Solstice | Define Solstice at Dictionary.com solstice [sol-stis, sohl-] /ˈsɒl stɪs, ˈsoʊl-/ Spell 1. Astronomy. either of the two times a year when the sun is at its greatest distance from the celestial equator: about June 21, when the sun reaches its northernmost point on the celestial sphere, or about December 22, when it reaches its southernmost point. either of the two points in the ecliptic farthest from the equator. 2. a furthest or culminating point; a turning point. Origin of solstice Latin 1200-1250 1200-50; < Middle English < Old French < Latin sōlstitium, equivalent to sōl sun + -stit-, combining form of stat-, variant stem of sistere to make stand (see stand ) + -ium -ium ; see -ice ) Dictionary.com Unabridged Examples from the Web for solstice Expand Contemporary Examples The darkest day comes on the Winter solstice (December 21), when a full moon eclipse will wreak its own special havoc. A Speckled Bird Augusta J.

Evans Wilson At the summer solstice, he offers sacrifices to the earth; at the winter solstice, to heaven. British Dictionary definitions for solstice Expand noun 1. either the shortest day of the year (winter solstice) or the longest day of the year (summer solstice) 2. either of the two points on the ecliptic at which the sun is overhead at the tropic of Cancer or Capricorn at the summer and winter solstices Derived Forms solstitial (sɒlˈstɪʃəl) adjective Word Origin C13: via Old French from Latin sōlstitium, literally: the (apparent) standing still of the sun, from sōl sun + sistere to stand still Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012 Word Origin and History for solstice Expand n.

mid-13c., from Old French solstice (13c.), from Latin solstitium "point at which the sun seems to stand still," especially the summer solstice, from sol "sun" (see sol ) + past participle stem of sistere "to come to a stop, make stand still" (see assist (v.)). Online Etymology Dictionary, © 2010 Douglas Harper solstice (sŏl'stĭs, sōl'-) Either of the two points on the celestial sphere where the ecliptic (the apparent path of the Sun) reaches its greatest distance north or south of the celestial equator. ◇ The northernmost point of the Sun's path, called the summer solstice, lies on the Tropic of Cancer at 23°27' north latitude. ◇ The southernmost point of the Sun's path, called the winter solstice, lies on the Tropic of Capricorn at 23°27' south latitude. Either of the two corresponding moments of the year when the Sun is directly above either the Tropic of Cancer or the Tropic of Capricorn.

The summer solstice occurs on June 20 or 21 and the winter solstice on December 21 or 22, marking the beginning of summer and winter in the Northern Hemisphere (and the reverse in the Southern Hemisphere). The days on which a solstice falls have the greatest difference of the year between the hours of daylight and darkness, with the most daylight hours at the beginning of summer and the most darkness at the beginning of winter. Compare equinox . The American Heritage® Science Dictionary Copyright © 2002. Published by Houghton Mifflin. All rights reserved. Expand solstice [(sol-stuhs, sohl-stuhs)] The two occasions each year when the position of the sun at a given time of day does not seem to change direction. In the Northern Hemisphere , the summer solstice occurs around June 21 and is the longest day of the year. The sun stops getting higher in the sky, and the days begin to grow shorter. The winter solstice, which occurs around December 21, is the shortest day. The sun stops getting lower in the sky, and the days begin to grow longer.

The American Heritage® New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved. Ecliptic peak - definition of Ecliptic peak by The Free Dictionary Ecliptic peak - definition of Ecliptic peak by The Free Dictionary Also found in: Thesaurus , Encyclopedia , Wikipedia . sol·stice (sōl′stĭs, sŏl′-, sôl′-) n. Either of two times of the year when the sun is at its greatest angular distance from the celestial equator. The summer solstice in the Northern Hemisphere occurs about June 21, when the sun is at the zenith on the Tropic of Cancer; the winter solstice occurs about December 21, when the sun is at zenith on the Tropic of Capricorn. The summer solstice is the longest day of the year; the winter solstice is the shortest.

[Middle English, from Old French, from Latin sōlstitium : sōl, sun; see sāwel- in the Appendix of Indo-European roots + -stitium, a stoppage; see stā- in the Appendix of Indo-European roots.] sol·sti′tial (-stĭsh′əl) adj. solstice (ˈsɒlstɪs) n 1. (Astronomy) either the shortest day of the year (winter solstice) or the longest day of the year (summer solstice) 2. (Physical Geography) either of the two points on the ecliptic at which the sun is overhead at the tropic of Cancer or Capricorn at the summer and winter solstices [C13: via Old French from Latin sōlstitium, literally: the (apparent) standing still of the sun, from sōl sun + sistere to stand still] solstitial adj n. 1. a. either of the two times a year when the sun is at its greatest distance from the celestial equator: about June 21, when the sun reaches its northernmost point on the celestial sphere, or about Dec.

