A Midsummer Night’s Moon

Midsummer or Midsommar is a traditional Scandinavian festival celebrating the summer solstice. This year’s Midsummer night is lit by a Full Moon, a rare treat and a great reason to celebrate both astronomical events.

The solstice celebration is closely linked to the Christian feast of St. John the Baptist, celebrated on June 24th. Many traditional summer festivities in Northern Europe have been Christianized and named after St. John, or Sankt Johannes (Juhannus, Hans, Jani) in the local languages (see table).

Solstice and Moon Phases: Connected Astronomical Events?

When astronomical events coincide, it can be magical: Jupiter and Saturn dance closely in the night sky, or the Moon totally eclipses the Sun. But what about the solstice? Is it also connected to the Moon phase in some way?

“It’s just a coincidence that, this year, June’s Full Moon falls close to the solstice,” says Graham Jones, astrophysicist at timeanddate.com. “But it’s really fun to spot these astronomical coincidences. For example, there’s the Metonic cycle, where—by chance—Full Moons and other lunar phases occur on roughly the same calendar dates every 19 years.”

Full Moon Holidays: Accident or Design?

How rare are holidays that fall on a Full Moon? We had a closer look at our holiday database with over 7000 holidays and found that in 2024, only 5.9% fall on a Full Moon night. And only one holiday celebrates the summer solstice under the Strawberry Moon: Midsummer or St. John’s Feast.

417 out of 7051 holidays in the timeanddate.com database coincide with a Full Moon* in 2024. Out of the 417 Full Moon holidays, 290 are accidental (69.5%), the rest are actually designed to fall on a Full Moon.

An accidental Full Moon holiday is a holiday or observance with a fixed date, such as Juneteenth, that happens to coincide with a Full Moon phase in a given year. Here are three such Full Moon holidays in 2024:

1. Midsummer in Finland (June 22, 2024)

   The celebrations involve lighting bonfires, which are symbols meant to ward off evil spirits and ensure a good harvest. Traditional activities include sauna sessions followed by swims in nearby waters, feasting on pickled herring, new potatoes, and grilled foods, and enjoying the nearly continuous daylight known as the Midnight Sun. Illumination: 99.8%**

2. Independence Day in Colombia (July 20, 2024)

   This national holiday commemorates Colombia’s declaration of independence from Spain. It is marked by parades, music, dance, and other festive events that continue into the night. The Full Moon on this night will illuminate the celebrations, adding to the joyous and vibrant atmosphere of the festivities. Illumination: 99.8%**

3. Crown Princess Mette-Marit’s Day in Norway (August 19, 2024)

   The birthday of the future Queen of Norway (born August 19, 1973) is neither a public holiday nor a common celebration in Norway. It is an official “flag day,” indicating official flagging on buildings and sites, but otherwise a normal day. This year, both Mette-Marit and her husband, Crown Prince Haakon of Norway, happen to both celebrate birthdays under a Full Moon. Illumination: 98.9%**

Designed Full Moon Holidays

30.5% of this year’s Full Moon holidays have consistently fallen on a Full Moon date for the last three years. These holidays seem like they have been designed to land on a Full Moon—because they are. Many religions celebrate important feast days and observances according to a lunar calendar; in other words, these days don’t have fixed dates in the Gregorian calendar, but a fixed Moon phase.

An example of a designed Full Moon holiday is the Poson Full Moon Poya Day in Sri Lanka on June 21, 2024. The Poson Festival (Poson Poya) celebrates the introduction of Buddhism to Sri Lanka during the third century BCE. It is one of the most important Buddhist festivals on the island, along with Vesak.

Finding Astronomical Holidays

At timeanddate.com, we’re passionate about astronomy and holidays. Since we offer data and services in both areas, we decided to have a look at the intersection of astronomy and culture in the form of astronomical holidays.

This article is based on our Astronomy data and our extensive Holiday database. Both services and data are available as APIs for developers and as (paid) data downloads on our API page.

* Astronomically, a Full Moon only lasts for a brief moment when the Moon lies opposite the Sun in the sky and is fully illuminated. Since this event lasts but a moment, only one day per month is marked as a Full Moon in the calendar. However, the Moon certainly looks like it is fully illuminated for several days. For the purposes of finding Full Moon holidays, we have thus broadened the definition of a Full Moon to any day with an illumination of at least 98%. This yields several Full Moon days per month, and allows us to include in our list many cultural celebrations tied to the Moon that astronomically do not fall on a Full Moon day, but the day before or after.

** Illumination: The percentage of the Moon’s surface that is lit by the Sun as seen from Earth.