /class/oconnell/astr121/guide04-s04.html (1600 words)

	Important Astronomers, their Instruments and Discoveries 1
		Aristarchus of Samos (250 BC?) calculated the distance of the Sun from the Earth and the Moon and Sun's sizes relative to Earth by observations during solar and lunar eclipses and at first quarter Moon using a Cross-staff.
		This remained the most precise calculation of equinoctal precession until it was redetermined at Samarkand by the Arabic astronomer Ulugh Begh in 1450.
		He measured the lunar orbit, determining lunar orbital precession and orbital eccentricity (125 BC?).
	obs.nineplanets.org /psc/hist1.html (940 words)

	W. B. Yeats and "A Vision": Astronomy
		The circles described by the Earth’s and the Celestial poles are centred on the Ecliptic poles, the Northern one situated in Draco and the Southern one in Doradus.
		The difference between these two Zodiacs is the effect of the precession (though the exact boundaries and date of coincidence are disputed), so that tropical Aries now starts at the same point as sidereal Pisces, and at midsummer, when the Sun is entering tropical Cancer, it is at the beginning of the constellation of Gemini.
		Within the Metonic cycle of 19 years the lunar calendar of synodic months reaches a form of accord with the solar calendar, so that the phases of the Moon occur on the same days of the solar year, though there is a slight difference and therefore a gradual accumulation of ‘error’.
	www.yeatsvision.com /Astronomy.html (2674 words)

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