22, when it reaches its southernmost point. b. either of the two points in the ecliptic farthest from the equator. 2. a furthest point. [1200–50; < Middle English < Old French < Latin sōlstitium=sōl sun + -stit-, derivative of sistere to make stand; see stand ] sol·stice (sŏl′stĭs, sōl′stĭs) 1. Either of the two moments of the year when the sun is farthest north or south of the celestial equator. In the Northern Hemisphere, the summer solstice occurs on June 20 or 21 and the winter solstice occurs on December 21 or 22. 2. Either of the two points on the celestial sphere where the apparent path of the sun (known as the ecliptic) reaches its greatest distance from the celestial equator. Compare equinox . solstice - Derived from the Latin sol, "Sun," and stitium, "stoppage," as the Sun appears to stand still on the first day of winter. See also related terms for stoppage .

ThesaurusAntonymsRelated WordsSynonymsLegend: Matrix Astrology Software : Learn Astrology - Visual Astrology - Ecliptic Coordinate System Click here to go back to Visual Astrology Ecliptic Coordinate System Ecliptic Coordinates -- In this system, the ecliptic or plane through the Earth's orbit is taken as the plane of reference. The co-ordinates used are Celestial Latitude (the perpendicular distance of the object from the ecliptic in angular measure) and Celestial Longitude (the angular distance along the ecliptic between the plane through the object and the First Point of Aries). The Solstitial Colure is the great circle which passes through the summer and winter solstices (the hour circle of R.A. 90� and 270�). Ecliptic Sphere -- Also called the Zodiac Sphere, this is the sphere resulting from projecting the plane of the Earth's orbit and points (its poles) 90� north and south of that plane. Ecliptic Plane -- The ecliptic is a plane that passes through the centers of the Earth and the Sun.

It represents the path the Sun's center takes each year on the celestial sphere as seen from the Earth or the Earth's path as seen around the Sun. North Ecliptic Pole -- The point on the ecliptic sphere that are 90 degrees from the plane of the ecliptic, to the North or 'above'. NEP -- North Ecliptic Pole South Ecliptic Pole -- The point on the ecliptic sphere that are 90 degrees from the plane of the ecliptic, to the South or 'below'. SEP -- South Ecliptic Pole Obliquity of the Ecliptic -- The 23 1/2� angle (23�27') that represents the inclination of the ecliptic to the celestial equator. This also marks the maximum angular distance that the Sun can reach north or south of the celestial equator at the times of the solstices. Celestial Latitude (Ecliptic Latitude) -- The angular distance of any object measured north or south of the plane of the ecliptic to the poles, from 0� to 90�.

Celestial Longitude (Ecliptic Longitude) -- The angular distance of any object as measured from zero Aries to a plane through an object. Zodiac -- From a Greek word meaning the 'circle of animals', is a belt about 18� wide (9� above and 9� below the plane of the ecliptic) within which the planets travel. This circle is divided into 12 equal 30� sections, the signs of the zodiac -- Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius, and Pisces. At one point (over 2000 years ago), the signs of the zodiac corresponded with the constellations of the same name. However, due to precession, the signs have drifted westward (backward) until today they are almost an entire sign (30�) off. Solstices -- The longest and shortest days of the year, when the Sun reaches its greatest angular distance from the equator. The longest day is the summer solstice (around June 21) and the shortest day is the winter solstice (around December 22).

These two are reversed in the southern hemisphere. Solstice Points -- The instant when the Sun is at either the summer or winter solstice. Equinoxes (Spring and Fall) -- This is the instant when Sun crosses the celestial equator at either its ascending node (Spring Equinox, about March 21) or its descending node (Fall Equinox, September 23). At the Spring Equinox, the Sun moves north of the ecliptic plane, while at the fall Equinox, it moves from north to south. Spring Equinox (Vernal Equinox) Fall Equinox (Autumnal Equinox) Zero Aries -- The intersection of the celestial equator and the ecliptic. This point undergoes a very slow backward movement. Colures -- There are two, the equinoctial colure and the solstitial colure. The equinoctial colure is the hour circle that passes through the vernal and autumnal equinoctial points (RA 0h and 12 h).

The solstitial colure is the hour circle that passes through the summer and winter solstices (0� points of the tropical zodiac signs Cancer and Capricorn at RA 6h and 18h). Copyright (c) 1997 Michael Erlewine HW3c.questions - How are these four points related to the ecliptic and the HW3c.questions HW3c.questions - How are these four points related to the... SCHOOL View Full Document HW Week #3C – Six Problems from the book Chapter 2: Problems: 14, 15, 16, 18, 19, 20 14. Give two reasons why it is warmer in summer than in winter. Because of the tilt of the earth, there are more hours of sunlight in the summer, and the sunrays hit more directly. 15. What is the ecliptic plane? What is the ecliptic? The ecliptic plane is the plane of Earth’s orbit around the sun. The ecliptic is the path of the sun across the celestial sphere over an entire year. 16. Why is the ecliptic tilted with respect to the celestial equator?

