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Supermoon: Biggest, brightest moon to light up night sky on Sunday

SF Gate logo SF Gate 11/29/2017 Amy Graff

@jeremyborkat captured the Supermoon rising over the Marin Headlands.

@jeremyborkat captured the Supermoon rising over the Marin Headlands.
© @jeremyborkat / Instagram

You'll want to take a moment to step outside on Sunday night and look up into the nighttime sky.

The biggest, brightest moon of 2017 will light up the sky on Dec. 3.

The so-called "supermoon" occurs when the moon is close to what we call "perigee" in scientific terms, the point when the moon is closest to the earth in its orbit,"

"The moon will appear up to 14 percent larger than it would appear if it was at its most distant point," says Gerald McKeegan, an astronomer at the Chabot Space and Science Center in Oakland.

The science center will host its weekly Friday and Saturday night viewing, staying open until 10:30 p.m., and McKeegan says, "If people want to come up and look at the full-moon that's a good time to do it if the weather is right."

If you can't make it to the center, the best time to view the moon, McKeegan says, is when the moon is rising or setting as an optical illusion makes the moon appear even larger than normal when it's on the horizon.

Supermoons are common, happening about once a year (though two more are coming in January 2018), and McKeegan says astronomers typically don't get excited about them. But last year, the supermoon gained a lot of attention as the moon was the closest it had been to earth since January 1948.

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