HALLOWEEN FULL MOONS
 ------------------
 John Pazmino
 NYSkies Astronomy Inc
 www.nyskies.org
nyskies@nyskies.org
 2020 October 29

Introduction
 ----------
    The Frank Morano radio talk show on october 28 discussed with Dr 
Sy the Full Moon of Halloween. The show airs on WABC in New York, 
AM 770.  
    Among other topics, Dr Sky explained that in 2020 the Full Moon of 
Halloween actually occurs on October 31st. It is also a minimoon for 
being near its apogee and is a blue Moon for being the second Full 
Moon in October. 
    He further mentioned that the last time the Halloween Full Moon 
(HFM) came on October 31 was in 1944 and the next is in 2039.. He 
then moved along to other topics in astronomy and space. 
    I did check the minimoon and blue Moon easily enough but it 
puzzled me why there was such a long interval since the previous true 
Halloween Full Moon. 
    Perhaps Dr Sky did a tongue-slip or I misheard him? 

Full Moon
 -------
    Dr Sky stressed that a Full Moon stands 180 degrees from the Sun. 
178, 182 doesn't qualify. I assume he meant 180 degrees of ecliptic 
longitude, six zodiac signs, from the Sun. Actually the Moon can be up 
less than 180 degrees, to 175 degrees, from the Sun and still be full. 
    From the lunar orbit tilt against the ecliptic. the Moon usually 
passes north or south of the 180-degree point on the ecliptic.. 
    This point is the center of Earth's shadow. The Moon misses the 
shadow, preventing us from enjoying lunar eclipses at every Full In 
such situations the Moon is then a bit less, by up to dive degrees, 
than 180 degrees from the Sun. 

Lunar month
 --------- 
    Many early cultures assigned extra importance to the new and full 
phases. While the New Moon can not be directly seen for occurring next 
to the Sun in daytime, full Moon is visible at night when it should be 
easily inspected. 
    It isn't.
    To bare eye, as all astronomy was performed before the telescope 
era, it is revoltingly tough to tell when the Moon is in fact 'full'. 
It looks awfully round a day away from geometric full phase. Even 
sharp eyes may have trouble seeing a defect of shape on a Moon two 
days from full. 
    This is why Halloween full Moons are allowed up to two days off of 
October 31, The very large, imperfectly full, Moon serves quite well 
as a  halloween Full Moon. 
    One common strategy of early peoples using the Moon for calendar 
keeping is to recognize that the Full Moon is always half way between 
the previous and next New Moon. With the New Moons spaced 29-1/2 days 
apart, the synodic period, the Full Moon is on the 14th or 15th day 
after each New Moon. 
    With no feasible way to actually spot the New Moon (except during 
a solar eclipse)  the early skywatchers strived to spot the very first 
appearance of the thin sliver of lunar crescent a day after true new 
phase. This event is Firest Crescent. 
    First Crescent is already one day into the new cycle of phases,  
putting the full Moon 14 days later.. In a pure lunar calendar the 
month begins at first Crescent, Full Moon is on the 15th day of the 
month, the month ends at the next First Crescent. New Moon falls on 
the last day or two of the month. 

My conjecture 
 ------------------ 
    I'm making a conjecture now. 
    Starviewngs in the NYSkies region commonly begin near sunset.  
Visitors have daylight to find the viewing site, examine the scopes, 
pick up litterature, socialize, study starcharts. 
      We usually schedule starviewing on dates with a waxing crescent 
Moon. The Moon is our first target until nightfall.  The Moon also is 
insurance against thin or broken  clouds. . 
    On these occasions we sometimes demonstrate the lunar phases with 
a small rough surface ball. A Spalding, tennis ball, styrofoam crafts 
ball are common props.. 
    Holding the ball ,in sunlight, against the Moon, its phase is the 
SAME PHASE as the Moon's! By sliding the ball to and from the Sun we 
show the phase changes over the lunar phase cycle.. 
    My question:, Could an ancient skywatcher try this trick to 
determine Full Moon without counting days from the previous New Moon? 
it would be far easier to tell if the ball isn't quite fully lighted 
when the very Moon does look good and round. The Moon really is not 
yet full. A do-over is tried on the next day. 
    I have no positive knowledge of any ancient people using the ball 
technique. If it did, it could possibly be buried in its vault of dark 
arts. 

