Saturday, 31 March 2018

The Second Blue Moon of 2018

2018’s 2nd Blue Moon on March 31
We have a total of 8 Blue Moons in the upcoming 19-year Metonic cycle

Tonight – March 31, 2018 – that full moon you’ll see in the sky all night carries the name Blue Moon. In fact, it’s the second and final Blue Moon of this year. By popular acclaim, a Blue Moon is defined as the second of two full moons to occur in one calendar month. January had two full moons. Now March does, too.

Two Blue Moons in one year seem to belie idea that once in a Blue Moon indicates something rare. It’s true that, in recent years – with more than one definition for Blue Moon – Blue Moons seem to happen pretty often. Yet it’s indeed quite rare to have two Blue Moons in a single calendar year. It last happened in 1999 and won’t happen again until 2037.

A calendar year only embraces two Blue Moons if there are 13 full moons in one calendar year – and, in addition, February has no full moon at all. That’s exactly what happens in 2018. February didn’t have a full moon, while January and March both have two full moons. Thus – in 2018 – the full moons on January 31 and March 31 both count as Blue Moons.

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Saturday's Blue Moon Is the Last One Until 2020

The second New Moon in a single is called a 'Black Moon'

Skywatchers take note: The last Blue Moon of 2018 is just around the corner. If you miss it, you'll have to wait to 2020 for the next one.

The upcoming Blue Moon — the name given to the second full moon to occur in a single calendar month — rises on Saturday (March 31). It'll be the second Blue Moon of the year; the first occurred on Jan. 31, when we experienced the "Super Blue Blood Moon Lunar Eclipse."

If you're a Blue Moon fan, make sure to get an eyeful on Saturday; the next one won't come until Halloween night in 2020, according to the Weather Channel.

Blue Moons aren't actually blue, and they don't look different from any other full moon in the sky. The term, which has been around for hundreds of years, apparently originally signified something that's absurd, but then shifted over time to refer to exceedingly rare events, Philip Hiscock wrote in a 2012 article for Sky & Telescope. (Interestingly, a Blue Moon previously meant the third full moon in a season that had four of them. This sense of an "extra" full moon morphed into the definition most people recognize today. Language is a slippery and changeable thing!)

But Blue Moons aren't all that rare, really: On average, they occur about once every 2.7 years. Blue Moons are possible because it takes Earth's nearest neighbor 29.5 days to circle our planet, but each calendar month (except February) contains 30 or 31 days.

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When to See the (Blue) 'Sap Moon'

The month of March opens and closes with a full moon this year, making this the second "Blue Moon" month in 2018.

The moon first became full on Thursday, March 1, at 7:51 p.m. EST (0051 GMT) and will again on Saturday, March 31, at 8:37 a.m. EDT (1237 GMT). The first Blue Moon of 2018 was the spectacular Super Blue Blood Moon of Jan. 31.

Not every month gets two full moons. The time between full moons (known as a synodic month) averages 29.53 days, so we usually see one full moon per month. About every two to three years on average, we see a "Blue Moon" — a second full moon in one month.

Two Blue Moons in a year is relatively uncommon. According to, the next year when two calendar months will each have two full moons will be 2037, when January and March will have Blue Moons. The last time it happened was in 1999.

One effect of having a full moon on Jan. 31 and March 1 is that February has no full moon at all. February is the only month in which this can happen, because the month has only 28 days (while the phenomenon can happen in a leap year, it is rare). The next time a full moon will skip February will be in 2037, according to, a site run by amateur astronomers, and the phenomenon is sometimes referred to as a "Black Moon."

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2018 Full Moon Calendar

The moon shows its full face to Earth once a month. Well, sort of.

In fact, the same side of the moon always faces the planet, but part of it is in shadow. And, in reality most of the time the "full moon" is never perfectly full. Only when the moon, Earth and the sun are perfectly aligned is the moon 100 percent full, and that alignment produces a lunar eclipse. And sometimes — once in a blue moon — the moon is full twice in a month (or four times in a season, depending on which definition you prefer). [The Moon: 10 Surprising Facts]

The next full moon will be a Blue Moon — the second full moon of January — on Wednesday, Jan. 31. To casual observers, the moon will still appear full the day prior and after the peak. Like January's first full moon, the second full moon will be a "supermoon" as the moon arrives at perigee close to reaching its fullest phase. There will also be a total lunar eclipse during the Blue Moon, which some are billing as a rare Super Blue-Blood Moon Lunar Eclipse. Such a Blue Moon total lunar eclipse has not occurred for 152 years, our skywatching columnist Joe Rao has found.