Does the Sun appear to move along the ecliptic, the celestial equator, or neither? By about how many degrees does the Sun appear to move on the celestial sphere each day? Because the earth itself is tilted 23.5 degrees, the ecliptic is tilted 23.5 degrees from the celestial equator. The Sun appears to move along the ecliptic. The Sun appears to move about 1 degree per day on the celestial sphere. 18. What are the vernal and autumnal equinoxes? What are the summer and winter solstices? This is the end of the preview. Sign up to access the rest of the document. Unformatted text preview: How are these four points related to the ecliptic and the celestial equator? The autumnal equinox is the intersection of the ecliptic and celestial equator where the Sun crosses the equator from north to south. The vernal equinox is the point on the ecliptic where the Sun crosses the celestial equator from south to north. The summer solstice is the point on the ecliptic where the Sun is farthest north of the celestial equator.

The winter solstice is the point on the ecliptic where the Sun reaches its greatest distance south of the celestial equator. 19. At what point on the horizon does the vernal equinox rise? Where on the horizon does it set? (Hint: See Figure 2-16.) It rises due east and sets due west. 20. How does the daily path of the Sun across the sky change with the seasons? Why does it change? When the sun sets, it moves slightly north from Dec 21 to June 21 and moves south from June 21 to Dec 21. It changes because of the tilt of the earth.... Astronomy Ranking Task: The Seasons Exercise #1 Description: T hefigurebelowshowstheE H The Basics – The Ecliptic, The Equator And Coordinate Systems - Astrology Club The Basics – The Ecliptic, The Equator And Coordinate Systems The Ecliptic System and the Zodiac The term ecliptic is mentioned often in astrology. It describes the centerline of that which we call the Zodiac, which extends some eight degrees above and below the ecliptic.

In other words, the Zodiac is a belt 16° wide centered on the ecliptic. But what defines the ecliptic? Simply put, the ecliptic is the plane of the Earth’s orbit around the Sun. A plane is merely a flat two-dimensional surface (it has length and width, but no depth). The Earth’s orbit, viewed from the side (like a circle viewed from the side), is a plane. So the ecliptic is the circle (plane) of the Earth’s orbit extended to infinity. Since we live on the Earth, and not on the Sun, we seem to see the Sun moving along the ecliptic rather than the Earth. As we pear into the heavens, the Sun appears to follow its endlessly cyclic path through the center of the Zodiac. What’s actually happening is that we’re following our endlessly cyclic path around the Sun, and we’re in the opposite sign (at least, we are from the Sun’s point of view). Nevertheless, we live HERE, on the Earth, so it’s only natural that HERE becomes the center of our point of view, our psyches, and our astrological system.

It takes the Earth about 3651/4 days to complete its journey around the Sun – consequently, it takes the Sun 3651/4 days to complete its apparent journey around the Earth. This cycle defines our astronomical year. It also comprises our calendar year. Due to that extra 1/4 day that it takes the Earth to complete its journey, our calendar of 365 days is corrected once every four years with an extra day added to February (since 1/4 day/year X 4 years = 1 day). We call this Leap Year. Whenever I’ve seen a documentary style show on astrology, a scientist (or scientists), is always interviewed on the subject. Naturally, they always point out that “it can’t possibly work” because it’s a system based upon an Earth-centered solar system, where everything revolves around the Earth. They continue that, although we once believed this to be the case, we now know that the Sun is the center of the solar system, so astrology can’t possibly work because its fundamental assumption is irreparably flawed.

I always have to smile when I hear this, since these same scientists use coordinate systems for locating the stars which are also Earth-based, or Earth-centered (usually the Equatorial System which uses Right Ascension and Declination to define coordinates 2 ). Does this mean that the sciences of astronomy and cosmology can’t possibly be right either? Somehow, this question is never asked. The position of a heavenly body is measured in the Ecliptic System using Celestial Longitude and Celestial Latitude. Celestial Longitude is measured horizontally starting at 0° of Aries 1. Position is measured in degrees, minutes, and seconds of arc in a counter-clockwise direction along the Ecliptic. For example, a planet located at 15° of Taurus could also be said to be located at 45° of Celestial Longitude (the 30° of Aries + the 15° into Taurus). Having located a body horizontally in Celestial Longitude, we still need to describe its position vertically in order to pinpoint its precise location. In the Ecliptic System, this is done using Celestial Latitude.

