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WINTER SOLSTICE LUNAR ECLIPSE --------------------------- John Pazmino NYSkies Astronomy Inc nyskies@nyskies.org www.nyskies.org 2010 December 3 Introduction
----------
The total lunar eclipse of 20-21 December 2010 is visible in its
entirety thruout North and South America. Western Europe sees only the
beginning phases until local moonset. Western Pacific lands see only
the ending phases after local moonrise.
Please note well that the eclipse for New York (and similar
longitudes) occurs in the owl hours of December 21st, after the
midnight that closes December 20th. If you look for the eclipse on the
evening or night of the 21st, you missed it by 12 or more hours.
The last total lunar eclipse in New York was on 21 February 2008
from evening to midnight. The next one is on 15 April 2014 in owl
hours. Lunar eclipse are common enough to recall the last one you saw,
yet rare enough to aniticipate the next one.
A lunar eclipse is completely safe to watch with any optics. Many
astronomers prefer the naked-eye or low-power binoculars, but you may
use regular telescopes with perfect safety. A solar eclipse, on the
other hand, poses serious risk of eye damage if viewed without proper
filtration or projection.
Timetable
-------
The timetable here gives the events for New York City. They are
valid for locations thruout the NYSkies region. Of special value are
the altitude and azimuth of the Moon. These help you plan for a
suitable viewing location. On the whole you need a clear view to the
southwest and west. A high skyline will cut short your view, perhaps
before totality ends.
---------------------------------------------------
LUNAR ECLIPSE 20-21 DECEMBER 2010 FOR NEW YORK CITY
---------------------------------------------------
EST | event | alt-az | comments
------+-------------------+--------+---------
15:58 | moonrise | 00 058 | Moon before full
16:32 | sunset | 05 063 | December 20th
17:36 | nautical twilight | 15 072 | full night in NYC
23:45 | moon transit | 73 180 | due south, highest alt
00:00 | midnight | 72 190 | Dec 20 -> Dec 21
00:29 | 0th contact | 71 211 | enters paenumbra
01:19 | first shading | 64 245 | enters deep paenumbra
01:32 | star ingress | 62 240 | pos 119d, ver 74d
01:34 | 1st contact | 62 240 | enters umbra
02:41 | 2nd contact | 50 258 | totality begins
02:44 | star egress | 50 258 | pos 255d, ver 211d
03:16 | Full Moon | 44 264 | geometric moment
03:17 | midtotality | 44 264 | deepest in umbra
03:53 | 3rd contact | 37 270 | totality ends
05:01 | 4th contact | 25 280 | leaves umbra
05:16 | last shading | 22 382 | leaves deep paenumbra
06:04 | 5th contact | 14 289 | leaves peaenumbra
06:19 | nautical twilight | 11 291 | end of full night
06:40 | winter solstice | 08 294 | Sun enters sign Capricorn
07:17 | sunrise | 01 300 | December 21st
07:31 | moonset | 00 302 | Moon after full
------+-------------------+--------+----------------
Times here may differ by a minute from other sources ue to
algoritms and rounding.
Shadow geometry
-------------
The shadow of Earth is like that of any shadow thrown by the Sun.
It has a dense inner zone, the umbra (UMM-bra) and a thinner diffuse
outer zone, the paenumbra (penn-UMM-bra). The umbra is circular,
matching the globe of the world. Within the umbra the Moon is blocked
from all sunlight by the opaque Earth.
The paenumbra is a broad border around the umbra that shades
gradually darker from its outer edge toward the umbra. The outer aone
imparts no darkening on the Moon for being too thin. About 15 minutes
before the Moon reaches the umbra, the paenumbra appears as a smoky or
misty shading on the side where the umbra will later touch.
In this eclipse totality, the interval when the Moon is fully
immersed in the umbra, is 1h 12m. This is among the longer eclipses
in recent decades.
Unlike a solar eclipse, where you have to stand within the path of
the Moon's shadow as it sweeps over the Earth, a lunar eclipse is
visible from anywhere the Moon is in sight. This is a little more than
1/2 of the globe, with the bit extra given by the diurnal rotation of
Earth during the eclipse. A solar eclipse path covers only 2% of the
Earth surface and is only 100-200 kilometers wide.
Umbral darkness
-------------
The density or darkness of the umbra varies widely among eclipses.
It is not always the textbook cherry or copper red hue. In a light
eclipse the larger craters and maria are distinctly visible in
binoculars. A dark eclipse can blot out the Moon almost completely.
She is then hard to find by eye or binoculars in the sky.
