Sky and Telescope - February 2018 - 84

FOCAL POINT by Dave Chapman

February's Missing Moon
THE FIRST THREE MONTHS of 2018

have an unusual sequence of full Moon
dates. As seen from the Americas,
those dates are January 1st, January
31st, March 1st, and March 31st. This
sequence leaves February with none. As
many S&T readers know, these events
have no scientiﬁc or spiritual signiﬁcance. They're simply an idiosyncrasy of
our imperfect civil calendar.

As with other
cultures following
the Moon, these
original Americans
inserted a 13th Moon in
the sequence every two
to three years, to keep
the lunar times in step
with the seasons.
The average time between two full
Moons is about 29½ days. But 11 of the
12 months are longer, 30 or 31 days.
Therefore, it's possible from time to
time for one of these months to contain
two full Moons. Typically, a month
with two full Moons occurs once every
two to three years.
The outlier, of course, is February
with its 28 days (29 in a leap year).
February can have no full Moons, as
in 2018, but never two. Moreover, if
you do the math, you'll ﬁnd that when
February has no full Moons, then both
January and March that year must
contain two full Moons. This pattern is
infrequent: It occurred most recently in
1999 and will happen again in 2037.
84

FE B RUA RY 2 018 * SK Y & TELESCOPE

Some traditional calendars, such as
the Hebrew and Chinese calendars, have
months that exactly follow the lunar
cycle. Various indigenous peoples of
the Americas, including the Mi'kmaq
nation of Canada's Atlantic Provinces
where I live, also reckoned the passage of time this way. Each moon cycle
was linked to the season by ecological
descriptors such as "Rivers About To
Freeze" or "Frog Croaking Time." As
with other cultures following the Moon,
these original Americans inserted a
13th Moon in the sequence every two to
three years, to keep the lunar times in
step with the seasons. Since these calendars are Moon-based, they never had a
moonless month.

The ancient Roman calendar was
similar. But priests continually made
a mess of it until Julius Caesar, in the
1st century BC, instituted a calendar reform that divorced the months
from the lunar cycle by adding days to
months here and there - and, curiously, by shortening the month we
know as February. The motivation was
to synchronize the calendar with the
Sun and the seasons, an idea imported
from Egypt. Such a calendar was more
in tune with annual events of agricultural importance, such as the ﬂooding
of the Nile.
In the 16th century, Pope Gregory
XIII tweaked the Julian calendar, but
the month lengths remained the same.
It is these longer Julian and Gregorian
months, now disconnected from the
actual lunar cycle, that can contain two
full Moons.
Eventually, the Gregorian calendar
took precedence in the Americas for
spiritual, legal, and political purposes,
but even today many indigenous
nations still observe the traditional
lunar times. Once in a while, there are
two full Moon names corresponding
to a given month, and, more rarely, a
February with no full Moon. This is a
time of extreme disparity between the
indigenous and European calendars, but
it passes in subsequent years.
Meantime, such a disconnect offers
an opportunity to reﬂect on how various peoples understand the passage of
time - and, perhaps, on the Moon's
role in helping us grapple with it.
¢ DAVE CHAPMAN is emeritus editor
of the Observer's Handbook of the Royal
Astronomical Society of Canada, of
which he is a Life Member. He lives in
Dartmouth, Nova Scotia.

A A RON RU T TEN / BIGSTOCK PHOTOS.CO M; M OON: N ASA

Don't be alarmed. It's just a quirk of the Gregorian calendar.
http://www.BIGSTOCKPHOTOS.COM
Sky and Telescope - February 2018

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