The Day the Moon Does Not Rise: Why Moonrise Skips a Day Every Month

The Short Answer

The Moon takes on average 24 hours 50 minutes (24.84 hours) to come back to the same place in the sky, so moonrise comes about 50.5 minutes later each day. The lost minutes add up to a whole day once a lunar month: about once a month a calendar day has no moonrise at all, and about two weeks earlier another has no moonset. In 2027 Mecca, London, Istanbul, Karachi, Jakarta, New York and Cape Town each have 12 days with no moonrise and 12 with no moonset, by their own clocks. The day with no moonrise falls near the last quarter: in Mecca always within 1.7 days of it. Far north, in Tromsø, the Moon stays above or below the horizon all day on 162 days of 2027, for up to eight days in a row.

Why Moonrise Is Later Every Day

The Earth turns once a day, but in that day the Moon moves on in its orbit, eastwards against the stars, by about 12 degrees relative to the Sun. The Earth has to turn a little more than once before the Moon is back on the eastern horizon. Over one synodic month of 29.53 days the Moon falls behind the Sun by a full turn, so in 29.53 days there are only 28.53 moonrises. That makes the mean lunar day 24 x 29.53 / 28.53 = 24.84 hours, and the mean delay 50.5 minutes.

The engine of this site confirms the average city by city: in every one of the seven cities there are 353 moonrises in the 365 days of 2027, with a mean delay of 50.4 to 50.5 minutes. The other 12 days are the days with none.

The Moon's crossing of the meridian, its highest point in the sky, keeps the same rhythm: once every 24 hours 50 minutes on average, which is the clock behind when the Moon stands over the Kaaba.

A Delay That Changes Through the Month

The 50.5 minutes is only an average. How much later the Moon rises from one day to the next depends on the angle at which its path meets the horizon, and on whether it is moving north or south in the sky. Near the equator the Moon always rises steeply and the delay stays close to the average; at higher latitudes it swings widely.

The best known case is the harvest moon, the full moon nearest the September equinox. At that full moon the Moon is moving north fastest, and in the northern hemisphere its path meets the evening horizon at a shallow angle, so it rises only a little later each evening. After the full moon of 15 September 2027 (23:04 UTC), moonrise in London comes only 12, 13, 15 and 20 minutes later on the four evenings that follow; in Mecca 32 to 40 minutes. Six months earlier, after the full moon of 22 March 2027, the delay in London is 80 to 84 minutes and in Mecca 58 to 59. In Reykjavik, at 64 degrees north, the September full moon even rises 6 to 8 minutes earlier each evening. The geometry is explained in why the Moon's path across the sky changes every month.

The Day With No Moonrise

When the delay carries moonrise past midnight, one calendar day is skipped. In Mecca in September 2027 the Moon rises at 23:55 on 23 September, and the next moonrise is at 01:00 on 25 September. 24 September has no moonrise. Two weeks before, the same happens to moonset: the Moon sets at 23:24 on 7 September and next at 00:16 on 9 September, so 8 September has no moonset.

The figure shows the whole month, in Mecca and in Tromsø, by the local clock:

Every day of 2027 with no moonrise, by each city's own calendar and time zone, with daylight saving time where the city uses it:

And every day with no moonset:

The dates differ from city to city by a day or two because moonrise depends on latitude as well as longitude, and because a time zone's clock can be well ahead of or behind the Sun: London on 25 February, Mecca on 27 February. Since there are 12.4 lunar months in a year, a year has 12 or 13 such days. In Mecca from 2026 to 2035 the count is 13, 12, 12, 13, 12, 12, 13, 12, 12 and 13: 124 days in ten years, one per lunar month.

Which Phase of the Moon

The Moon rises at about midnight when it is at last quarter, half lit, 90 degrees west of the Sun. So the night on which moonrise slips from just before midnight to just after is near the last quarter, and the day with no moonrise is the day after that slip. On 24 September 2027 in Mecca the last quarter was at 13:21 the day before.

• In Mecca, every day without a moonrise in 2027 falls within 1.7 days of the last quarter, with the Moon 39 to 66 per cent lit at noon.
• In Jakarta, near the equator, it is always within a day: from 0.5 days before the last quarter to 0.8 days after.
• In London it moves around much more, from 5.1 days before the last quarter to 2.4 days after. On 23 May 2027 the day without a moonrise comes while the Moon is still a waning gibbous, 91 per cent lit, because a Moon far south of the equator rises late in the night at that latitude.

The day with no moonset is the mirror image. The Moon sets at about midnight at first quarter, so the day without a moonset is near the first quarter: in Mecca within 1.8 days of it, in London from 4.0 days before to 2.3 days after.

For moon watching this has a practical side. A day without a moonrise does not mean a day without the Moon: on 24 September 2027 the Moon is above Mecca from midnight until it sets at 13:53, a half Moon in the morning sky. What it does mean is that the evening is dark: the Moon will not come up until after the next midnight. In the same way, the evening of a day without a moonset has the first-quarter Moon in the sky until after midnight.

Does It Change the Hijri Date?

