A full moon hasn't risen on the solstice in decades.
Look up at the sky tonight, and you will see a rare celestial phenomenon: a solstice full moon. Depending on your time zone, it may be the first since 1948.
The June solstice, observed at 6:34 p.m. ET, when the sun reaches its northernmost position in the sky, will mark the first day of summer, and the longest day of the year. (Of course it's a Monday!) Then, as the sun sets two hours later, a full moon will rise in the east.
June's full moon is known as the strawberry moon because it appears at the peak of strawberry season. Algonquin tribes considered it a signal to start harvesting the fruit, according to the Farmer's Almanac. But tonight's full moon may mean other things aside from perfectly ripe berries. Research suggests it might affect us in a handful of unexpected ways.
If you've been sleeping fitfully, for example, this lunar phase could be to blame. In a 2013 study published in the journal Current Biology, researchers found that on nights surrounding a full moon, participants had lower levels of the sleep hormone melatonin. They also slept 20 fewer minutes overall, and brain activity related to deep sleep declined 30%.
Research has also hinted there may be a link between the lunar cycle and a woman's menstrual cycle. According to a 2011 study in the journal Acta Obstetricia et Gynecologica Scandinavica, some women's periods may be synced to the full moon. The researchers found that of the 826 women who participated in the study, 30% had their period during the full moon.
The moon may even have an effect on surgical outcomes. A 2013 study revealed that people who had emergency heart surgery during a full moon were less likely to die. They also spent, on average, four fewer days in the hospital than patients who underwent the same surgery during two other moon phases.
But whether you notice any effects from tonight's moon or not, you're likely to feel good this week. As TIME reports, the summer solstice may be the happiest day of the year, possibly due to the extra minutes of sunlight; or because during the summer, our natural circadian rhythms become more closely aligned with the 24-hour cycle of sunlight and darkness, which can influence both our sleep and our moods.
Now go soak up some extra rays, and make sure you hang out long enough to catch a glimpse of a beautiful moon.