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Full moon

The full Moon as viewed through a 235 mm (9.25 in) Schmidt-Cassegrain telescope. The Moon was near its northernmost ecliptic latitude, so the southern craters are especially prominent

The full moon is the lunar phase when the Moon appears fully illuminated from Earth's perspective. This occurs when Earth is located directly between the Sun and the Moon (more exactly, when the ecliptic longitudes of the Sun and Moon differ by 180°). This means that the lunar hemisphere facing Earth – the near side – is completely sunlit and appears as a circular disk, while the far side is dark. The full moon occurs once roughly every month.

When the Moon moves into Earth's shadow, a lunar eclipse occurs, during which all or part of the Moon's face may appear reddish due to the Rayleigh scattering of blue wavelengths and the refraction of sunlight through Earth's atmosphere. Lunar eclipses happen only during full moon and around points on its orbit where the satellite may pass through the planet's shadow. A lunar eclipses does not occur every month because the Moon's orbit is inclined 5.14° to the ecliptic plane; thus, the Moon usually passes north or south of Earth's shadow, which is mostly restricted to this plane of reference. Lunar eclipses happen only when the full moon occurs around either node of its orbit (ascending or descending). Therefore, a lunar eclipse occurs approximately every 6 months and often 2 weeks before or after a solar eclipse, which occurs during new moon around the opposite node.

The interval period between a new or full moon and the next same phase, a synodic month, averages about 29.53 days. Therefore, in those lunar calendars in which each month begins on the day of the new moon, the full moon falls on either the 14th or 15th day of the lunar month. Because a calendar month consists of a whole number of days, a lunar month may be either 29 or 30 days long.

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Moon Phase Terms
Full Moon & New Moon Calendar for 2018

Full Moon - The moon is full when the moon is on the opposite side of the Earth from the Sun. Another way to look at it is that the moon, sun and earth are in a line with the earth being between the sun and moon. When this occurs the entire surface of the moon looks to be illuminated. The full moon occurs every 29.53058 days.

New Moon - A new moon occurs when the moon is between the earth and the sun. We are seeing the oposite side of the moon that the sun is shinning on. At the exact time of the New moon the moon is to close to the sun to see at all.

Blue Moon - Today we consider the Blue Moon to be when a full moon occurs twice in one month. This is a relatively new concept for the term. Originaly a blue moon was considered to be when a full moon occured 4 times in a season. A season usualy has 3 full moons. The term has became popular when referring to any rare event.

Super Moon - A new or full moon which occurs with the Moon at or near (within 90% of) its closest approach to Earth in a given orbit (perigee). In short, Earth, Moon and Sun are all in a line, with Moon in its nearest approach to Earth.

Black Moon - This is a term that is not used frequently and has no exact definition. Some sources use this term when there are 2 new moons in one month similar to the blue moon which is 2 full moons in a month. It is also the term used when there is no full moon in a month. Having a month with no full moon is very rare. It can only happen in the month of February since is has fewer days then the full moon cycle of 29.53058 days.

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The modern day definition of a Blue Moon is when there are 2 Full Moons in one Month. A Full Moon occurs roughly every 29.5 days and on the rare occasions when the Full Moon falls at the very beginning of a month there is a good chance a Blue Moon will occur at the end of the month. According to this definition the next Blue Moon will occur on January 31, 2018.

Depending on the exact time of the Blue Moon it is possible that some places in the world don't technicly have a Blue Moon. As an example the Blue Moon on August 31, 2012 occured exactly at 13:58 UT. The Blue Moon will occur on August 31 for South America, North America, Europe, Africa, Asia, India, and Austrialia but New Zealand will just miss out. For New Zealand the Full Moon occurs just past mid-night on September 1st. For exact times of the Full and Blue Moons see the Full Moon Calendar.

The modern definition of a Blue Moon was derived from an earlier idea of what a Blue Moon was. This earlier definition says a Blue Moon is when there are 4 Full Moons in a season rather than the usual 3. The Blue moon is the 3rd Full Moon out of the 4. This definition gets a bit complicated and it's origins are murky. One school of thought has to do with the naming of the Full Moons. Many cultures named the Full Moons each month to reflected the times for planting, harvesting or seasonal conditions. When an extra Full Moon was thrown in it was referred to as a Blue Moon to keep the Full Moon names constant throughout the year.

Another origin could be from the Christian ecclesiastical calendar. This one gets even more tricky but basically has to do with the idea that there are usually 12 Full Moons in a year. The Full Moons on this calendar were important markers for determining curtain dates such as Easter. When a 13th Full moon was thrown into the year it made things messy so giving it a name allowed the calendar to stay on track.

The idea of a Blue Moon being the extra full moon in a season (or when there were 13 in a year) was widely used in 19th and early 20th center Farmers Almanacs and the more modern version seems to have come from an article written in the 1930's that misinterpreted the Farmers Almanac definition. The article was names "Once in a Blue Moon" and from that point on the term became part of popular culture.

