21.6.17

Summer solstice 2017

The Solstice occurs twice each year (around June 21 and December 22) as the Sun reaches its most northerly or southerly excursion relative to the celestial equator on the celestial sphere. The seasons of the year are directly connected to both the solstices and the equinoxes.

The term solstice can also be used in a broader sense, as the day when this occurs. The day of the solstice has either the most sunlight of the year (summer solstice) or the least sunlight of the year (winter solstice) for any place other than the equator. Alternative terms, with no ambiguity as to which hemisphere is the context, are June solstice and December solstice, referring to the months of year in which they take place.

At latitudes outside the tropics, the summer solstice marks the day when the sun appears highest in the sky. Within the tropics, the sun appears directly overhead (called the subsolar point) from days to months before the solstice and again after the solstice, which means the subsolar point occurs twice each year.

The word solstice is derived from the Latin sol (sun) and sistere (to stand still), because at the solstices, the Sun stands still in declination; that is, the seasonal movement of the Sun's path (as seen from Earth) comes to a stop before reversing direction.

The summer solstice (or estival solstice), also known as midsummer, occurs when a planet's rotational axis, or geographic pole on either its northern or its southern hemisphere, is most inclined toward the star that it orbits. On the summer solstice, Earth's maximum axial tilt toward the Sun is 23.44°. (Likewise, the Sun's declination from the celestial equator is +23.44° in the Northern Sky and −23.44° in the Southern Sky.) This happens twice each year (once in each hemisphere), when the Sun reaches its highest position in the sky as seen from the north or south pole.

The summer solstice occurs during the hemisphere's summer. This is the northern solstice in the Northern Hemisphere and the southern solstice in the Southern Hemisphere. Depending on the shift of the calendar, the summer solstice occurs some time between June 20 and June 22 in the Northern Hemisphere and between December 20 and December 23 each year in the Southern Hemisphere. The same dates in the opposite hemisphere are referred to as the winter solstice.

As seen from a geographic pole, the Sun reaches its highest altitude of the year on the summer solstice. It can be solar noon only along that longitude, which at that moment lies in the direction of the Sun from the pole. For other longitudes, it is not noon. Noon has either passed or has yet to come. Hence the notion of a solstice day is useful. The term is colloquially used like "midsummer" to refer to the day on which solstice occurs. The summer solstice day has the longest period of daylight, except in the polar regions, where daytime remains continuous for 24 hours every day during a period ranging from a few days to six months around the summer solstice.

The concept of the solstices was embedded in ancient Greek celestial navigation. As soon as they discovered that the Earth is spherical[6] they devised the concept of the celestial sphere, an imaginary spherical surface rotating with the heavenly bodies (ouranioi) fixed in it (the modern one does not rotate, but the stars in it do). As long as no assumptions are made concerning the distances of those bodies from Earth or from each other, the sphere can be accepted as real and is in fact still in use.

The stars move across the inner surface of the celestial sphere along the circumferences of circles in parallel planes perpendicular to the Earth's axis extended indefinitely into the heavens and intersecting the celestial sphere in a celestial pole. The Sun and the planets do not move in these parallel paths but along another circle, the ecliptic, whose plane is at an angle, the obliquity of the ecliptic, to the axis, bringing the Sun and planets across the paths of and in among the stars.*

Cleomedes states:

The band of the Zodiac (zōdiakos kuklos, "zodiacal circle") is at an oblique angle (loksos) because it is positioned between the tropical circles and equinoctial circle touching each of the tropical circles at one point ... This Zodiac has a determinable width (set at 8° today) ... that is why it is described by three circles: the central one is called "heliacal" (hēliakos, "of the sun").

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. Other authors use Zodiac to mean ecliptic, which first appears in a gloss of unknown author in a passage of Cleomedes where he is explaining that the Moon is in the zodiacal circle as well and periodically crosses the path of the Sun. As some of these crossings represent eclipses of the Moon, the path of the Sun is given a synonym, the ekleiptikos (kuklos) from ekleipsis, "eclipse".

According to ancient Greeks, Tammuz becomes Adonis (Lord). This is a time that is also sacred to all high priestesses and hiereias (female guardians of temples and communities). It is also the sacred time of Athena (Goddess of wisdom). For the Greeks, the New Year began on the first new moon after the summer solstice. It was celebrated by a festival to Athena so that rain would come to the crops. A procession was held in which food offerings and new cloths were brought to Her statue. The statue was cleaned and then dressed in this new finery. Midsummer was also the time to honor Prometheus (Sun Wheel) for stealing fire from the Gods and bringing it to His creation – mankind.

Δεν υπάρχουν σχόλια:

Δημοσίευση σχολίου

loading...

Popular Posts Of The Week

Top best cpc cpm ppc ad network for publisher

Αναγνώστες

Translate

loading...
...
loading...
---------------------------------------------------------------------------