Statewide, the weather is expected to cooperate, so California's skywatchers will get a rare look at a blue moon this weekend. This second full moon in one month is named for the calendar rather than its color. A blue moon occurs when there is a second full moon in a single calendar month.
May 1st marked the first of this month's two full moons.
If you want to get out and see the second May full moon at its peak, head outside at 1:45 a.m. PST Sunday, May 31.
The weekend weather forecast for Southern California looks like clear early morning skies for the big event.
Despite the name, the moon won’t actually appear blue, according to NASA. It may look golden, orange or reddish when it is low on the horizon, the same effect that can make sunrises and sunsets appear warm-colored.
A truly blue-looking moon isn’t unheard of, and is usually caused by particles in the atmosphere, such as smoke or volcanic ash
Here’s another caveat: Far-northern skywatchers may also be entering the noctilucent cloud season. The high-altitude clouds can glow silver or electric blue after sunset or before sunrise, especially near the summer solstice, but they are unrelated to the blue moon and won’t make the moon itself appear blue.
The best time to see the moon will likely be around moonrise Saturday evening, May 30, when it climbs above the eastern horizon shortly after sunset. The moon will appear full to most casual observers from Saturday night into Monday.
This month’s blue moon is also a micromoon, which is the opposite of a supermoon. A micromoon occurs when the moon is near apogee, its farthest point from Earth in its orbit. A supermoon occurs when it is at perigee, making its closest approach to Earth in its elliptical orbit.
As a micromoon, this full moon will appear slightly smaller and less luminous than usual, though the variation may be subtle enough that casual observers would need a side-by-side comparison to notice the distinction.
The blue moon can be seen without a telescope. Binoculars can help bring out surface details, but the full moon is bright enough to see with the naked eye.
Pick a site with an open view of the eastern horizon and check local moonrise times.
Blue moons are uncommon but not extraordinary. They happen because the lunar cycle is about 29.5 days, while most calendar months are 30 or 31 days long. That mismatch occasionally gives a month two full moons.
A less common definition calls the third full moon in a season with four full moons a blue moon. By that measure, the next blue moon will occur May 20, 2027.
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