Moonrise and Moonset: Why the Time Keeps Shifting

Almost everyone looking at a lunar calendar for the first time is surprised by one thing: the moonrise time matches nothing and changes the next day. The difference between neighbouring days is small — about an hour — but over a month about a full day accumulates, and because of that the familiar "the Moon rises around sunset" works only for a few days around full moon. Let us take apart where this shift comes from.

The main number: the shift is always positive, but varies

The moonrise time slips backward, i.e. becomes later, every day — otherwise it could not run through a full circle in a month. But the size of this lag varies sixteenfold: from 6 minutes to 1 hour 37 minutes on the same days of the year.

Data for Moscow for September 2026, excluding two days with duplicated events:

The mean over 36 measured days is about 60 minutes for moonrise and about 41 minutes for moonset. Averaged together these two numbers give (60 + 41) / 2 ≈ 51 — the familiar ~49 minutes of the usual empirical rule; the difference is that for moonrise and moonset these minutes diverge almost in antiphase instead of being split evenly between them.

The Sun behaves evenly: two minutes a day, the same across the whole table.

Why it happens: the Moon shifts eastward against the rotation of the sky

A day is a 360° turn of the sky, and in that time the Moon shifts against the stars by about 13 degrees eastward. East is opposite to the direction of the daily rotation of the sky, so the Moon rises later every day.

The operative motion here is the rotation of the sky westward, while the Moon shifts eastward. These are two opposite motions, and their difference is what produces the daily lag.

The size of the lag varies because the angle between the ecliptic and the horizon changes through the year. In early September on the morning horizon the ecliptic climbs steeply and the Moon crosses the horizon fast, so the lag is large. At another time of year and at other points of the horizon it lies shallow, and the lag shrinks to its minimum. That is why the peak and the trough fall in the middle of the month rather than at its edges.

The Sun does have its own motion across the sky — about a degree a day eastward — which is why its rise time drifts by a full day over a year. The combination of this motion, the obliquity of the ecliptic, the eccentricity of the orbit and the latitude of the city is what gives the two minutes a day. It cannot be reduced to a single factor: all four are at work.

A full day accumulates over the month

An average 50 minutes over a synodic month of 29.53 days gives roughly 24 hours. So in a month the moonrise time makes a full circle clockwise and returns to the same hour it started from. The same arithmetic holds for moonset — which is why the averaged 50 minutes fall on each of the two moments rather than being divided in half between them.

The table of rises looks like this:

This is exactly the table worth memorising: the phase determines the time the Moon appears in the night sky, not its brightness. At new moon there is no Moon in the night sky because it is physically not there, while at first quarter it occupies the whole evening.

Relation to the lunar day and the start time

In the "Day starts" column of the general calendar stands the start time of the lunar day. It almost coincides with the moonrise time, and that is no coincidence: lunar days were historically counted from moonrise.

In the real data for 12 September 2026 lunar day 1 begins at 06:27 under the lunar.day dating convention, while moonrise that day is at 07:32. The gap of over an hour arises because the start of the lunar day is set by the grid of lunar days (details in the article "How to read a lunar calendar": read the day card), and coincides neither with the new-moon instant nor with moonrise. In practice this means the start time of the lunar day is not equal to the moonrise time — although it moves at the same rate.

Latitude changes the picture

Everything said above holds at any latitude, but the scale of the difference depends strongly on latitude.

At middle latitudes the span of the rise time over a month is a full day, and the Moon is available at different times of day without long gaps. At high latitudes in winter the difference between the extreme values reaches tens of hours, and in polar regions there are days when the Moon does not rise or set at all.

The practical consequence: the advice "the Moon is best seen in the evening" applies to middle latitudes and stops working in the north in winter. If you are planning observations at high latitudes, work from the rise and set table rather than from habit.

What to do with this data

Two practical conclusions worth taking from the table above.

First: the first quarter is the main evening object. It rises around noon, stands in the southern part of the sky at sunset and sets around midnight, so it occupies the whole evening. For observations after midnight you need the full moon and the last quarter. At new moon, by contrast, the Moon truly does not appear in the night sky: it rises and sets with the Sun.

Second: if you are waiting for the Moon on a particular night, check the set table, not the rise table. For evening observations what matters is when the Moon sets; for night observations you need when it rises and when it sets, i.e. the full interval.

How to view rise times on lunar.day

The dedicated page /moon/rise-set/{date} shows two times for the chosen city: moonrise and moonset in the local time zone. The page currently outputs neither sunrise, nor culmination, nor the interval above the horizon. If you need sunrise for comparison, it is in the general lunar calendar and in the table below.

Over a month you can see how the grid of times shifts — the most visual way to see the rule from the first section in action.

Summing up

The Moon rises later than on the previous day because it shifts eastward against the stars while the sky rotates westward. Moonrise and moonset shift by about 60 and 41 minutes on average respectively (Moscow, September 2026); over a full month each of the two means is close to the usual 49 minutes, so the moonrise time runs through a full circle in a month: at new moon the Moon rises with the Sun, at full moon at sunset. The spread in both figures is set by the angle between the ecliptic and the horizon: it depends on the season and the latitude. Latitude sets the scale of the differences: at middle latitudes the Moon is available at different times of day, at high latitudes in winter there are days when it does not rise at all.