......................................................................................
Blue Moons
When Is the Next Blue
Moon?
There are two definitions of
a Blue Moon; both are a type of Full Moon and have nothing to do with
color.
If the Moon looks blue, it's
because of dust in the atmosphere.
How Rare Is a Blue Moon?
May 2019's Flower
Moon is a Blue Moon
The term once in a Blue Moon suggests
something happens very rarely. So, how often do Blue Moons occur?
The
answer depends on how you define a Blue Moon.
Two Definitions
There are two ways of calculating
the date of a Blue Moon.
1.
Seasonal Blue Moon = The third Full Moon in an astronomical
season with four Full Moons (versus the usual three).
2.
Monthly Blue Moon = The second Full
Moon in a month with two Full Moons.
In the 1100 years between 1550
and 2650, there are 408 seasonal Blue Moons and 456 monthly Blue Moons.
This
means that either Blue Moon occurs roughly every two or three years, although
the monthly ones are a little more frequent than the seasonal ones.
Blue Flower Moon in May
The seasonal Blue Moon is the
original astronomical definition of a Blue Moon.
Usually,
there are three Full Moons between each astronomical
season, which is the time between each solstice and
equinox.
But
some years, there are four Full Moons in a season. When this happens, the third
Full Moon is called a Blue Moon.
In 2019, May's Full Moon
is a seasonal Blue Moon. The astronomical season started with the
equinox on March 20, and the first Full Moon alignment was less than four hours
later; on March 21.
The
second Full Moon was on April 19, and the third, the Blue Moon, is on May 18.
The fourth and last Full Moon before the June solstice is
on June 17.
Not the Same Worldwide
All dates mentioned are based on UTC time.
There is some variation due to time zone differences.
Look
up local times for
Moon Phases along with information about lunations, Supermoons, Micromoons, and Black Moons.
You
will also find Full Moon names for the Northern
Hemisphere.
Two Full Moons in the Same Month
The calculation of the dates for
monthly Blue Moons is based on the 12 12 months in
our calendar rather
than astronomical seasons.
A lunar month – the time between two Full
Moons – is around 29.5 days long, while most calendar months are longer.
Because of this, most months have only one Full Moon. Some years, however,
there are two Full Moons in the same month, and the second one is often called
a Blue Moon.
In many Northern Hemisphere
cultures, each month's Full Moon is named after a specific
seasonal or natural phenomena, for example, Harvest Moon.
When
there are two Full Moons in a month, the second one doesn't have a proper name.
The
term Blue Moon has over time become a placeholder name for the extra Full Moon.
This way, the other 12 Full Moons keep their rightful place in relation to the
solstices and equinoxes.
Why Are There Different
Definitions?
The reason the second definition of Blue Moon exists is due to an
error originally made by amateur astronomer James Hugh Pruett (1886–1955).
He
misunderstood the basis for calculating the seasonal Blue Moon and wrote that a
Blue Moon was the second Full Moon in a month in an article published in Sky
& Telescope magazine in 1946.
This
erroneous definition since spread, particularly after it was quoted in a
popular radio program called StarDate in 1980 and then appeared as an answer in
a 1986 version of the board game Trivial Pursuit.
Today,
it is considered a second definition rather than a mistake.
Double Blue Moon
In 2018, there were two Full Moons
in January and March in most time zones. This is sometimes
called a double Blue Moon and takes place only about three to five times in a
century. This will happen next in 2037.
Other combinations of Blue Moons
also exist. Between 1550 and 2650 there are 20 years that have one seasonal and
one monthly Blue Moon.
The
next time is in 2048 while
the previous time was in 1934.
Triple
Blue Moons, a combination of one seasonal and two monthly Blue Moons in the
same calendar year, happens 21 times in the same time span. The next is in 2143,
while the last time was in 1961.
There can never be a double
seasonal Blue Moon, as that would require 14 Full Moons in the same year, which
is not possible because the time between two Full Moons is
approximately 29.5 days.
Some years, February has no Full
Moon at all, which is called a Black Moon.
The Rarest Blue Moon
A Moon that actually looks blue,
however, is a very rare sight. The Moon, full or any other phase, can appear blue when the
atmosphere is filled with dust or smoke particles of a certain size: slightly
wider than 900 nm.
The
particles scatter the red light, making the Moon appear blue. This is known as
Mie scattering and can happen for instance after a dust storm, a forest fire,
or a volcanic eruption.
Eruptions like the ones on Mt.
Krakatoa in Indonesia (1883), El Chichon in Mexico (1983), on Mt. St. Helens in
the US (1980), and Mount Pinatubo in the Philippines (1991) are all known to
have made the moon look blue.
Some
people even suggest the term once
in a Blue Moon is based on these rare occasions, rather than
the Full Moon definitions above.
Red Moon
The Full Moon can look red if other sizes of
dust particles fill the atmosphere or during Total Lunar Eclipses, which are much more
common than Moons that look blue.
Super Blue Blood Moon Eclipse
On the night of the Blue Moon on January 31, 2018 (UTC), there was a total lunar eclipse.
A totally eclipsed Moon usually looks red, and because of this coloring, it is
sometimes called a Blood Moon.
So,
this was a rare opportunity to see a red Blue Moon. If this wasn't enough, it
was also almost a Supermoon, earning it the nickname Super Blue
Blood Moon.
Blue Sky and Red Sunset
A similar phenomenon is Rayleigh
scattering, which occurs when light strikes a molecule of air. This
scattering causes the sky to look blue in the daytime and red at sunrise and
sunset.
|
When volcanoes
erupt, the dust particles can cause the Moon to appear blue.
|
No comments:
Post a Comment