Equinox

[T]he Months of March and September, the tvvo Æquinoxes of Our year, are the moſt vvindy and tempeſtuous, the moſt unſettled and unequable of Seaſons in moſt Countries of the VVorld.

The four grand and ſolemn Bardic days are, of ancient uſage, the tvvo equinoxes, and the tvvo ſolſtices; the nevv and full moons are alſo, ſubordinately, ſolemn Bardic days: […]

[H]e [Milton] believed, his poetic vein only flowed from the autumnal to the vernal equinox; and, in his essay on Education, he doubts whether, in the fine days of spring, any study can be accomplished by young men.

Live long, nor feel in head or chest / Our changeful equinoxes, / Till mellow Death, like some late guest, / Shall call thee from the boxes.

21. Report the experiments, if conveniently they may, at both the solstices and equinoctes. / 22. Observe accurately the time of the sun’s rising on the top of the hill and below, and note the difference.

For [Julius] Cæsar says, that on the night of the fourth day after his landing there was a full moon. He had before mentioned that the summer was far spent, and the æquinox not come, hence, the full moon must have been either in July or August.

The word equinox is generally taken to refer to the days when, at every point on the earth, day and night are of equal length. But this definition of the equinox is a bit misleading. Since it gets light before the sun rises and remains light after the sun sets, the actual period of darkness at the equinox will be substantially less than twelve hours, the exact amount depending on latitude and how one defines the boundary between twilight and night. […] In practice, one cannot determine the equinox by measuring the length of time between sunrise and sunset.

[…] Midsummer’s Day falls near the beginning of summer meteorologically, but was the midpoint of summer in the traditional calendar. Though Midsummer’s Day celebrations are common in the modern Celtic countries, there is no evidence that the ancient Celts celebrated either the solstices or the equinoctes.

[D]oe but ſee his vice, / Tis to his vertue, a iuſt equinox, / The one as long as th'other: […]

The paſſage yet vvas good, the vvind, 'tis true, / VVas ſomevvhat high, but that vvas nothing nevv, / Nor more than uſual Equinoxes blevv.

The Equinox drove the sand into their faces or round their legs, as they dived among the sheep-haunted hollows.

[T]hey [seals] are over all the American Coaſt of the South Seas, from Terra del Fuego, up to the Equinoctial Line: but to the North of the Equinox again, in theſe Sea, I never ſavv any, till as far as 21 North Lat[itude].