A body’s position is again expressed in degrees, minutes, and seconds of arc, but this time with reference to its distance above or below the plane of the Ecliptic. This is exactly the same as describing latitude on the surface of the Earth, except we use the Ecliptic in place of the Earth’s Equator. A body above the Ecliptic is expressed as North Celestial Latitude, just as a position on Earth’s surface above the Equator is said to be North latitude. Similarly, a body below the Ecliptic is expressed as South Celestial Latitude. While Celestial Longitude is used extensively in astrology, Celestial Latitude is not as frequently employed. Instead, astrologers use Declination. The Equatorial System Almost everyone has heard of the Equator. It is a circle that bands the sphere of the Earth at it’s thickest point, defining 0° of terrestrial latitude and separating the northern hemisphere from the southern hemisphere. The Equator is perpendicular to the Earth’s Axis of Rotation. The Earth spins on its Axis of Rotation once a day, with this Axis tilted 661/2° with respect to the Ecliptic.

As a result, the Equator is tilted 231/2° with respect to the Ecliptic. Since the Equator is a circle, it too is a plane which is perpendicular to the Axis of Rotation, and which passes through the center of the Earth. When we extend this plane out into space, it becomes the Celestial Equator, which is, again, tiled with respect to the Ecliptic by an angle of 231/2°. So why should we, as astrologers, care? As was said before, astrologers measure horizontal positions of the planets and other heavenly bodies using Celestial Longitude. However, we don’t measure vertical position in Celestial Latitude. Instead, we use something called Declination. Declination is the distance of a body, in degrees, minutes, and seconds of arc, above or below the Celestial Equator (not above or below the Ecliptic as is the case with Celestial Latitude). The Parallel and Contra-Parallel Aspects are aspects of Declination. In the first case, two or more planets or bodies share the same Declination – i.e. both being at the same degree of Declination either North or South.

In the second case, two bodies share the same degree of Declination, but ONE is North and ONE is SOUTH! The Equator, the Ecliptic, and the Seasons The tilt of the Earth’s Axis of Rotation is also responsible for our seasons. This is reflected in the yearly cycle of the Sun’s Declination. The Sun is always at 0° of Celestial Latitude, since it is always right on the Ecliptic. However, throughout the yearly cycle as the Earth travels around the Sun, the Earth’s Axis of Rotation will be tilted either towards the Sun, away from the Sun, or somewhere in between. In the illustration below, note that the Celestial Equator intersects the Ecliptic at two points. These points define a line which precisely pass through 0° Aries and 0° Libra. It is precisely this intersection which defines the Vernal Equinox and the Autumnal Equinox, and the first degree of both Aries and Libra (speaking of the Tropical Zodiac).

At the Vernal Equinox, which is the beginning of spring, and also defines 0° Aries (at least in the Tropical Zodiac), the Earth’s Axis of Rotation is perpendicular to the Sun, and perpendicular to the Line of Intersection between the Ecliptic and the Celestial Equator. The days and nights all over the globe are of equal length (the word equinox is derived from the medieval Latin aequus, meaning equal, and nox meaning night).The Sun’s Declination is 0°, since the Sun is also aligned with the Line of Intersection. Three months (and 90° of orbit), later, we have the Summer Solstice. At this point, the Earth’s Axis of Rotation is tilted towards the Sun, and is aligned with the Line of Intersection. Since the Northern Hemisphere is tilted towards the Sun, this is the longest day of the year. The Sun’s rays strike us at less of an angle, temperatures are consequently warmer, and we have Summer in the Northern Hemisphere, while the Southern Hemisphere, experiencing the exact opposite orientation, has its Winter.

Again, due to the Northern Hemisphere being tilted as much towards the Sun as it’s going to, the Sun reaches maximum Northern Declination in the sky – exactly 231/2° North Declination. It is this which defines the Tropic of Cancer, another belt which girdles the Earth exactly 231/2° above the Equator. Also note that the Arctic Circle, which lies at 661/2° terrestrial latitude, just touches, or is tangent to, the terminator (the line separating Earth’s day-side from its night-side). It is this point of tangency which in fact defines the Arctic and Antarctic Circles. On the Arctic Circle at the Summer Solstice, the Sun will never completely set, and will just touch the horizon before beginning to climb back into the sky again. At and above this latitude, the Sun never sets in the summer. The opposite is of course true at or below the Antarctic Circle, where 24 hours of night reigns. After another three months (and another 90° of orbit), we have the Autumnal Equinox. Again, the Earth’s Axis of Rotation is perpendicular to the Sun, and perpendicular to the Line of Intersection.

The days and nights are again of equal length, and the Sun’s Declination is again 0°. The last of the seasons is Winter, which happens three months (and 90° of orbit), after the Autumnal Equinox. At this point in its orbit, the Earth’s Axis of Rotation is tilted as far away from the Sun as it will get (so far as the Northern Hemisphere is concerned). This is the shortest day of the year. The Sun’s rays strike us at their greatest oblique angle, temperatures are consequently colder, and we have Winter in the Northern Hemisphere. Again, the Southern Hemisphere experiences the exact opposite orientation, and has its Summer. The Sun reaches maximum Southern Declination in the sky – exactly 231/2° South Declination. It is this which defines the Tropic of Capricorn, a third belt which circles the Earth exactly 231/2° below the Equator. The Antarctic circle and latitudes below are bathed in 24 hours of daylight, while the Arctic Circle and points above are having 24 hours of night.

