Equinox was a long-running Channel 4 popular science and documentary programme. The series ran from 1986 to 2001, originally aired on a weekly basis. The number of films per series fell over the years, from eighteen one-hour films a year originally to twelve by the late 1990s. The last regular series was shown in 2001, with six films. One-off films have occasionally been aired under the title "Equinox Special".

Equinox - Netflix

Type: Documentary

Languages: English

Status: Ended

Runtime: 60 minutes

Premier: 1986-07-31

Equinox - Equinox - Netflix

An equinox is commonly regarded as the moment the plane (extended indefinitely in all directions) of Earth's equator passes through the center of the Sun, which occurs twice each year, around 20 March and 22-23 September. In other words, it is the point in which the center of the visible sun is directly over the equator. However, because the moon (and to a lesser extent the other planets) cause the true motion of the Earth to vary from a perfect ellipse, the equinox is now officially defined by the Sun's more regular ecliptic longitude rather than latitude. The instants of the equinoxes are currently defined to be when the longitude of the Sun is 0° and 180°. There are tiny (up to 1¼ arcsecond) variations in the Sun's latitude (discussed below), which means the Sun's center is rarely precisely over the equator under the official definition. The two understandings of the equinox can lead to discrepancies of up to 69 seconds. On the day of an equinox, daytime and nighttime are of approximately equal duration all over the planet. They are not exactly equal, however, due to the angular size of the Sun and atmospheric refraction. The word is derived from the Latin aequinoctium, from aequus (equal) and nox (genitive noctis) (night).

Equinox - Celestial coordinate systems - Netflix

The March equinox occurs about when the Sun appears to cross the celestial equator northward. In the Northern Hemisphere, the term vernal point is used for the time of this occurrence and for the precise direction in space where the Sun exists at that time. This point is the origin of some celestial coordinate systems, which are usually rooted to an astronomical epoch since it gradually varies (precesses) over time: in the ecliptic coordinate system, the vernal point is the origin of the ecliptic longitude; in the equatorial coordinate system, the vernal point is the origin of the right ascension.

Strictly speaking, at the equinox, the Sun's ecliptic longitude is zero. Its latitude will not be exactly zero, since Earth is not exactly in the plane of the ecliptic. Its declination will not be exactly zero either. (The ecliptic is defined by the barycenter of Earth and the Moon combined.) The modern definition of equinox is the instants when the Sun's apparent geocentric longitude is 0° (northward equinox) or 180° (southward equinox). See the adjacent diagram. Because of the precession of the Earth's axis, the position of the vernal point on the celestial sphere changes over time, and the equatorial and the ecliptic coordinate systems change accordingly. Thus when specifying celestial coordinates for an object, one has to specify at what time the vernal point and the celestial equator are taken. That reference time is called the equinox of date. The autumnal equinox is at ecliptic longitude 180° and at right ascension 12h. The upper culmination of the vernal point is considered the start of the sidereal day for the observer. The hour angle of the vernal point is, by definition, the observer's sidereal time. Using the current official IAU constellation boundaries – and taking into account the variable precession speed and the rotation of the celestial equator – the equinoxes shift through the constellations as follows (expressed in astronomical year numbering when the year 0 = 1 BC, −1 = 2 BC, etc.): The March equinox passed from Taurus into Aries in year −1865, passed into Pisces in year −67, will pass into Aquarius in year 2597, and then into Capricornus in year 4312. In 1489 it came within 10 arcminutes of Cetus without crossing the boundary. The September equinox passed from Libra into Virgo in year −729, will pass into Leo in year 2439.

Equinox - References - Netflix