There are no large volcanos or dust storms around the world in
fall of 2010. Such in the past filled the atmosphere with obscuring
dust and soot, blocking sunlight from reaching the umbra. This
sunlight is bent into the umbra by the atmosphere giving it a reddish
luminance on the lunar disc. With no sunlight, the Moon is rendered
black or daek gray against the sky.
Expectations are for a more or less normal darkness with maria
visible and a deep red tint. Be prepared for surprises.
Ecliptic
------
The path of the Sun thru the stars is essentially fixed year after
year, so it can be drawn permanently on star charts. This line is the
ecliptic and is the centerline of the zodiac. It runs thru the
tradtional 12 signs, Aries thru Pisces.
The center of the Earth shadow paces the Sun in the ecliptic but
is exacta mente opposite in the sky. This point is also called the
antisolar or midnight point.
For the Moon to run thru the umbra she must also be on or very
close to the ecliptic. Usually she is too far north or south of that
line and misses the shadow. You get a regular full Moon.
The Moon is near the ecliptic when she crosses from north to south
or vice versa. The crossing point is a node, and for this eclipse it
is a north-to-south, or descending, node. If the Moon was running
south-to-noth, she is at her ascending node.
It is the coincidence in time of the full Moon and a node crossing
that makes a lunar eclipse. One condition without the other misses an
eclipse, even tho there are ascending node, descending node, and full
Moon twelve or so times each year.
Occultation
---------
Just about at first and second contacts we are treated to an
occultation! The Moon slides over a 7th magnitude stars at 01:32 and
slides off of it at 02:44. Such an occultation would be difficult, if
not impossible, to observe at a normal full Moon because of the glare
from the lunar disc.
This star is too faint to have a Bayer or Flamsteed number. It is
in Taurus, magnitude +7.0, spectrum K5, RA 05h 52.5m, DE +23d 23m. You
may look up the star by several other catalog designation:
BD+23:1087 HD39184 PPM94989 SAO77647 TYC1863-1341-1
XZ7747 ZC887
During this eclipse the ingress on the Moon's limb is just about
at the first contact point, where the umbra will a minute later hit
the disc. it is heavily shaded by deep peaenumbra. The egress is just
about at the second contact point, where the umbra completely covers
the disc.
Seeing this star on both sides of the Moon about an hour apart
helps demonstrate that it is the Moon who moves thru the stationary
Earth shadow as she continues eastward along her orbit thru the stars.
Never the less, we often speak of the 'shadow moving over the Moon'.
The timetable gives two angles for the ingress and egress of this
star. 'pos' is the position angle in degrees CCW around the lunar disc
from celestial north. 90 degree is east (astronomical); 180, south;
270, west. This angle is applied for an equatorially mounted telescope
or a star atlas.
'ver' is the vertex angle CCW around the lunar disc from the top.
90 degree is left; 180, bottom; 270, right. This angle is aookied for
an altazimuth telescope or a skyscape chart with zenith at the top..
Comet Hartley-2
-------------
By 2010 December 20 comet 103P/Hartley-2 lasped back into
telescope range, fading rapidly as it recedes from Sun and Earth.
During totality observers may try to spot the comet for possibly their
last time from the City area.
The data below are for 0h UT on the 20th and 21st surrounding the
eclipse. An extra point is interpolated for midtotality on the 21st.
=========================================
Orbital elements are taken from MPC 70362
-----------------------------------------
Epoch 2010 Oct. 11.0 TT = JDT 2455480.5
Peri T 2010 Oct 28.2670 TT
Peri AU 1.058693 (2000.0)
M D M 0.1523112 Arg Peri 181.2025
S M A 3.472547 Asc Node 219.7600
Excenty 0.695125 Inclintn 13.6184
Period 6.47y
-----------------------------------------------
Date 0hUT R A (2000) Decl Earth Sun Elong Mag
---------- -------------------- ------ ------ ----- ---
2010 12 20 07 28 26.3 -18 13 38 0.3902 1.2782 132.0 8.6
2010 12 21 07 27 36.2 -18 11 38 0.3961 1.2855 132.6 8.7
2010 midtot 07 27 19.3 -18 10 40 0.3981 1.2880 132.8 8.7
2010 12 22 07 26 45.5 -18 08 46 0.4020 1.2929 133.3 8.8
-------------------------------------------------------------
Rule-of-19
--------
The curious fact that this eclipse occurs on the winter solstice
inspired inquiries about other instances of a winter solstice lunar
eclipse. These in turn headed toward the review of the Rule-of-19.
The Rule-of-19 states that given one date for an eclipse, there
are other eclipse on the same date spaced 19 yearss apart. The rule
works for occultations of a given star and for solar eclipse, too.
