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Orbit Of The Moon
The Moon
Moon
orbits Earth
Earth
in the prograde direction and completes one revolution relative to the stars in approximately 27.323 days (a sidereal month ) and one revolution relative to the Sun
Sun
in approximately 29.530 days (a synodic month ). Earth
Earth
and the Moon
Moon
orbit about their barycentre (common center of mass), which lies about 4,600 km (2,900 mi) from Earth's center (about 3/4 of the radius of Earth). On average, the distance to the Moon
Moon
is about 385,000 km (239,000 mi) from Earth's center, which corresponds to about 60 Earth
Earth
radii. With a mean orbital velocity of 1.022 km/s (2,290 mph), the Moon
Moon
appears to move relative to the stars each hour by an amount roughly equal to its angular diameter , or by about half a degree
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Obliquity
In astronomy , AXIAL TILT, also known as OBLIQUITY, is the angle between an object's rotational axis and its orbital axis, or, equivalently, the angle between its equatorial plane and orbital plane . It differs from orbital inclination . At an obliquity of zero, the two axes point in the same direction; i.e., the rotational axis is perpendicular to the orbital plane. Over the course of an orbit, the obliquity usually does not change considerably, and the orientation of the axis remains the same relative to the background stars . This causes one pole to be directed more toward the Sun
Sun
on one side of the orbit , and the other pole on the other side — the cause of the seasons on the Earth
Earth
. Earth's obliquity oscillates between 22.1 and 24.5 degrees on a 41,000-year cycle; the earth's mean obliquity is currently 23°26′13.2″ (or 23.43699°) and decreasing
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Axial Precession
In astronomy , AXIAL PRECESSION is a gravity-induced, slow, and continuous change in the orientation of an astronomical body's rotational axis . In particular, it can refer to the gradual shift in the orientation of Earth
Earth
's axis of rotation, which, similar to a wobbling top, traces out a pair of cones joined at their apices in a cycle of approximately 26,000 years. The term "precession" typically refers only to this largest part of the motion; other changes in the alignment of Earth's axis—nutation and polar motion —are much smaller in magnitude. Earth's precession was historically called the PRECESSION OF THE EQUINOXES, because the equinoxes moved westward along the ecliptic relative to the fixed stars , opposite to the yearly motion of the Sun along the ecliptic
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Jacques Cassini
JACQUES CASSINI (18 February 1677 – 16 April 1756) was a French astronomer , son of the famous Italian astronomer Giovanni Domenico Cassini . Cassini was born at the Paris Observatory . Admitted at the age of seventeen to membership of the French Academy of Sciences , he was elected in 1696 a fellow of the Royal Society
Royal Society
of London, and became maître des comptes in 1706. Having succeeded to his father's position at the observatory in 1712, he measured in 1713 the arc of the meridian from Dunkirk
Dunkirk
to Perpignan
Perpignan
, and published the results in a volume entitled Traité de la grandeur et de la figure de la terre (1720). His two separate calculations for a degree of meridian arc were 57,097 toises de Paris (111.282 km) and 57,061 toises (111.211 km), giving results for Earth's radius of 3,271,420 toises (6,375.998 km) and 3,269,297 toises (6,371.860 km), respectively
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Cassini's Laws
CASSINI\'S LAWS provide a compact description of the motion of the Moon
Moon
. They were established in 1693 by Giovanni Domenico Cassini
Giovanni Domenico Cassini
, a prominent scientist of his time. Refinements of these laws to include physical librations have been made, and they have been generalized to treat other satellites and planets. CONTENTS * 1 Cassini\'s laws * 2 Cassini state * 3 References and notes * 4 Further reading * 5 See also CASSINI\'S LAWS Orbital inclination and rotation. * The Moon
Moon
has a 1:1 spin–orbit resonance . This means that the rotation –orbit ratio of the Moon
Moon
is such that the same side of it always faces the Earth
Earth
. * The Moon's rotational axis maintains a constant angle of inclination from the ecliptic plane
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North Pole
