The description and use of the globes and the orrery / To which is prefix'd, by way of introduction, a brief account of the solar system

by Joseph Harris

A Week.

A Week is a system of seven days, in which each day is distinguished by a different name. In most countries these days are called after the names of the seven Planets, as above noted. All nations that have any notion of religion, lay apart one day in seven for public worship; the day solemnized by Christians is Sunday, or the first day of the week, being that on which our saviour rose from the grave, on which the apostles afterwards used more particularly to assemble together to perform divine worship. The Jews observed Saturday, or the seventh day of the week, for their sabbath, or day of rest, being that appointed in the fourth commandment under the Law. The Turks perform their religious ceremonies on Friday.

A Month.

Periodical and Synodical Month.

A Month is properly a certain space of time measured by the Moon in his course round the Earth. A Lunar Month is either Periodical or Synodical. A Periodical Month is that space of time the Moon takes to perform her course from one point in the ecliptic ’till she arrives to the same again, which is 27 days, and some odd hours; and a Synodical Month is the time betwixt one new Moon, and the next new Moon, which is commonly about 29½ days. But a Civil Month, is different from these, and consists of a certain number of days, fewer or more, according to the laws and customs of the country where they are observed.

A Year Sydereal and Tropical.

The compleatest period of time is a Year, in which all the variety of seasons return, and afterwards begin anew. A Year is either Astronomical or Civil. An Astronomical Year is either a Sydereal wherein the Sun departing from a fixed Star, returns to it again; or Tropical, which is the space of time the Sun takes to perform his course from any point of the ecliptic, ’till he returns to it again.

A Tropical Year consists of 365 days, 5 hours, and 49 minutes; this is the time in which all the seasons compleatly returns, which is a small matter less than a Sydereal Year.

Egyptian Year.

The Civil Year is the same with the Political established with the laws of a country; and is either moveable or immoveable. The moveable year consists of 365 days, being less than the tropical year by almost six hours, and is called the Egyptian Year, because observed in that Country.