The hours of the day

How this one is built

The first hour after sunrise belongs to the planet the day is named after: Sunday to the Sun, Monday to the Moon, Saturday to Saturn. Every hour after it steps one place along the Chaldean order — Saturn, Jupiter, Mars, Sun, Venus, Mercury, Moon — which is the planets sorted by how slowly they appear to move. Walk that through twenty-four hours and the first hour of the next day lands exactly on the next day’s planet. That is the traditional explanation for the order of the days of the week, and the fact that the system closes on itself is the most interesting thing about it.

The hours themselves are unequal by design. Daylight is divided into twelve whatever its length, so in London in June a day hour runs to over eighty minutes and a night hour the same day to under forty. On the equinoxes they are both sixty, which is why equal hours were once called equinoctial hours.

What an hour is traditionally used for is given as a quality, not an instruction: a way of choosing when to do something you were going to do anyway. There is no measured effect of the hour of the day on the outcome of a letter or a conversation, and nothing on this page predicts anything.

What the page works out, step by step

Once a place is chosen, the page searches for the last sunrise there on or before this minute, the sunset after it and the sunrise after that, using the same astronomy as the birth chart. The span from sunrise to sunset is divided into twelve equal day hours, and the span from sunset to the next sunrise into twelve equal night hours. The first day hour goes to the planet of the weekday that sunrise fell on, and each hour after it to the next planet in the Chaldean order. The hour you are in is marked, and the dial is redrawn once a minute while the page is open. The same sunrise and sunset give the times of civil, nautical and astronomical twilight in the list under the hours.

Reading the dial, with an example

Sunrise is at the top of the dial, and the width of each sector is the length of its hour, so in summer the day sectors are visibly wider than the night ones. The middle names the hour you are in, or whichever one you point at or step to with the arrow keys.

Say it is a Tuesday, and the Sun rises at 06:00 and sets at 20:00. Fourteen hours of daylight make each day hour seventy minutes long, and ten hours of night make each night hour fifty. Tuesday belongs to Mars, so the first hour, 06:00 to 07:10, is Mars’s; the second, 07:10 to 08:20, goes to the Sun, and then come Venus, Mercury, the Moon, Saturn and Jupiter, until the eighth hour returns to Mars. Carry on round and the twenty-fifth hour, the first after Wednesday’s sunrise, falls to Mercury, and Wednesday is Mercury’s day. French and Spanish keep the planets in the names plainly: mardi and martes for Mars, mercredi and miércoles for Mercury.

Where it stops working, and other snags

Inside the polar circles there are days when the Sun does not rise or does not set. There is then no daylight to divide, and the page says so rather than inventing hours. Close to that line in summer, the night hours shrink to a few minutes each.

The day of the hours begins at sunrise, not at midnight, so at one in the morning you are still in the night hours of the day before; the caption under the dial names the sunrise the day began at. Daylight saving changes the numbers on the clock but not the hours themselves, which are cut from sunrise and sunset. Times are shown by the clock of this device, but the weekday, and so the planet of the day, is the place’s own: a city far to the east or west gets the planet of the date its sunrise falls on there.

For sunrise, sunset and the twilights on every day of the year at the same place, see Daylight; for where the Sun rises and how high it climbs, Sun path. The seven planets that own the hours are described one by one on The planets, and the Moon’s phase and sign today are on The Moon.