Rule-of-19 
 --------
    Breve mente, the motions of the Moon follow the rule-of-19. For a 
a phase and place in the zodiac for a given calendar date, the phase 
and place repeat at 19 calendar year intervals. The rule is not 
precise, unwinding after several laps, but it is good for a couple 
generations or even a full century. 
    At first I figured there was a break in the rule prior to 2020, 
with the 1944 year belonging to an other 19-year series.
    I cranked up various astronomy software and found that, lo!, the 
instant 19-year series endures from at least the early 19th century 
into the the 22nd. And year 1944 is in fact one of the instances in 
this series. 
    What happened in the next years 1963, 1982, 2001? By a calendar 
slip the halloween Full Moons came on November 1st, one day off of 
October 31st.
    Dr Sy was correct. The true HFM before 2020 was in 1944. 

Blue Moon
 -------
    Dr Sky, and most astronomers, count blue Moons by the simpler 
definition, the second Full Moon in a calendar month. The strict blue 
Moon is based on the number of Full Moons in each calendar quarter and 
is largely passed over for public notice. 
    A Full Moon on the 31st must have one on or near the 2nd of 
October. This makes every October 31 HFM a blue Moon. 
   For Full Moons on November 1, which occur several times before 2020 
and continuously star in the 22nd century, there is a second Full Moon 
on November 30. There is a blue Moon associated with, but actually 
being, the HFM. The one exception is in year 2115, when the HFM is on 
November 2. The next Full Moon is on December 1, missing a blue Moon 
associated with the HFM for that year. 
    Blue Moons by the simple meaning occur a couple times each year. 
A calendar month is one or two days longer than the lunar synodic 
cycle, 30 or 31 days versus the Moon's 29-1/2 days. In every month 
(except in short February) there is a rollover of one synodic cycle 
into the next one. A couple days phase at the start of a month repeat 
at the end of the month. even if not for a the cardinal phase. 

Minimoon
 ------
    A minomoon is a Full Moon coinciding with the Moon's apogee. A 
supermoon is coincience with the perigee. It being amost impossible to 
get perfect coincidence, I allowed a one day leeway. The HFM in 2020 
is one ay aftr rounding apogee and is fair and square a minimoon. 
    There is no strong pattern of mnimoon, or supermoons, for the 
current 19-year series. Minimoons and supermoons tend to alternate on 
the third or fourth HRM in the series, but not consistently. 
    The angular size difference between a perigee ad apogee Moon is 
some 13 %, too small to notice by bare eye. Some of us take pictures 
of both with the same camera configuration and compare the two 
pictures. The perigee, supermoon, image is definitely much bigger than 
the apogee, minomoon, image. 

Geographic effects 
 ----------------
    All of my work here is for New York City, longitude W 73.9 degree. 
Due to the long span of years, during which the observance of Daylight 
Savings Time varied erraticly, I stayed with Eastern Standard Time. 
    In timezones east of the City the Moon is earlier than full rising 
a little earlier  relative to sunset. Western timezones have a later 
moonrise because he Moon moved a bit later than full phase. In severe 
separation of timezones from New York, the HFM could slip into the 
next or previous day, causing distortions in the rule-of-19. 
    Latitude affects the sunset-moonrise aspect. On October 31 the Sun 
is near Scorpius 10 or ecliptic longitude 220 degree. The Moon is 
opposite the Sun, near Taurus 10, 40 degree. 
    Sunset is near southwest while  moonrise is near northeast. The 
tilt of the horizon, according as the observer's latitude, can cause 
large shifts in the hour of sunset and moonrise. 
    Latitudes north of the City may see an earlier sunset with later 
moonrise. Vice versa for southward latitudes. 

