EQUINOX (from the Lat. aequus, equal, and nox, night)

This article appears in Volume V09, Page 724 of the Encyclopedia Britannica.

Encyclopedia Britannica - Main :: EMS-EUD

EQUINOX (from the Lat. aequus, equal, and nox, night) , a

term

TERM

used to express either the moment at which, or the point at which, the sun apparently crosses the

celestial

CELESTIAL, OR STELLAR

equator

EQUATOR (
Late
- LATE
Lat. aequator, from aequare, to make equal)

. Since the sun moves in the

ecliptic

ECLIPTIC

, it is in the last-named sense the point of intersection of the

ecliptic

ECLIPTIC

and the

celestial

CELESTIAL, OR STELLAR

equator

EQUATOR (
Late
- LATE
Lat. aequator, from aequare, to make equal)

. This is the usual meaning of the

term

TERM

in astronomy. There are
two such points, opposite each other, at one of which the sun crosses the equator toward the north and at the other toward the

south

SOUTH
SOUTH, ROBERT (1634–1716)

. They are called vernal and autumnal respectively, from the relation of the corresponding times to the seasons of the northern hemisphere. The line of the equinoxes is the imaginary

diameter

DIAMETER (from the Cr. &a, through, µErpov, measure)

of the celestial sphere which joins them.
The vernal

equinox

EQUINOX (from the Lat. aequus, equal, and nox, night)

is the initial point from which the right ascensions and the longitudes of the heavenly bodies are measured (see ASTRONOMY: Spherical). It is affected by the motions of Precession and Nutation, of which the former has been known since the time of Hipparchus. The actual

equinox

EQUINOX (from the Lat. aequus, equal, and nox, night)

is defined by first taking the conception of a fictitious point called the Mean Equinox, which moves at a nearly uniform rate, slow varying, however, from century to century. The true equinox then moves around the mean equinox in a period equal to that of the moon's nodes. These two motions are defined with greater detail in the articles PRECESSION OF THE EQUINOXES and NUTATION.
Equinoctial Gales.At the time of the equinox it is commonly believed that strong gales may be expected. This popular idea has no foundation in fact, for continued observations have failed to show any unusual prevalence of gales at this season. In one case observations taken for fifty years show that during the five days from the 21st to the 25th of

March

and September, there were fewer gales and storms than during the preceding and succeeding five days.

End of Article: EQUINOX (from the Lat. aequus, equal, and nox, night)

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