Long and Short Days While not necessarily of use to the astrologer, it is nonetheless interesting to look at the reason for the varying length of the day throughout the year. This can be most clearly illustrated with another illustration. For simplicity, the above picture assumes one is located exactly on the Tropic of Cancer at 231/2° north latitude. As can be seen, the angle of the Earth’s surface contained within the daylight side varies with the time of year from 201.8° at the Summer Solstice to 158.2° at the Winter Solstice. Since the Earth rotates one full revolution, or 360° every 24 hours, we can calculate that it rotates 360/24=15° each hour. So, at the Summer Solstice, the longest day of the year, we have 201.8° of daylight, or 201.8°/15° per hour = 13.45 hours = 13 hours 27 minutes of daylight. At the Winter Solstice, the shortest day of the year, the angle of daylight is only 158.2°.

In this case, we have 158.2°/15° per hour = 10.55 hours = 10 hours 33 minutes of daylight. Lastly, we know the Equinox is supposed to contain equal hours of day and night, or 12 hours each. We see above that the angle of daylight is 180° – exactly half of 360°. We can see right away that the length of daylight equals the length of night, but if we want to do the proof, we have 180°/15° per hour = 12 hours of daylight. Notes: 1 0° of Aries is defined in the Tropical Zodiac by the point of the Vernal Equinox, or that point where the Sun has 0° of Declination as it moves north after the Winter Solstice. The Sidereal Zodiac, however, is a system based upon the constellations themselves, and defines 0° Aries by a different system.

Due to the Procession of the Equinoxes, these two zodiacs have, at this point in time, diverged almost a full sign, so that what is in Aries in the Tropical Zodiac is in Pisces in the Sidereal Zodiac. The astronomical phenomenon responsible for the Procession of the Equinoxes, and for the Great Ages, of which the “Age of Aquarius” is one, will be the subject of a future article. 2 While we, as astrologers, use Celestial Longitude divided into the Zodiac to define horizontal coordinates, astronomers generally use Right Ascension. As with Celestial Latitude, measurement begins with 0° corresponding to the point of the Vernal Equinox. However, where Celestial Latitude measures counter-clockwise, Right Ascension measures clockwise from this point, with the measurement being expressed either in degrees, minutes, and seconds of arc, or in hours, minutes, and seconds of time. In any event, it is still a system which used the Earth as its center of reference. Why that’s logical and okay for astronomical measurement, but irrational and not okay for astrological measurement is beyond me! About the author: Dwight Ennis has studied astrology for more than 20 years.

He was one of the founding members of the South Bay Astrological Society, and was its first President, serving two terms. His primary astrological focus is on the blending of astrological symbolism with Jungian Depth Psychology. Orbits and the Ecliptic Plane Ecliptic Plane If the sun's path is observed from the Earth's reference frame, it appears to move around the Earth in a path which is tilted with respect to the spin axis at 23.5°. This path is called the ecliptic . It tells us that the Earth's spin axis is tilted with respect to the plane of the Earth's solar orbit by 23.5°. Observations show that the other planets, with the exception of Pluto , also orbit the sun in essentially the same plane. The ecliptic plane then contains most of the objects which are orbiting the sun. This suggests that the formation process of the solar system resulted in a disk of material out of which formed the sun and the planets. The 23.5° tilt of the Earth's spin axis gives the seasonal variations in the amount of sunlight received at the surface.

Pluto 's orbit is exceptional in that its orbit makes an angle of 17° with the Earth's orbit. This has led to a number of theories about Pluto's origin. Mercury is the only other planet which moves significantly away from the ecliptic plane ( 7°) . Go Back Declination and Right Ascension Right ascension and declination are like longitude and latitude on the surface of the Earth except that they are measured with respect to the celestial sphere with the vernal equinox as the origin. The right ascension and declination for a celestial object constitute a unique designation of its position, and from them one can determine the observer coordinates necessary to find the object in their frame of reference. Right ascension is a celestial longitude measured in the direction of the Earth's rotation. Since that rotation makes a complete circle in 24 hours, the notation adopted for right ascension was in terms of hours and minutes with 24 hours representing the full circle. Declination is expressed as an angle with respect to the celestial equator.

For example, the celestial coordinates of the star Betelgeuse in the constellation Orion are right ascension = 5 hours 52 minutes and the declination is 7 degrees 24 minutes. A declination south of the celestial equator is given a negative sign. Go Back Equinoxes and Solstices The points where the ecliptic crosses the equatorial plane of the celestial sphere are called equinoxes. On those dates there are 12 hours each of daylight and dark. The most northern excursion of the sun is called the summer solstice and will have the longest amount of daylight. The winter solstice opposite it is the shortest period of daylight. "At an equinox, the Sun is at one of the two opposite points on the celestial sphere where the celestial equator (i.e. declination 0) and ecliptic intersect. These points of intersection are called equinoctial points: classically, the vernal point (RA = 00h 00m 00s and longitude = 0�) and the autumnal point (RA = 12h 00m 00s and longitude = 180�).

