The Short Answer
We took every eclipse from 2024 to 2035, 53 in all, and asked which day of the Umm al-Qura month each one falls on. The pattern is strong:
- Solar eclipses land on the 28th, 29th or 30th, and 20 of the 26 land on the 29th.
- Lunar eclipses land on the 13th, 14th or 15th, and 24 of the 27 land on the 14th or 15th.
This is not a coincidence, and it is not a feature of the Umm al-Qura tables. It is a direct consequence of what the two kinds of eclipse are. A solar eclipse can only happen at the new moon, the conjunction of Sun and Moon. A lunar eclipse can only happen at the full moon. Islamic months are built around the new moon, so a solar eclipse falls where the month ends and the next one is about to begin: on the very day the new crescent, the hilal, is hunted.
What We Counted
The eclipse instants come from the same astronomy engine that drives the eclipse tracker and the crescent visibility map. We took the moment of greatest eclipse for each one, found the calendar date in Riyadh at that moment, and read off the Umm al-Qura day of the month from the same calendar table that powers the calendar page.
| Umm al-Qura day | Solar eclipses (26) | Lunar eclipses (27) |
|---|---|---|
| 13th | 0 | 3 |
| 14th | 0 | 12 |
| 15th | 0 | 12 |
| 28th | 2 | 0 |
| 29th | 20 | 0 |
| 30th | 4 | 0 |
Nothing in either column lands outside its narrow band. Across twelve years and 53 events, no solar eclipse falls between the 1st and the 27th, and no lunar eclipse falls outside the 13th to 15th.
Why the Solar Eclipse Lands on the 29th
Start from the Moon's cycle. Once a lunation (the synodic month, about 29.5 days) the Moon passes between Earth and Sun. That moment is the conjunction, and it is the astronomical start of a new lunation. A solar eclipse is simply a conjunction that happens close enough to the plane of Earth's orbit for the Moon's shadow to touch Earth. The greatest eclipse comes within a fraction of an hour of the conjunction itself.
Now the calendar. The Umm al-Qura rule, in use since 1423 AH, starts a new month on the evening of the 29th if the conjunction has happened before sunset in Mecca and the Moon sets after the Sun there. Otherwise the month runs to 30 days. (The Umm al-Qura explainer has the details, and the reasons the rule does not guarantee a visible crescent.) Either way, the new month is anchored to the conjunction, and the conjunction falls at the end of the old month, in the last two or three days.
The 29th is the centre of that window, because it is the day the rule is tested. If the conjunction came earlier that day, the month can end after 29 days. If it came later, or the Moon sets too early, the month takes a 30th day. So a solar eclipse, which marks the conjunction, tends to sit on the 29th, with the 28th and 30th as the shoulders.
The same arithmetic works for the lunar eclipse. A full moon comes about 14.8 days after the new moon. If the month begins on the evening after conjunction, the full moon falls around the 14th or 15th. That is why the lunar eclipses cluster there.
The two kinds of eclipse are also linked to each other in time, a story told in why eclipses come in pairs: a solar eclipse near the end of one month is usually followed, about two weeks later, by a lunar eclipse in the middle of the next.
The Day Number Depends on When You Start Counting
There is a subtlety that matters for anyone who reads the table above carefully. The Umm al-Qura calendar, like the civil calendar everywhere, changes date at midnight. The Islamic day, by contrast, begins at sunset. The evening of the 29th, after sunset, is already the 30th by Islamic reckoning.
So the numbers above are calendar dates on the Riyadh clock. If we instead count the Islamic day, an eclipse whose greatest moment falls after sunset in Mecca moves to the next day number. Here are both versions, using Mecca's sunset:
| Convention | Solar eclipses (26) | Lunar eclipses (27) |
|---|---|---|
| Calendar date (midnight rollover) | 28th: 2, 29th: 20, 30th: 4 | 13th: 3, 14th: 12, 15th: 12 |
| Islamic day (begins at Mecca sunset) | 28th: 1, 29th: 12, 30th: 13 | 14th: 13, 15th: 12, 16th: 2 |
Both columns of the figure are drawn together: solid bars for the calendar date, outlined bars for the Islamic day.
Three things follow.
First, the claim "solar eclipses fall on the 29th" is true of the calendar date, and only partly true of the Islamic day. Counted from sunset, the solar eclipses split almost evenly between the 29th and the 30th, depending on whether the Moon passes the Sun before or after Mecca's evening. The band is still just a few days wide, and it still sits at the end of the month. The honest statement is that a solar eclipse falls on the last days of the month, most often on the day the crescent is hunted.
