The Easter Full Moon.

Easter Moon.

Image: Courtesy of Pixabay.

The Moon is our nearest neighbour, and many people do not realise what a fascinating world it is. Its phases are also linked to the date of Easter, although not in a simple way!

The commonly stated rule that Easter is the first Sunday after the first Full Moon following the vernal or spring equinox is not quite correct. Strictly speaking, these days, Easter is the first Sunday following the "Ecclesiastical Full Moon" date after March 20th. Rather confusingly, the date of the Ecclesiastical Full Moon is determined from tables, and it may differ from the date of the real Full Moon by up to two days. This is because in June 325 AD, astronomers decided to approximate the true full moon dates for the Christian church, calling them Ecclesiastical Full Moons. Incidentally, March 20th was the date of the equinox in 325 AD.

The possible dates for the relevant Ecclesiastical Full Moon, (known as the Paschal Full Moon), are March 21 through April 18. This gives a range of dates for Easter Sunday extending from March 27 through to April 24. Note that if the Ecclesiastical Full Moon falls on a Sunday, Easter is the following Sunday.

Even with the naked eye, you can see bright regions and darker patches on the Moon. Use binoculars or a telescope and you will see a tremendous amount of detail. The large, dark plains are called 'seas', but there has never been any water in them.

Explore the Moon with us at the Planetarium - it's a rugged little world with mountains, valleys, and a vast number of circular walled structures called craters. Learn about the phases of the Moon, how it raises the ocean tides, how it regulates Earth's climate, and how it is slowly making our day longer.

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