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Blue moon to appear tonight
今晚将出现蓝月亮
A blue moon is generally understood to be second full moon in a month, a phenomenon that won’t happen again until 2018. But the moon won't look blue.
一般来说，人们认为蓝月亮是每个月的第二次满月，这种现象直到2018年才会出现。然而，蓝月亮并非蓝色。
Look out into the sky after midnight tonight, and you will be able to sneak a peek at a “once-in-a-blue-moon” phenomenon: A blue moon, itself.
今晚午夜仰望天空，大家将看到一种千载难逢的现象：蓝月亮。
The “blue” moon will be visible on Friday. Its appearance marks the second full moon in the month of July, a phenomenon that won’t happen again until 2018.
本周五将出现“蓝”月亮。标志着7月的第二次满月，这种现象直到2018年才会出现。
But what exactly does a blue moon look like, and is it really all that rare? What is a blue moon?
然而，蓝月亮到底是什么样的？真的那么罕见吗？什么是蓝月亮？
When two full moons fall within the same calendar month, that second moon is called a blue moon. The first full moon this month was seen on July 2.
如果在同一日历月内出现两次满月，则称第二次满月为蓝月亮。本月第一次满月出现在7月2日。
“It’s basically because a lunation is 29-and-a-half days . . . that you wind up having a second full moon in a calendar month,” explained Paul Mortfield of The David Dunlap Observatory in Richmond Hill.
“基本是因为阴历月有29天半，因此，只在日历月内存在第二次满月，” 列治文山大卫邓拉普天文台的Paul Mortfield解释道。
“All it is, is an extra full moon that we get, and that’s been going on for millennia,” Mortfield told the Star.
“蓝月亮是额外的满月，已经持续了千年，”Mortfield告诉《星报》。
Confusingly, the term “blue moon” can also be used to describe the third of four full moons that occur in a single season.
令人困惑的是，如果一个季度中出现四次满月，“蓝月亮”一词也可用来描述其中的第三次满月。
Where does the definition come from?
此定义从何而来呢？
NASA says the original definition of a blue moon, detailed in the Maine Farmer’s Almanac, was “so convoluted many astronomers struggled to understand it.”
美国航空航天局称，《缅因州农夫年历》详细介绍了蓝月亮的原定义，“非常复杂，以至于很多天文学家都难以理解。”
A 1946 article in Sky & Telescope magazine, however, redefined the term blue moon as a “second (full moon) in a month.”
然而，1946年在天空&望远镜杂志上刊登的一篇文章重新将蓝月亮一词定义为“每月的第二次满月。”
Although this was a mistake, the definition stuck, and we have come to use it that way ever since.
尽管这一定义是错误的，人们却从那时起就这样理解蓝月亮。
How often do blue moons occur?
蓝月亮多久出现一次？
Two full moons generally appear in the same month once every two or three years: the last occurrence was in August 2012, and the next one is expected in January 2018.
一般来说，每两年或三年在同一月内出现两次满月：上次发生在2012年8月，预计下一次将出现在2018年1月。
The second type of blue moon, the third of four full moons in a season, happens every three years or so. The last was in 2010, and the next one is expected in May 2016.
第二类蓝月亮，即如果一个季度中出现四次满月，则为第三次满月，大约每三年出现一次。
译文属可可英语原创，未经允许，不得转载。
