On 30 August 2023, a super blue moon lit up the night sky with a bold and bright face, appearing around 14% larger than usual. The photographs captured from across the world were spectacular as it rose above Earthlings, from a baseball game in San Francisco to the famous Galata Tower in Istanbul, Turkey.

What makes a super blue moon so special is that it is really a trifecta of phenomena all occurring in one, dazzling lunar event — a full moon, a supermoon and a blue moon all coinciding. 

Brandon Williamson of the Cincinnati Reds pitches against the San Francisco Giants while an almost full moon rises behind him in the fourth inning at Oracle Park on 29 August, 2023 in San Francisco, California. (Photo: Ezra Shaw/Getty Images)

Firstly, a full moon occurs when the moon is directly opposite the sun with the Earth in between. Here, the sun reflects off of the moon’s surface and beams to Earth. As the moon orbits Earth, it stands at different angles to the sun, appearing to be in different phases. The moon takes about 27.3 days to complete a revolution around the Earth. 

A full Blue Moon rises over El Pilar Basilica in Zaragoza, Spain on 30 August 2023. (Photo: EPA-EFE/Javier Belver)

However, the moon does not orbit around the Earth in a perfect circle. Rather, the moon travels in an elliptical fashion around the Earth, which is always closer to one end of the ellipse, never directly in the middle. This means that at times the moon will be closer to the Earth on one end of the elongated circle than it is at the other side. When the Moon is at the closest point to Earth at the same time that it is full, a supermoon is occurring, where it appears closer, larger and brighter in the sky. In 2023, four out of the 13 full moons are supermoons. 

Finally, a blue moon is a term that refers to the occurrence of two full moons in the same month. The moon is not actually blue, but the phrase does inform the idiom “once in a blue moon”, where an event happens very rarely. A blue moon occurs because the moon’s orbit is slightly less than a full month, so every once in a while, two full moons will take place within the same month. 2023 only saw one blue moon, making the August 30 event even more significant. This definition has been around since 1946, but an older definition has been around since the 1500s, which referred to the third full Moon in a season that has four Moons. 

The closest full moon this year, and a super blue moon on 30 August, 2023 in Johannesburg, South Africa. (Photo: Gallo Images/Dino Lloyd)

When these three moons occur together, it makes for a particularly rare event. According to Nasa, about 25% of all full moons are supermoons, but only 3% of full moons are blue moons, and the next super blue moons will only occur again in January 2037. 

Tidal warnings

The super blue moon was more than a pretty face, and prior to its occurrence, coastal authorities issued notices warning communities to be cautious.

“This full moon brings the Spring tide — where high tide is higher than normal and low tide is lower than normal,” the National Sea Rescue Institute said. 

“Spring tides occur at full moon and at new moon every month [and] can have an increased effect on the strength of rip currents.” 

A full blue moon rises behind the San Francisco skyline on 30 August, 2023 in San Francisco, California. The next super blue moon will not appear until 2037. (Photo: Justin Sullivan/Getty Images)

Tides are caused by the moon’s gravitational pull on the Earth, changing the distribution of the oceans. As the moon orbits, the gravitational forces draw the Earth’s water and create tides. When the moon is full, the Earth, Sun, and Moon line up and their gravitational power combines to make exceptionally high tides, called spring tides, as well as very low tides where the water has been displaced. In the United States, the Spring tides could not have come at a worse time, as Hurricane Idalia battered Florida’s coasts and the tides exacerbated flooding from the storm.

A rare super blue moon appears in the night sky over Ben Buckler Cliffs at Bondi Beach in Sydney, Australia, 31 August, 2023. (Photo: EPA-EFE/Dan Himbrechts)

Shining down on Earth

From the Jewish calendar to the Chinese calendar, the moon has played a central role in various religions and cultures for centuries. 

This year, the super blue moon also corresponded with the Hindu festival Raksha Bandhan, which honours the bond between brothers and sisters. To celebrate, siblings tie rakhi, a sacred thread, around each other’s wrists and exchange gifts. DM