Why 2027 Has 13 New Moons but Only 12 Full Moons

A new moon is the moment the Moon passes between Earth and the Sun. Its lit side faces away from us, so for a night or two there is nothing to see. A full moon is the opposite moment, when Earth sits between the two and the whole face we see is lit. Astrologers call each of these moments a lunation, and they treat the new moon as the start of a lunar month and the full moon as its peak.

The time from one new moon to the next is the synodic month. NASA gives its average as 29.53059 days, or 29 days, 12 hours and 44 minutes. That is longer than the 27.3 days the Moon takes to circle Earth once against the stars, because Earth is also moving around the Sun. Each month the Moon has to travel about two extra days to line up with the Sun again.

The average hides a wobble. The Moon's orbit is an ellipse and so is Earth's, so the real gap between new moons stretches and shrinks. In 2027 the shortest gap is 29.29 days and the longest 29.81, a swing of more than twelve hours. Our new moon calendar for 2027 lists every one of them with its time and sign.

Twelve lunar months add up to 354.37 days. A calendar year has 365, or 366 in a leap year. So every year the phases of the Moon fall about 11 days earlier on the calendar than they did the year before.

That slide is the whole story. Most years, the first new moon lands somewhere in the middle of January and twelve new moons fit before the year runs out. When the first one lands in the first 10 or 11 days, a thirteenth squeezes in at the end. In 2027 the first new moon falls on January 7 and the thirteenth on December 27.

The full moons sit about two weeks out of step with the new moons, so they miss. The first full moon of 2027 is on January 22 and the last on December 13. The next one after that is January 12, 2028, which is why 2028 swings back the other way and holds 13 full moons, the last of them a Blue Moon on December 31. 2026 had 13 full moons too: the extra one in 2026 was the Blue Moon of May 31.

A calendar built on the Moon runs straight into this problem, and people who kept one solved it by adding a month.

The Hebrew calendar is the best known case that is still in daily use. It counts lunar months but keeps Passover in spring by adding a thirteenth month in seven years out of every nineteen. Without that extra month the festival would drift through the seasons, about 11 days a year, exactly the gap this story is about.

The early English did the same. Writing in 725, the monk Bede described the months of the pagan English year in his book The Reckoning of Time. The word for month, monath, came from mona, the Moon. In a year with 13 lunar months the extra one went into summer, and that year had its own name, Thrilithi, a year with three months called Litha.

Our own Gregorian calendar went the other way. Its months ignore the Moon entirely, which is why a full moon can fall on any date and why the folk names of the full moons, covered in How the Moon Got Its Folk Names, only loosely fit the months they are pinned to.

The ninth new moon of 2027 happens at a single instant: August 31 at 17:41 UTC. Where you are on Earth decides what the calendar says at that instant.

In New York it is 1:41 pm on August 31. In London it is 6:41 pm and in Mumbai 11:11 pm, still August 31. So in the Americas, Europe, Africa and India, August holds two new moons, on the 2nd and the 31st. In popular astrology the second new moon in a calendar month is called a Black Moon, the new moon twin of the better known Blue Moon.

In Bangkok the same moment is 12:41 am on September 1. In Tokyo it is 2:41 am, in Sydney 3:41 am. Across East Asia and Australia, August keeps one new moon and September gets two, on the 1st and the 30th. Same sky, same year, same count of 13, but the Black Moon lands in a different month.

In Western astrology each new moon is read as a starting point, the dark of the cycle before the light returns. Many astrologers describe a year as a run of lunar chapters rather than twelve calendar months, and a 13-lunation year simply has one more chapter.

The extra new moon of 2027 is a striking one. The Black Moon of August 31 falls at 8 degrees of Virgo, within a third of a degree of Jupiter, with the Sun, Mercury and Venus in the same sign. Astrologers read a new moon joined to Jupiter as a beginning with room to grow, and a sign this crowded as a theme that fills the sky. The story of that line-up, and how rare five bodies in one sign really is, is in Five Planets in Virgo.

None of this changes the arithmetic. The extra new moon arrives because 29.53 does not divide 365, and the Black Moon's month depends on a time zone border. What a reader makes of it is a question of reflection, not of fate.

For the full moons of the same year, with their dates and names, see the full moon calendar for 2027, and for every other date of the year the 2027 astrology calendar. The two solar eclipses of 2027, including the long total eclipse of August 2, are both new moons too: the story of that one is The August 2, 2027 Eclipse. To see which house of your own chart each new moon falls in, cast your free birth chart.