Appulses
 ------
    The Halloween Full Moon is in Aries-Taurus. shortly after moonrise 
the Pleiades star cluster is 15--30 degrees left to lower-left of the 
Moon. The wide range of distance results from the exact hour of Full 
Moon, which may be up to 18 hours before to 6 hours after moonrise.  
In 2115 the HFM is on November 2 and sees the Pleiades about 10 
degrees to the the left. An hour or so after moonrise the Hydes 
cluster and Aldebaran rises below the HFM. This scene prevails thruout 
the 400 year range of HFMs in this article 
    I looked at HFMs for 1944, 1963, 1982, 2001, 2020, 2039 for any 
bright planets near the Moon. In 2020 Mars is some 5 degrees above the 
Moon. Mars rounded its opposition on 2020 October 13 and is by far the 
brightest 'star' in the east in evening twilight. In 2001 Saturn is in 
mid Taurus, a little east of the Hyades.it rises about an hour after 
the Moon.              

Eclipses
 ------
    Dr Sky alerted audience to the lunar eclipse of May 2021, outside 
of any relation to the HFM. Are there any lunar eclipses at an HFM? 
    In the whole span of the 19-22 centuries there are only three 
eclipses, all in consecutive 19-year instances in the 2100s. altho the 
HFM is on November 1 or 2, not October 31. 
    All three eclipses are visible from New York City and all ere are 
at the lunar ascending node. None occur at moonrise, so there are no 
strict selenehelia. 
    All other HFMs in te 400ish year range are too far from the 
nearest node to make an eclipse. 

Selenehelia 
 ---------
    The strict selenehelion is a lunar eclipse in progress at sunrise 
or sunset. We in the City enjoyed the previous one at sunrise in 
January 2019. Some of us took pictures showing the umbra coming over 
the Moon with trees and buildings lighted by the Sun. 
    The simpler selenehelion is a Full Moon rising at sunset or, less 
commonly, a Full Moon setting at sunrise. The latter is largely
neglected because the Full Moon is in the sky all night until sunrise. 
The Full Moon at sunset makes its first appearance for the night. The 
most memorable selenehelion for the City was in July 2014 during a 
Manhattanhenge. 
    Having the Moon geometricly full at sunset is rare, like in a 
lunar eclipse in a strict selenehelion. Here I looked for the HFM 
rising a few minutes before sunset, even tho the geometric Full Moon 
is several hours away from moonrise This lets the Moon comes into view 
while the Sun is still in sight. 
    In the 19-21 centuries the HFM rises after sunset, failing to make 
a selenehelion. In the 22nd century most HFMs rise a few minutes 
before sunset, offering several selenehelia. 
    The selenehelion in  2153 is touch-&-go. The Moon rises a couple 
minutes after sunset. It's possible that atmosphere refraction can 
delay geometric sunset and advance geometric moonrise so the Moon is 
in sight with the Sun. 

Halloween Full Moons 
 ------------------
    This table gives all Halloween Full Moons in the 19th ro 22nd 
centuries, with hours in Nw York time. For many I state other features 
of the HFM, such as supermoon and partial eclipse. The hour may differ 
fro other sources due to the various methods of working with the lunar 
orbital motions. 

 -----------------
 1811 Oct 31 12:03 
 1830 Oct 31 12:03 supermoon 
 1849 Oct 31 11:47
 1868 Oct 31 06:06
 1887 Oct 31 16:32

 1906 Oct 31 23:46
 1925 Oct 31 12:16
 1944 Oct 31 08:36
 1963 Nov 01 08:57 supermoon 
 1982 Nov 01 07:59

 2001 Nov 01 00:43
 2020 Oct 31 09:51 minomoon 
 2039 Oct 31 17:37
 2058 Oct 31 07:55
 2077 Oct 31 05:39 supermoon 
 2096 Oct 31 06:20 supermoon 

 2115 Nov 02 04:32 partial eclipse
 2134 Nov.01 19:37 total eclipse, selenehelion 
 2153 Nov 01 03:45 partial eclipse, selenehelion?, supermoon 
 2172 Oct 31 12;25 selenehelion
 2191 Nov 01 04:31 selenehelion
 ------------------------------

Conclusion
 --------
    A casual comments about the Full Moon of Halloween, heard on a 
radio talk show, can lead to an excursion into the workings of the 
Moon! 
    In the City Halloween was chilly and raw. I was cozy up in my 
house with the heat running.
    The [not quite so big] Full Moon shined thru my window, between 
broken clouds. This year she played on me a few tricks and treats.