Update: According to the National Weather Service, Portland area residents will see cloudy skies overnight, but they won't be very dense. There should be enough breaks in the sky to catch the full moon, said Liana Brackett, meteorologist.

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It's not a supermoon, but for the first time since 1977 a full moon will grace the Christmas sky.

That was the year the Trailblazers won the NBA championship, Jimmy Carter was in the White House and the Yankees beat the Dodgers in the World Series. A movie called "Star Wars" hit theaters.



The moon reaches its peak at 3:11 a.m. Christmas day. According to the Star Date stargazing website, the December full moon is known as a Full Cold Moon, Full Long Nights Moon or the Moon Before Yule.



NASA scientists say the next chance for a full moon on Christmas won't come around until 2034, 19 years away. And just in time for the 10th or 11th "Star Wars" movie.



And while we're on the subject, you think you know the Moon? NASA has a list of common misconceptions about our neighbor:



Misconception: Phases of the Moon are caused by a shadow from the Earth, clouds, or the Earth's or Moon's rotation.

Reality: Our perspective of the Moon's sunlit appearance changes as it orbits Earth.



Misconception: Different countries see different phases of the Moon on the same day.

Reality: Everyone sees the same phases of the Moon, but people south of the equator who face North to see the Moon when it is high in the sky will see the Moon upside down so that the reverse side is lit.



Misconception: The Moon goes around the Earth in a single day.

Reality: It takes about a month for the Moon to orbit Earth (27.3 days to complete a revolution, but 29.5 days to change from New Moon to New Moon).



Misconception: The Moon makes its own light (the same way the Sun does).

Reality: The Moon reflects the light of the Sun, just as the planets do. In fact, the bright part of the Moon is experiencing daytime.



Misconception: The Moon does not rotate.

Reality: The Moon does spin on its axis, completing a rotation once every 27.3 days; the confusion is caused because it also takes the same period to orbit the Earth, so that it keeps the same side facing us.



Misconception: The same half of the Moon is in darkness all the time-i.e. that there is a dark side of the Moon.

Reality: The Moon has no side that is constantly dark; the front and back are alternately lit as the Moon rotates. Far side is a more accurate term.



Misconception: The Moon has no gravity; things float "up" when dropped on the Moon.

Reality: The Moon does have gravity, but because it has less mass than the Earth, it has 1/6 of Earth's gravity at its surface.



Misconception: The Moon is only visible at night.

Reality: We frequently see the Moon in the day; the only phases of the Moon that cannot be seen in the day are full moon (which is usually only visible at night) and the new moon (which is not visible from Earth at all).



Misconception: The Moon becomes larger on the horizon because it is closer to Earth.

Reality: This is an optical illusion. For reasons not fully understood by astronomers or psychologists, low-hanging moons look unnaturally large when they beam through trees, building or other foreground objects.

-- Stuart Tomlinson

stomlinson@oregonian.com

503-221-8313

@ORweather