Technology & Science

See a summer solstice full moon for the 1st time in decades

Today is the longest day of the year, the summer solstice, and for the first time in decades, you can end it with a view of the full moon.

How many decades? It's complicated, but we're glad you asked

A full moon rises in Little Rock, Calif., on June 22, 2013. This year, June's full moon takes place on June 20, the same day as the summer solstice. (Gene Blevins/Reuters)

Today is the longest day of the year, the summer solstice, and for the first time in decades, you can end it with a view of the full moon.

Technically, the summer solstice isn't the entire day, but the moment when the Earth's northern axis of rotation is most tilted toward the sun — this year, that happens at 6:34 p.m. ET on June 20.

And technically, the moon was fullest at 7:02 a.m. ET, putting the two events on the same day.

How many decades it's been since that last happened depends on what time zone you're in — the last time it happened for those in Western and Central Canada was in 1986, 30 years ago, but those in Atlantic Canada haven't had a summer solstice full moon since 1967, according to J. Randy Attwood, executive director of the Royal Astronomical Society of Canada.

That's because the 1986 full moon occurred at 11:42 p.m. on June 21 — the day of the solstice — in Toronto, but 12:42 a.m. the next day in Halifax, the day after the solstice.

June's full moon is often called the "strawberry moon," a name believed to originate with Algonquin tribes who used it to mark the start of strawberry season.

The full moon rises over the temple of Poseidon, the ancient Greek god of the seas, in Cape Sounion some 60 kilometres east of Athens, on June 23, 2013. This June, the moon was technically fullest at 7:02 a.m. ET, 13½ hours before the summer solstice. (Yannis Behrakis/Reuters)

Typically, full moons fall equally often on every day of the year, but it's relatively rare for full moons to fall on any one day, such as June 21 or your birthday or Christmas. In Canada, this past Christmas was the first Christmas full moon since 1977.

The moon becomes full every 29.5 days, or 12 to 13 times a year. But because the moon's cycle doesn't divide evenly into the number of days in our calendar year, the full moon(s) for a given month is shifted about 11 or 12 days per year.

Extra complications arise because of time zone differences (as explained earlier), the fact that the moon is technically "fullest" at a particular time of day that varies, and the day and time of the summer solstice varies from year to year – it can happen on June 20, 21 or 22.

People ride the Luna Park Swing Ride as the full moon rises on Coney Island in New York, on June 22, 2013. The moon becomes full every 29½ days, or 12 to 13 times a year. (Carlo Allegri/Reuters)

That's because the summer solstice is technically the moment when the Earth's northern axis of rotation is most tilted toward the sun, and that happens every 365¼ days, and our calendar is just 365 days (with a leap year every four years) so the alignment between the two events varies, says Paul Mortfield, chair of the David Dunlap Observatory in Richmond Hill, Ont.

Likewise, the time when the moon is fullest can vary. Today's full moon is technically fullest at 7:02 a.m. ET – after it has set and no longer visible in Canada. By the time it rises again, it will have waned a bit. In fact, Sunday night's full moon (the night before the summer solstice) is fuller than Monday's night's. But don't let that ruin your enjoyment of the summer solstice full moon because the difference will be subtle, Mortfield says.

"For most people who will go out and look with their eyes, they'll see a full moon."

The last time the summer solstice and full moon were extremely closely aligned was in 1948, when the full moon occurred just 43 minutes after the summer solstice, according to the Royal Astronomical Society,

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