The equinoxes are the only times when the solar terminator is perpendicular to the Equator. As a result, the northern and southern Hemispheres are equally illuminated." From Wiki . Index Go Back Celestial Measurement Celestial measurement is taken to mean the kinds of measurement with respect to the celestial sphere which allow you to locate astronomical objects for observation. Measurements with respect to the celestial sphere are typically expressed as right ascension and declination , measurements analogous to latitude and longitude on the Earth's surface. In order to know where to look in the sky for a given object, a precise description of the Earth's motion around the sun and precise measurement of time are necessary. It is often more convenient to describe the apparent motion of sun and stars with respect to the Earth as if it were fixed. In the Earth's frame of reference, the Sun's apparent path is called the ecliptic . The ecliptic plane is inclined at 23.5° with respect to the celestial equator because of the tilt of the Earth's rotation axis with respect to the plane of its orbit around the sun. Go Back Synodic and Sidereal Periods The period of a planet's orbital period around the Sun with respect to the distant stars is called its sidereal period.

The sidereal period of the Earth is about 365 1/4 days. Another type of period is useful for viewing the other planets - the period between the times their positions both lie on the same radial line from the sun, called the synodic period. When planets are on the same radial line from the sun, they are said to be "in opposition". For planets closer to the sun than the Earth, the synodic period of the Earth is longer than the sidereal period, and for outer planets it is shorter if seen by an observer on those planets. The sidereal period of Mars is 1.88 years, whereas the synodic period is 2.135 years as seen from the Earth. The time of opposition of Mars is associated with its apparent retrograde motion for an Earth observer. The period which brings the back to the same angular position with respect to the Sun is called the tropical year and is 365.242 mean solar days. Formally this period is defined as the interval of time from one vernal equinox to the next.

The sidereal period (period with respect to the distant stars) of 365.256 mean solar days is about 20 minutes longer because of the precession of the Earth's spin axis. That precession period of about 26,000 years brings the vernal equinox about 20 minutes earlier each year. The fact that the year is not exactly 365 days has led to the inclusion of the leap year days and other adjustments to the calendar. The sidereal day, which brings a "fixed" star back to the same position on the next night, is 23 hours 56 minutes and 4 seconds. The practical observable effect is that stars rise about 4 minutes earlier each night, about 2 hours earlier in a month, and appear as a parade that progresses westward across the night sky. Solstices and Equinoxes | My Dark Sky Lifelong companion under the stars Solstices and Equinoxes Solstice happens once every 6 months – Summer Solstice in June and Winter Solstice in December. Midway between the two solstices we have equinoxes – Vernal Equinox in March and Autumnal Equinox in September.

The reason we have solstices (or equinoxes) is exactly the same as why we have seasons: the Earth’s axis is tilted with respect to the ecliptic (the Sun’s path across the sky). Thus, the celestial equator and the ecliptic do not lie on the same plane, but cross each other at an angle of 23.5 degrees. Hence, there will be two points on the celestial sphere where the ecliptic crosses the celestial equator and two instants during the year when the Sun is at its greatest angular distance from the celestial equator. The intersection of the ecliptic and the celestial equator is known as the equinox. Since there are two intersections, there will be two equinoxes in a year: the Vernal (Spring) and the Autumnal Equinox. Spring and autumn officially begin at the instants of the vernal and autumnal equinox, respectively. Another way of defining equinox is the time when the Sun crosses the celestial equator. When the Sun crosses the equator from south to north, it’s Vernal Equinox; when it crosses from north to south, it’s Autumnal Equinox.

During equinoxes, the sun is directly over the Earth’s equator. At these times, the length of day and night are very nearly equal all over the world (equinox means “equal night”). On the equator, solar altitude (height of the Sun) reaches its maximum during the equinoxes (directly overhead or 90 degrees from the horizon). These are also the time when the Sun will rise exactly in the east and sets exactly in the west. Solstice, on the other hand, happens at the two instants when the Sun is at its greatest angular distance from the celestial equator. During the course of a year, the apparent motion of the Sun as seen from Earth moves from south to north and back to south again. When the Sun changes direction from north to south or vice verse, it seems to stands still momentarily. This point of time is known as the solstice. Solstice is derived from Latin word “solstitium”; “sol” meaning Sun, and “sistere” meaning stand still. When the Sun is at its farthest north position from the celestial equator, it’s Summer Solstice; and when it is at the farthest south position, it’s Winter Solstice.