Second, the solar eclipse is a global event with no single local time. The greatest eclipse happens at one instant, but the sky over Riyadh may be in full daylight or deep night when it does. For example, the total eclipse of 8 April 2024 peaked at 18:17 UTC, which is 21:17 in Riyadh, long after dark there, while it was around midday over Mexico. We fixed the clock on Riyadh and Mecca because that is where the calendar is defined, but a reader in another time zone could put the same eclipse on an adjacent date.
Third, the lunar band shifts by a day. On the Islamic count the lunar eclipses fall on the 14th, 15th and, twice, the 16th. We therefore state the lunar result as a band around the middle of the month, "about the 14th to the 15th", and mean the calendar date, not the Islamic night.
A Caveat About the Calendar Table
The Umm al-Qura calendar is computed in advance, so dates in the 2030s are projections made by software, not announcements. We used the Umm al-Qura table inside the library that powers the calendar page. For 2024 to 2028 the result is clean: all ten solar eclipses fall on the 29th. From 2029 onward the table we use and the one built into JavaScript's Intl calendar disagree by one day on some dates, and a count made with Intl gives 21 of 26 on the 29th rather than 20. The conclusion is the same under both. The exact tally for the later years is the least certain part of the table.
The Example We Can Check Today: 6 February 2027
The annular eclipse of 6 February 2027 sits on exactly this fault line. The calendar date is the 29th of Shaban 1448, and the Umm al-Qura calendar puts the first day of Ramadan on Monday 8 February. Greatest eclipse is at 15:59 UTC, which is 18:59 in Mecca, after sunset there, so by the Islamic count the eclipse belongs to the 30th. The new moon itself is at 15:56 UTC, three minutes before greatest eclipse and 43 minutes after Mecca's sunset. That is the evening on which the hilal is searched for. As that post explains, the Moon is not yet new at sunset in Arabia, so no crescent can be seen from there that evening. Shaban completes 30 days.
One date, two ways of counting: the 29th on the calendar, the 30th by sunset. Both are correct.
What This Means in Practice
A few practical consequences:
- An upcoming solar eclipse tells you the day of the new moon. When the eclipse tracker lists a solar eclipse, the conjunction is on that date, which puts it at the end of a Hijri month and makes it a good moment to look at the crescent forecast.
- The eclipse does not change whether the crescent is visible. It tells you exactly when the conjunction is. Whether the crescent can then be seen depends on the Moon's age and its position relative to the Sun at the observer's sunset, which the visibility map shows with the Yallop and Odeh criteria.
- Check the date you mean. If you read that an eclipse falls on "the 29th", ask whether the date changes at midnight or at sunset.
Frequently Asked Questions
Is a solar eclipse always on the 29th of the Hijri month?
Almost always, on the calendar date. In our 2024 to 2035 count, 20 of 26 fall on the 29th, 2 on the 28th and 4 on the 30th. It is always within the last three days of the month, because a solar eclipse can only happen at a conjunction.
Why are lunar eclipses in the middle of the month?
A lunar eclipse needs a full moon, which comes about half a lunation, roughly 14.8 days, after the new moon. Months start close to the new moon, so the full moon falls around the 14th to the 15th.
Does the eclipse affect when Ramadan or another month starts?
No. The eclipse marks the conjunction, which the calendar rules already use. It does not change the Moon's visibility. The start of a month still depends on the rule or the sighting practice a community follows. See how the Umm al-Qura calendar works.
Would the pattern hold with a different calendar?
Any month that starts near the new moon will put solar eclipses near its end and lunar eclipses near its middle. Only the day numbers shift with the rule. We computed the numbers here for Umm al-Qura only.
Why does the count change when the day starts at sunset?
Because the evening of the 29th belongs to the next Islamic day. An eclipse whose peak falls after sunset in Mecca moves up by one. Counted that way, 12 of the 26 solar eclipses are on the 29th and 13 on the 30th.
See Also
- When Will Totality Return to Mecca? The Next Total Eclipses Over the Holy Cities
- Will I See the Lunar Eclipse? Every Lunar Eclipse to 2030, from London to Jakarta
References
- van Gent, R. H. The Umm al-Qura Calendar of Saudi Arabia. Utrecht University. https://webspace.science.uu.nl/~gent0113/islam/ummalqura_rules.htm
- Cross, D. astronomy-engine, the open source astronomy library behind the eclipse times and sunset times used here. https://github.com/cosinekitty/astronomy
Clear skies and happy sighting.