The rule lasts for four or five rounds before it unravels. Also,
there can be a hiccup in the calendar that slides the date one day off
of the initial one. In the case of the solstice, it can fall on
December 20th in some years, again due to calender hiccup.
When one eeries peters out, a new series begins a few years later
to continue the trend. Because the motions of Sun and Moon are not
nitid ratios, the date in the Rule-of-19 gently drifts from series to
series. It just happens in the current series to fall on/near the
winter solstice.
Here are lunar eclipse on/about December 21st for a century or so
around year 2010. The dates are for UT, not New York.
series 1: 1842 1861 1880 1899 1918
December: 17 16 16 17 17
series 2: 1926 1945 1964 1983
Decemebr: 19 19 19 20
series 3: 1991 2010 2029 2049
December: 21 21 20 20
series 4: 2056 2075 2094 2113 2132
December: 22 22 21 22 22
series 5: 2140 2159 2178 2197
December: 23 24 24 24
Winter sky
--------
This eclipse occurs on the day of the winter solstice. This is not
particularly significant in as much as the last instnce for the City
was in 1991. There is a wait until the next occasion in 2094. However,
for those celebrating the solstice, rather thna the usual yearend
holidays, this eclipse can be a bonus treat.
With the Sun at the winter solstice point, at the cusp of sign
Capricornus, in constellation Sagittarius, the eclipsed Moon is at the
summer solstice point, opposite from the Sun. This is at the cusp of
sign Cancer, constellation Gemini. She is in the middle of the Winter
Hexagon or Superbowl Footbla asterism.
It would be a fritter of good time to explore the permanent points
of interest in this area during the eclipse because this region comes
into the ight and evening sky in January and February. You can and
should acquaint yourself with the brighter stars here.
On the other hand, there could be a variable star, new comet
(besides Hartley-2), nova that can not be observed under full or large
Moon conditions.
It is also the good time to scan for aurorae. With solar activity
on the rise, it can't hurt to give the sky a good inspection while it
is darkened by the eclipsed Moon.
Winter conditions
---------------
It is the beginning of winter season but winter weather is already
in force over much of NYSkies land. You must dress for the cold and
wind, or else suffer extreme discomfort and potential health hazards.
You don't have to stand outdoors continuously for the eclipse,.
Retreat into shelter to warm up and take looks every few minutes. The
clipse progresses slowly with no sudden activity to miss with an eye
blink.
The one exception is the occultation. You must keep vigil at the
telescope for many minutes to follow the star toward or away from the
lunar limb. Even for this event you may shelter yourself between the
ingress and egress.
The eclise can be viewed from inside a darkened room thru an open
window. The window may be closed between looks to lessen the chill.
If you're looking only be eye you may leave the window closed. Be sure
to clean it well on both sides as part of your eclipse preparation.
Sky conditions
------------
As precisely as we can foretell an eclipse decades and centuries i
the future, we are abysmally unable to forecast the local weather even
a few days in advnce. A lunar eclipse is a long-running event, about
3-1/2 hours for this one.
A spell of passing clouds should not interfere too severely with
your overall enjoyment. As a matter of experience, a few clouds
scattered around the sky, the sort that moonlight can play on, can
enhance the effect of the eclipse on thee night scene.
Even thin overcast or haze will allow good views. Of course, thick
overcast, with rain or snow, will terminate your eforts to watch the
eclipse.
The Moon in the aerly stages of the eclipse is at high altitude.
You may want to sit in a lawn chair or other reclining seat. By
totality the Moon declined to a more comfortable altitude to watch
while standing or sitting upright.
Diagrams
------
The first of the three diagrams below is from Goddard Space
Flight Center showing the stages of the eclipse. North is up and the
Moon moves from west (right) to east (left) thru the Earth's shadow.
The 0th and 5th contacts with the outer rim of the paenumbra are
omitted because there is no visible effect on the Moon at these
moments. The chart must be rotated to line up with the Moon in the
sky. Approximately it is turned clockwise by 45 degrees.
The next diagram is a skyscape of the eclipse with the Moon among
the stars of the winter sky. The horizon is under the chart with
zenith near the top center. The brighter stars are labeled. These
stars are in the evening sky before and after the eclipse but in
the east and rotated by diurnal motion of the sky from then to the
owl hours.
The last diagram is an ecliptic panorama showing the planets and
other points along the zodiac. The zodiac signs (not constellations)
ring the sky from Scorpius rising in the east thru Leo in the south to
Taurus setting in the west. The Moon is in southwest during totality
and is in conjunction with Betelgeuse at chart time. The Sun and lunar
ascending node are opposite from the Moon. The Moon is near the
descending node, not marked, and far from the apogee. Saturn is
visible in the east while all others planets are down.
Last update on 13 December 2010 |
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