Summer and winter officially begin at the instants of the summer and winter solstices, respectively. On the northern and southern hemisphere, the noontime Sun is highest in the sky during summer solstice and lowest in the sky during winter solstice. On the equator, however, we will only observe that the Sun is farthest north during summer solstice and farthest south during winter solstice. Solar altitude is the same during both summer and winter solstice (66.5 degrees from the horizon). Astronomy Picture of the Day has a nice photo showing the different position of the Sun for the northern hemisphere . Just bear in mind that this photo does not reflect our situation at the equator. At the equator, the “middle band” Sun should be directly overhead (at the zenith), while the solstice Suns (“top band” and “bottom band” Sun) are the same distance above the horizon. ~~~~~ As the Earth moves around the Sun, we will see that the Sun position in the sky at the same time everyday keeps on changing , sometimes from north to south, and sometimes the other way round.

Refer to the diagram below, which is a typical diagram we use to learn about seasons in school, due to the axis tilt of our planet with respect to its orbit around the Sun, sometimes our Earth’s northern axis is tilted towards the Sun and sometimes the southern axis is tilted towards the Sun. To visualise the Sun movement in the sky during the year, let’s start at the Vernal Equinox. On this day (more precisely, this point of time), the Sun shines on the equator. After this time, the Earth’s northern axis is tilted more and more towards the Sun, thus as seen from Earth, the Sun shifted its position towards the north. Then on Summer Solstice, the Sun will reach its farthest north position in the sky. After the Summer Solstice, the cycle reverses; as the Earth continues to revolve around the Sun, the Earth’s northern axis is now tilted lesser and lesser towards the Sun. Thus as seen from Earth, the Sun’s position in the sky now will be shifted towards the south until it again shines on the equator on Autumnal Equinox. After the Autumnal Equinox, the Sun will continue to moves south.

This time, the Earth’s southern axis will be tilted more and more towards the Sun until it reaches a maximum tilt on Winter Solstice. On our sky, the Sun will be moving towards the south everyday until it reaches its farthest south position in the sky on Winter Solstice. Then as the Earth moves towards the Vernal Equinox, our Earth’s southern axis tilt lesser and lesser towards the Sun – the Sun will now shift towards the north in our sky – until it again shines on the equator on Vernal Equinox and the cycle repeat itself. Although we usually said that the Sun rises in the east and set in the west, in reality the Sun rises exactly due east and set exactly due west only two times in a year, that is during the equinoxes. Other times the Sun will either rise northeast and set northwest (from March to September), or rise southeast and set southwest (from September to March of the following year). To observe this changing position of our Sun in the sky, try comparing its position everyday during sunrise or sunset against a reference point, for example against a building or a tree. Maybe you will not see any different in a day or two, but in weeks, you surely will notice that the Sun has moved.

Lastly, bear in mind that solstices and equinoxes only last an instant and not a whole day. In the case of the solstices, it’s the instant when the Sun “touches” its farthest north or south position and then “u-turn” back. It is the “u-turning” that makes the Sun seems to stands still momentarily. For the case of the equinoxes, it’s the instant when the Sun crosses the celestial equator. Having said that, these terms are usually loosely used to refer to the day within which the event occurs. Share this: Ecliptic | Space Wiki | Fandom powered by Wikia [ show ] Ecliptic and equator As the rotation axis of the Earth is not perpendicular to its orbital plane, the equatorial plane is not parallel to the ecliptic plane, but makes an angle of about 23°27' which is known as the obliquity of the ecliptic . The intersections of the equatorial and ecliptic plane with the celestial dome are great circles known as the celestial equator and the ecliptic. The intersection line of the two planes results in two diametrically opposite intersection points, known as the equinoxes .

The equinox which the Sun passes from south to north is known as the vernal equinox or first point of Aries . Ecliptic longitude , usually indicated with the letter λ, is measured from this point on 0° to 360° towards the east . Ecliptic latitude , usually indicated with the letter β is measured +90° to the north or -90° to the south. The same intersection point also defines the origin of the equatorial coordinate system, named right ascension measured from 0 to 24 hours also to the east and usually indicated with α or R.A., and declination , usually indicated with δ also measured +90° to the north or -90° to the south. Simple rotation formulas allow a conversion from α,δ to λ,β and back (see: ecliptic coordinate system ). Ecliptic and stars The ecliptic serves as the center of a region called the zodiac which constitutes a band of 8° on either side. Traditionally, this region is divided into 12 signs of 30° longitude each.

By tradition, these signs are named after 12 of the 13 constellations straddling the ecliptic. The zodiac signs are very important to astrologers . Modern astronomers typically use other coordinate systems today (see below). In the Indian tradition there are 27 Nakshatras , which cover 13°20’ of the ecliptic each. Each Nakshatra is divided into quarters or padas of 3°20’. The position of the vernal equinox is not fixed among the stars but due to the lunisolar precession slowly shifting westwards over the ecliptic with a speed of 1° per 72 years. A much smaller north/southwards shift can also be discerned, (the planetary precession, along the instantaneous equator, which results in a rotation of the ecliptic plane). Said otherwise the stars shift eastwards (increase their longitude) measured with respect to the equinoxes (in other words, as measured in ecliptic coordinates and (often) also in equatorial coordinates.