Coordinates : 90°N 0°W / 90°N -0°E / 90; -0 An azimuthal projection showing the Arctic Ocean and the North Pole. The map also shows the 75th parallel north and 60th parallel north . North Pole scenery The NORTH POLE, also known as the GEOGRAPHIC NORTH POLE or TERRESTRIAL NORTH POLE, is (subject to the caveats explained below) defined as the point in the Northern Hemisphere where the Earth\'s axis of rotation meets its surface. The North Pole is the northernmost point on the Earth, lying diametrically opposite the South Pole . It defines geodetic latitude 90° North, as well as the direction of true north . At the North Pole all directions point south; all lines of longitude converge there, so its longitude can be defined as any degree value. Along tight latitude circles, counterclockwise is east and clockwise is west
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Major Axis
In geometry , the MAJOR AXIS of an ellipse is its longest diameter : a line segment that runs through the center and both foci , with ends at the widest points of the perimeter . The SEMI-MAJOR AXIS is one half of the major axis, and thus runs from the centre, through a focus , and to the perimeter. Essentially, it is the radius of an orbit at the orbit's two most distant points. For the special case of a circle, the semi-major axis is the radius . One can think of the semi-major axis as an ellipse's long radius. The length of the semi-major axis a {displaystyle a} of an ellipse is related to the semi-minor axis 's length b {displaystyle b} through the eccentricity e {displaystyle e} and the semi-latus rectum {displaystyle ell } , as follows: b = a 1 e 2 , = a ( 1 e 2 ) , a = b 2
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Orbital Inclination
ORBITAL INCLINATION measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a reference plane and the orbital plane or axis of direction of the orbiting object. For a satellite orbiting the Earth directly above the equator, the plane of the satellite's orbit is the same as the Earth's equatorial plane, and the satellite's orbital inclination is 0°. The general case is that the satellite's orbit is tilted; it spends half an orbit over the northern hemisphere and half over the southern. If the orbit swung between 20° north latitude and 20° south latitude, then its orbital inclination would be 20°. CONTENTS* 1 Orbits * 1.1 Natural and artificial satellites * 1.2 Exoplanets and multiple star systems * 2 Other meaning * 3 Calculation * 4 See also * 5 References ORBITSThe inclination is one of the six orbital elements describing the shape and orientation of a celestial orbit
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Opposition (astronomy)
In positional astronomy , two astronomical objects are said to be in OPPOSITION when they are on opposite sides of the celestial sphere , as observed from a given body (usually Earth
Earth
). A planet (or asteroid or comet ) is said to be "in opposition" when it is in opposition to the Sun
Sun
. Because most orbits in the Solar System are nearly coplanar to the ecliptic , this occurs when the Sun , Earth
Earth
, and the body are configured in an approximately straight line, or syzygy ; that is, Earth
Earth
and the body are in the same direction as seen from the Sun. Opposition occurs only for superior planets (see the diagram). The instant of opposition is defined as that when the apparent geocentric celestial longitude of the body differs by 180° from the apparent geocentric longitude of the Sun
Sun

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Syzygy (astronomy)
In astronomy , a SYZYGY (/ˈsɪzɪdʒi/ ; from the Ancient Greek σύζυγος suzugos meaning, "yoked together" ) is a straight-line configuration of three celestial bodies in a gravitational system. Mercury transiting the Sun
Sun
as viewed by the Curiosity rover on Mars (June 3, 2014). CONTENTS * 1 Overview * 2 Occultations, transits, and eclipses * 3 Tidal variation * 4 References OVERVIEWThe word is often used in reference to the Sun
Sun
, Earth
Earth
, and either the Moon
Moon
or a planet , where the latter is in conjunction or opposition . Solar and lunar eclipses occur at times of syzygy, as do transits and occultations . The term is often applied when the Sun
Sun
and Moon
Moon
are in conjunction (new moon ) or opposition (full moon ). The word syzygy is often loosely used to describe interesting configurations of planets in general
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Quadrature (astronomy)
In spherical astronomy , QUADRATURE is the configuration of a celestial object in which its elongation is perpendicular to the direction of the Sun
Sun
. It is applied especially to the position of a superior planet or the Moon
Moon