This is a very rare event but it does happen. There are a few recorded events when forest fires or ash volcanic eruptions have given the moon a bluish color. The moon can also has a blueish color on very cold winter nights when ice crystals in the air form a ring around the moon. Of course the idea of the moon being blue is very subjective and left up to ones own interpretation.

An interesting twist to the idea of a Blue Moon is the idea of Dark Moon. Sometimes the reference of a Dark Moon is given when there are 2 new moons is a calendar month, the opposite of a Blue Moon. Other definitions say it is when there is no Full moon is a calendar month. Neither of these definitions or the term Dark Moon is used very often. Neither has any scientific bases and is more a part of popular culture.

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Blue Moon

A "Blue Moon" is a fairly infrequent phenomenon involving the appearance of an additional full moon within a given period. But which period — there are two definitions of the term, and one was borne out of a misunderstanding of the other.

The older meaning defines a Blue Moon as the third full moon in a season that has four full moons. Called a seasonal Blue Moon, this occurs about every 2.5 years, according to NASA. Why the third moon? There are roughly 29.5 days between full moons, making it unusual for two full moons to fit into a 30- or 31-day-long month. (This means that February will never have a blue moon.) Seasons normally have three full moons, and some of them, for traditional and religious reasons, must occur at specific times of the year. So, the "Moon Before Yule" is always the one before Christmas.

The other meaning is that a Blue Moon is the second full moon within a single calendar month. This definition — a "monthly Blue Moon" — has gained popularity in recent years because of a misinterpretation of an almanac's original definition.

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Black Moon

A Black Moon has multiple meanings. One commonly used definition is the second new moon in a month. The moon goes through several phases that skywatchers can see from Earth. During a full moon, the entire disc is visible. During a new moon, none of the disc is visible because the far side of the moon is lit by the sun, leaving the Earth-facing side in shadow.

According to skywatching columnist Joe Rao, Black Moons (under this definition) occur about every 32 months. The next Black Moon in North America will be Friday, Sept. 30. Berman added that there are other definitions of a Black Moon. One refers to a situation in which there are no new moons in an entire month. This is only possible during the month of February, which normally has 28 days. Because a lunar cycle is 29.5 days, it's possible for February to miss either a full moon or a new moon.

An even lesser-known definition for the Black Moon is the third new moon in a season of four moons. Berman said he is not sure where this definition originated.

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Chinese Lunar Calendar
Full Moon on 1st Jan 2018 in Gregorian calendar & on 15th Nov 2017 in Chinese calendar

Full Moon on 31st Jan 2018 in Gregorian calendar & on 15th Dec 2017 in Chinese calendar

Full Moon on 2nd Mar 2018 in Gregorian calendar & on 15th Jan 2018 in Chinese calendar

Full Moon on 31st Mar 2018 in Gregorian calendar & on 15th Feb 2018 in Chinese calendar

Full Moon on 30th Apr 2018 in Gregorian calendar & on 15th Mar 2018 in Chinese calendar

Full Moon on 29 May 2018 in Gregorian calendar & on 15th Apr 2018 in Chinese calendar

Full Moon on 28th Jun 2018 in Gregorian calendar & on 15th May 2018 in Chinese calendar

Full Moon on 27 Jul 2018 in Gregorian calendar & on 15th Jun 2018 in Chinese calendar

Full Moon on 25th Aug 2018 in Gregorian calendar & on 15th Jul 2018 in Chinese calendar

Full Moon on 24th Sep 2018 in Gregorian calendar & on 15th Aug 2018 in Chinese calendar

Full Moon on 23rd Oct 2018 in Gregorian calendar & on 15th Sep 2018 in Chinese calendar

Full Moon on 22nd Nov 2018 in Gregorian calendar & on 15th Oct 2018 in Chinese calendar

Full Moon on 21st Dec 2018 in Gregorian calendar & on 15th Nov 2018 in Chinese calendar

Chinese calendar, a lunisolar calendar, is formed on the movement of the moon.

Full Moon occurs on every 15th Day of the Chinese Lunar Calendar.

There are 2 Full Moons in January & March but no Full Moon in February 2018.

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Solar and Lunar Eclipses Worldwide – Next 10 Years
Featured Eclipses in Coming Years

Find Solar Eclipses, Lunar Eclipses, and Planetary Transits Worldwide from 1900 to 2199

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Full Moon August 2019
‘Blood moon’: Longest total lunar eclipse of the century
Ultra Rare 3-In-1 Moon Phenomenon
The Second Blue Moon of 2018
No Full Moon in February 2018
The first Blue Moon of 2018
Blood Moon 2014