No. A Hijri month begins with the new crescent, or with a calculated date, at the start of the month, and nothing that happens to moonrise later in the month moves it. The Islamic day also begins at sunset, not at midnight, so "a calendar day with no moonrise" is a feature of the midnight-to-midnight civil calendar.

It is still a regular part of the Hijri month. By the Umm al-Qura calendar used in Saudi Arabia, Mecca's days without a moonrise in 2027 fall on the 20th to 23rd of the month, and its days without a moonset on the 5th to 8th. For how the month begins, see how the Islamic lunar calendar works.

Near the Arctic: The Moon Up or Down for Days

At high latitudes the Moon does not just skip a rise now and then. When it is far enough north of the celestial equator, roughly more than 90 degrees minus the latitude, it circles the sky without setting; when it is as far south, it does not rise at all. In 2027 the Moon reaches up to 27.7 degrees north and south of the equator, well past the 20 degrees or so that matter at Tromsø (69.6 degrees north).

In Tromsø every month of 2027 has days with the Moon up from midnight to midnight and days with it down all day. The longest spell above the horizon is 7.1 days, from 04:24 on 12 March to 06:40 on 19 March (local time); the longest below it is 8.1 days, from 06:58 on 29 January to 09:34 on 6 February. In Reykjavik the longest are 4.0 days (13 to 17 March) and 5.0 days (30 January to 4 February).

The seasons make this striking. The full moon stands opposite the Sun, so in midwinter it is far north. Around the full moon of 13 December 2027 the Moon stays up in Tromsø from 11 to 15 December, in the polar night: on 13 December the Sun does not rise at all. In midsummer it is the other way round: around the full moon of 19 June 2027 the Moon does not rise from 15 to 21 June, under the midnight sun: on 19 June the Sun does not set. High latitudes also allow the opposite of a skipped day: in Reykjavik the Moon rises twice on 30 June 2027, and in Tromsø twice on 25 June.

This depends on the 18.6-year cycle of the Moon's path. At the minor standstill of 2034 the Moon reaches only 18.6 degrees north and south, and then the Moon rises and sets on every day in Tromsø and Reykjavik except the usual 12 or 13: no whole days up or down at all, and no spell longer than 0.9 days. See the Moon's 18.6-year cycle.

How These Times Are Computed

Moonrise and moonset here are the moments the top edge of the Moon touches a flat, sea-level horizon, with the standard allowance of 34 arcminutes for atmospheric refraction and with the Moon's parallax, as seen from the city centre. Days are calendar days of each city's legal time zone, midnight to midnight, so London, New York and Tromsø follow their summer time. Published almanacs may differ by a minute or so if they use other conventions.

A real horizon changes the details. A hill or a building to the east delays moonrise by minutes; see why altitude and terrain matter. When the night's moonrise is within a few minutes of midnight, as in Mecca at 23:55 on 23 September 2027, that is enough to move the day without a moonrise by one day for an observer with a raised horizon.

Frequently Asked Questions

Does the Moon rise every day?

No. Because each moonrise is on average 50.5 minutes later than the one before, there are only about 353 moonrises in a year of 365 days. On the remaining 12 or 13 days, about one per lunar month, the Moon does not rise at all by the local calendar. At high latitudes there are many more such days.

Why is there no moonrise today?

Most likely the Moon rose late last night, before midnight, and will next rise early tomorrow, after midnight, so today is skipped. This happens near the last quarter. In Mecca in 2027 it falls within 1.7 days of the last quarter every month.

Is the Moon visible on a day with no moonrise?

Often, yes. The Moon rose the night before and is still up in the morning: on 24 September 2027 in Mecca it stays above the horizon until 13:53. The evening is the part of the day without a Moon.

Does a day without moonrise affect the Islamic date?

No. The Hijri month begins with the crescent after the new moon, and the Islamic day begins at sunset. A day without a moonrise is a feature of the civil, midnight-to-midnight calendar. By the Umm al-Qura calendar, Mecca's days without a moonrise in 2027 fall on the 20th to 23rd of the month.

Where can I check moonrise for my place?

The Moon page gives the day's moonrise and moonset for your location and date, along with the phase and the Moon's age.

See Also

• Why the Moon's path across the sky changes every month
• The four kinds of lunar month
• The Moon's 18.6-year cycle and the crescent
• When the Moon stands over the Kaaba
• Supermoon, blue moon, micromoon
• The Moon page for moonrise, moonset and the phase, and the Hijri calendar.

References

• Moonrise, moonset, phases and declinations are computed with the astronomy engine of this site, as seen from each city with standard refraction and parallax. The numbers are reproduced by docs/research/moonrise.mjs and computed by packages/astronomy/src/moonRiseSet.ts in the Hilal Vision source; Umm al-Qura dates come from the @umalqura/core table used across the site.
• Cross, D. astronomy-engine, the open source astronomy library behind these rise and set times (function SearchRiseSet). https://github.com/cosinekitty/astronomy
• Meeus, J. (1998). Astronomical Algorithms (2nd ed.). Willmann-Bell. Chapter 15, rising, transit and setting.