Obliquity of the ecliptic for 20, 000 years, from Laskar ( 1986 ).

Obliquity of the ecliptic for 20, 000 years, from Laskar ( 1986 ).

Obliquity of the ecliptic for the past 5 million years, from Berger ( 1976 ).

Obliquity of the ecliptic for the next 1 million years, from Berger ( 1976 ).

Obliquity: Why our goals are best achieved indirectly is a book by economist John Kay.

His observations on eclipses were still used centuries later in Simon Newcomb's investigations on the motion of the moon, while his other observations inspired Laplace's Obliquity of the Ecliptic and Inequalities of Jupiter and Saturn.

* 1999 " Mars Secular Obliquity Change Due to Water Ice Caps ," J. Geophys.

* 1993 " The Obliquity of Mars and " Climate Friction ," J. Geophys.

Also, planetary gravitational attraction increases the dust concentration near the plane of the ecliptic as the sun is approached.

Western astrology is founded on the movements and relative positions of celestial bodies such as the Sun, Moon, planets, which are analyzed by their movement through signs of the zodiac ( spatial divisions of the ecliptic ) and by their aspects ( angles ) relative to one another.

) Along with Aldebaran, Spica, and Regulus it is one of the four brightest stars near the ecliptic.

In classical Chinese astronomy, the northern sky is divided geometrically, into five " enclosures " and twenty-eight mansions along the ecliptic, grouped into Four Symbols of seven asterisms each.

Although Cetus is not generally considered part of the zodiac, the ecliptic passes close to its constellation boundary, and thus the planets may be seen in Cetus for brief periods of time.

This is even more true of asteroids, since their orbits usually have a greater inclination to the ecliptic than planets.

The primary direction of the system is the equinox | vernal equinox, the ascending node of the ecliptic ( red ) on the celestial equator ( blue ).

The ecliptic is the path the Sun appears to trace through the stars.

The ecliptic is the apparent path of the Sun on the celestial sphere as seen from the Earth's center, and also the plane of this path, which is coplanar with the orbit of the Earth around the Sun.

The ecliptic is actually the apparent path of the Sun throughout the course of a year.

Also, the Earth does not actually orbit the Sun, but the Solar System barycenter, therefore an alternate definition of the ecliptic is the mean plane of the orbit of Earth-Moon barycenter around the Solar System barycenter.

As the rotational axis of the Earth is not perpendicular to its orbital plane, the Earth's equatorial plane is not coplanar with the ecliptic plane, but is inclined to it by an angle of about 23 °. 4, which is known as the obliquity of the ecliptic.

If the equator is projected outward to the celestial sphere, forming the celestial equator, it crosses the ecliptic at two points known as the equinoxes.

The crossing from south to north is known as the vernal equinox, also known as the first point of Aries and the ascending node of the ecliptic on the celestial equator.

The orientation of the Earth's axis and equator are not fixed in space, but rotate about the poles of the ecliptic with a period of about 26, 000 years, a process known as lunisolar precession, as it is due mostly to the gravitational effect of the Moon and Sun on the Earth's equatorial bulge.

Likewise, the ecliptic itself is not fixed.

What follows is a list of the twelve signs of the modern zodiac ( with the ecliptic longitudes of their first points ), where 0 ° Aries is understood as the vernal equinox, with their Latin, Greek, Sanskrit, and Babylonian names ( but note that the Sanskrit and the Babylonian name equivalents denote the constellations only, not the tropical zodiac signs ).

The Babylonian star catalogues name them MUL. MUL or " star of stars ", and they head the list of stars along the ecliptic, reflecting the fact that they were close to the point of vernal equinox around the 23rd century BC.

The name of this device comes ultimately from the Latin armilla ( circle, bracelet ), since it has a skeleton made of graduated metal circles linking the poles and representing the equator, the ecliptic, meridians and parallels.

The Lüshi Chunqiu written by the Qin statesman Lü Buwei ( d. 235 BC ) provides most of the names for the twenty-eight mansions ( i. e. asterisms across the ecliptic belt of the celestial sphere used for constructing the calendar ).

The term heliacal circle is used for the ecliptic, which is in the center of the zodiacal circle, conceived as a band including the noted constellations named on mythical themes.

The ecliptic coordinate system is a celestial coordinate system commonly used for representing the positions and orbits of Solar System objects.

Eratosthenes most probably used a solstitial armilla for measuring the obliquity of the ecliptic.

Celestial coordinate systems most commonly used in astronomy are equatorial coordinates and ecliptic coordinates.

Thus the coordinate systems most used in astronomy need their own date-reference because the coordinate systems of that type are themselves in motion, e. g. by the precession of the equinoxes, nowadays often resolved into precessional components, separate precessions of the equator and of the ecliptic.

( Sometimes the word ' equinox ' may be used alone, e. g. where it is obvious from the context to users of the data in which form the considered astronomical variables are expressed, in equatorial form or ecliptic form.

The equinox with equator / ecliptic of a given date defines which coordinate system is used.

Thus a particular coordinate system ( equinox and equator / ecliptic of a particular date, such as J2000. 0 ) could be used forever, but a set of osculating elements for a particular epoch may only be ( approximately ) valid for a rather limited time, because osculating elements such as those exampled above do not show the effect of future perturbations which will change the values of the elements.

Jumps are normally made to and from points far above a solar system's ecliptic, usually where the gravitational influence in the system is most stable ; however, so-called " pirate points " exist where local gravitational pull is stable enough to used ; though quicker, using such points is also more dangerous due the random appearance of so-called " Lagrange points ".

They are also used as terms for two systems of ecliptic coordinates used in astrology.

For the purpose of determining the constellations in contact with the ecliptic, the constellation boundaries as defined by the International Astronomical Union in 1930 are used.

The ROSAT spacecraft was a three-axis stabilized satellite which can be used for pointed observations, for slewing between targets, and for performing scanning observations on great circles perpendicular to the plane of the ecliptic.

The points are spaced 15 ° apart along the ecliptic and are used by lunisolar calendars to stay synchronized with the seasons, which is crucial for agrarian societies.

Guo used a quadrangular spherical pyramid, the basal quadrilateral of which consisted of one equatorial and one ecliptic arc, together with two meridian arcs, one of which passed through the summer solstice point ... By such methods he was able to obtain the du lü ( degrees of equator corresponding to degrees of ecliptic ), the ji cha ( values of chords for given ecliptic arcs ), and the cha lü ( difference between chords of arcs differing by 1 degree ).

Geometrical principles are used to define the favourable or unfavourable quality of astrological aspects, based on the angular relationship of planets and signs with ecliptic degrees.