at its first and last quarter phases . As shown in the diagram above, a planet (or other object) can be at the western quadrature (when it is to the west of the Sun
Sun
when viewed from the Earth) or at the eastern quadrature (when it is to the east of the Sun
Sun
when viewed from the Earth). Note that an inferior planet can never be at quadrature to the reference planet. Since the Sun is not infinitely far away, the Moon
Moon
is slightly past first quarter phase when the Sun
Sun
and Moon
Moon
are perpendicular in the sky to each other
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Apsidal Precession
In celestial mechanics , APSIDAL PRECESSION or ORBITAL PRECESSION is the precession (rotation) of the orbit of a celestial body . More precisely, it is the gradual rotation of the line joining the apsides of an orbit, which are the points of closest and farthest approach. Perihelion is the closest point to the Sun
Sun
. The apsidal precession is the first derivative of the argument of periapsis , one of the six primary orbital elements of an orbit. CONTENTS * 1 History * 2 Calculation * 3 Newton\'s theorem of revolving orbits * 4 General relativity
General relativity
* 5 Long-term climate * 6 See also * 7 Notes HISTORYThe ancient Greek astronomer Hipparchos
Hipparchos
noted the apsidal precession of the Moon's orbit; it is corrected for in the Antikythera Mechanism (circa 80 BCE) with the almost exactly accurate value of 8.88 years per full cycle, correct within 0.34%
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South Pole
Coordinates : 90°S 180°E / 90°S 180°E / -90; 180 * South Geographic Pole * South Magnetic Pole (2007) * South Geomagnetic Pole (2005) * South Pole of Inaccessibility The SOUTH POLE, also known as the GEOGRAPHIC SOUTH POLE or TERRESTRIAL SOUTH POLE, is one of the two points where the Earth\'s axis of rotation intersects its surface. It is the southernmost point on the surface of the Earth and lies on the opposite side of the Earth from the North Pole
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Winter Solstice
The WINTER SOLSTICE (or HIBERNAL SOLSTICE), also known as MIDWINTER, is an astronomical phenomenon marking the day with the shortest period of daylight and the longest night of the year. In the Northern Hemisphere this is the December solstice and in the Southern Hemisphere this is the June solstice . The axial tilt of Earth and gyroscopic effects of its daily rotation mean that the two opposite points in the sky to which the Earth's axis of rotation points (axial precession ) change very slowly (making a complete circle approximately every 26,000 years). As the Earth follows its orbit around the Sun, the polar hemisphere that faced away from the Sun, experiencing winter, will, in half a year, face towards the Sun and experience summer. This is because the two hemispheres face opposite directions along Earth's axis, and so as one polar hemisphere experiences winter , the other experiences summer
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Scale Model
A SCALE MODEL is most generally a physical representation of an object, which maintains accurate relationships between all important aspects of the model, although absolute values of the original properties need not be preserved. This enables it to demonstrate some behavior or property of the original object without examining the original object itself. The most familiar scale models represent the physical appearance of an object in miniature, but there are many other kinds. Scale models are used in many fields including engineering, architecture, film making, military command, salesmanship and hobby model building. While each field may use a scale model for a different purpose, all scale models are based on the same principles and must meet the same general requirements to be functional. The detail requirements vary depending on the needs of the modeler
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Sunrise
SUNRISE or SUN UP is the instant at which the upper edge of the Sun appears over the horizon in the morning . The term can also refer to the entire process of the Sun
Sun
crossing the horizon and its accompanying atmospheric effects. CONTENTS* 1 Terminology * 1.1 "Rise" * 1.2 Beginning and end * 2 Measurement * 2.1 Angle * 2.2 Time of day * 2.3 Location on the horizon * 3 Appearance * 3.1 Colors * 3.2 Optical illusions and other phenomena * 4 See also * 5 References * 6 External links TERMINOLOGY"RISE"Although the Sun
Sun
appears to "rise" from the horizon, it is actually the _Earth's_ motion that causes the Sun
Sun
to appear
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