Using the current official IAU constellation boundaries — and taking into account the variable precession speed and the rotation of the ecliptic — the equinoxes shift through the constellations in the Astronomical Julian calendar years (in which the year 0 = 1 BC, -1 = 2 BC, etc.) as follows: [1] The March equinox passed from Taurus into Aries in year -1865, passed into Pisces in year -67, will pass into Aquarius in year 2597, will pass into Capricorn in year 4312. It passed along (but not into) a 'corner' of Cetus on 0°10' distance in year 1489. The June solstice passed from Leo into Cancer in year -1458, passed into Gemini in year -10, passed into Taurus in December year 1989, will pass into Aries in year 4609. The September equinox passed from Libra into Virgo in year -729, will pass into Leo in year 2439.

The December solstice passed from Capricorn into Sagittarius in year -130, will pass into Ophiuchus in year 2269, and will pass into Scorpius in year 3597. Ecliptic and Sun Due to perturbations to the Earth's orbit by the other planets, the true Sun is not always exactly on the ecliptic, but may be some arcseconds north or south of it. It is therefore the centre of the mean Sun which outlines its path. As the Earth revolves in one year around the Sun, it appears that the Sun also needs one year to pass the whole ecliptic. With slightly more than 365 days in the year, the Sun moves almost 1° eastwards every day (direction of increasing longitude). This annual motion should not be confused with the daily motion of the Sun (and the stars, the whole celestial sphere for that matter) towards the west in 24 hours and along the equator.

In fact where the stars need about 23h56m for one such rotation to complete, the sidereal day , the Sun, which has shifted 1° eastwards during that time needs 4 minutes extra to complete its circle, making the solar day just 24 hours. The mean Sun crosses the equator around 21 March in the vernal equinox, its declination, right ascension, and ecliptic longitude are all zero then (the ecliptic latitude is always). The March equinox marks the onset of spring in the northern hemisphere and autumn in the southern. As such the term "spring equinox" should be avoided. The actual date and time varies from year to year because of the occurrence of leap years . It also shifts slowly over the centuries due to imperfections in the Gregorian calendar. Ecliptic longitude 90°, at right ascension 6 hours and a northern declination equal to the obliquity of the ecliptic (23.44°), is reached around 22 June. This is the June solstice or summer solstice in the northern hemipshere and winter solstice in the southern hemisphere.

It is also the first point of Cancer and directly overhead on Earth on the tropic of Cancer so named because the Sun turns around in declination. Ecliptic longitude 180°, right ascension 12 hours is reached around 23 September and marks the second equinox or first point of Libra . Due to perturbations to the Earth orbit, the moment the real Sun passes the equator might be several minutes earlier or later. The southern most declination of the sun is reached at ecliptic longitude 270°, right ascension 18 hours at the first point of the sign of Capricorn around 22 December. In any case it must be stressed that although these traditional signs (in western tropical astrology ) have given their names to the solstices and equinoxes, in reality, (as from the list in the previous chapter) the cardinal points are currently situated in the constellations of Pisces, Taurus, Virgo and Sagittarius respectively. Ecliptic and planets Most planets go in orbits around the sun which are almost in the same plane as the Earth's orbital plane, differing by a few degrees at most.

As such they always appear close to the ecliptic when seen in the sky. Mercury with an orbital inclination of 7° or Pluto with 17° are exceptions. Many minor planets have large inclinations too. The intersection line of the ecliptical plane and another planet's orbital plane is called the nodal line of that planet, and the nodal line's intersection points on the celestial sphere are the ascending node (where the planet crosses the ecliptic from south to north) and the diametrically opposite descending node . Only when an inferior planet passes through one of its nodes can a transit over the Sun take place. Inclination and nodal lines, as almost all other orbital elements, change slowly over the centuries due to perturbations from the other planets. Ecliptic and Moon The orbit of the Moon is inclined by about 5° on the ecliptic. Its nodal line is not fixed either, but regresses (moves towards the west) over a full circle every 18.6 years. This is the cause of nutation and lunar standstill . The moon crosses the ecliptic about twice per month. If this happens during new moon a solar eclipse occurs, during full moon a lunar eclipse .

This was the way the ancients could trace the ecliptic along the sky; they marked the places where eclipses could occur. Ecliptic and star coordinates Up to the 17th century, starmaps and positions in star catalogues were always given in ecliptical coordinates. It was not until astronomers started to use telescopes to measure star positions that equatorial coordinates came in use, and so exclusively that nowadays ecliptical coordinates are no longer used. This is not always desirable. A planetary conjunction for example would be much more illustratively described by ecliptic coordinates than equatorial. Also see zodiacal coordinates.

Question: What is the name for the point on the ecliptic when the sun is at its greatest distance from the equator?
Answer: Solstice