◑ Moon phase journal: one line for each of the eight phases, on a sheet for the month

Umbriel's free Lunation Sheet is a moon phase journal with the timing done for you. Each Moon month gets one sheet with eight boxes, one for each phase from New Moon to balsamic. The box for the phase the Moon is in right now is open for a line; the next box carries its own date and time in your clock. When the month ends, the sheet closes into a printable engraved plate.

• What you'll needA few seconds; no chart and no account
• What you getA sheet for the current Moon month with eight phase boxes, the exact start of each phase in your own time zone, one line of your own in each box you fill, and a printable plate when the lunation ends
• CostFree, no account required

A moon phase journal is a lovely idea that mostly dies in a notebook, because nobody remembers when the first quarter is. The Lunation Sheet remembers for you. It works out when each of the eight phases begins, to the minute, and opens the right box at the right time.

The eight phases are the classical ones: New Moon, waxing crescent, first quarter, waxing gibbous, Full Moon, waning gibbous, last quarter and balsamic. Each is one eighth of the Moon's circuit away from the Sun, so a phase lasts about three and a half days. The box for the phase the Moon is in right now takes a line in a few seconds, and you can add a small mark in one of the plate's inks if you like.

The next box always shows when it opens, as a date and a time in your own clock. That is the whole reason to come back: a few days off, and written on the sheet rather than sent as a nag.

When the lunation ends, the sheet closes into an engraved plate you can print. A box you never filled is drawn as cloud cover, so a month with one line in it is a finished sheet and prints as well as a month with eight. There is no score, no count of boxes filled and nothing that says you missed anything. A cloud is weather.

Every phase's exact instant and how much of the Moon was lit are copied into the sheet when you write, so an old plate never shifts. Your lines stay private: they live on your device, and if you sign in they sync end to end encrypted, the same way the journal does. Nothing on the sheet is ever posted.

If you would rather draw the Moon than write about it, Draw the Moon is the nightly companion: one disc, from what you think it looks like. The Lunation Sheet is the month; they keep separate pages and never ask you to do both.

A phase begins at the instant the angle between the Moon and the Sun, measured along the ecliptic, reaches a multiple of 45°: 0° for the New Moon, 90° for the first quarter, 180° for the Full Moon, and the in-between phases at 45°, 135°, 225°, 270° and 315°. Each instant is found by scanning the engine's own Sun-Moon angle and then bisecting it to the second, the same method the engine uses for the four principal phases, and an offline check holds the four shared ones to within a second of the engine's own. The sheet's error bar is derived rather than remembered: the Moon's longitude is measured against JPL's ephemeris at worst 0.27 arcminutes to 2050 and the Sun's at under an arcsecond, so the angle between them is good to about 0.29 arcminutes; divided by how fast that angle is changing at each boundary, which is about 30 arcminutes an hour, that is roughly half a minute of time. Every time on the sheet is shown in your device's own time zone. When you write in a box, the phase's instant and the fraction of the Moon lit are copied into your entry, so a printed plate never changes if the engine is improved later. A lunation runs from one New Moon to the next, about 29.5 days, and its sheet closes at the second New Moon.