HORIZON ECLIPSES
--------------
John Pazmino
NYSkies Astronomy Inc
www.nyskies.org
nyskies@nyskies.org
2020 July 17
Introduction
----------
New York City gets its share of lunar and solar eclipses. Home
astronomers and the public look foreard to them as marvels to watch.
It happened that so far in this 21st century many eclipses are near
the horizon, with part of the event occurring below it. These are the
'horizon eclipses' which can be specially spectacular.
I had the idea to compile this article in fall 2014 after
New York saw three horizon eclipses in the preceding twelve months.
The thought faded until I saw the two horizon eclipses coming up in
spring 2021. I collected some material to work on in winter 2020-2021.
It took a really magnificent event, a miss by a few minutes! for
the City, to push me to the keyboard. On June 19th, 2020, Venus was
occulted by the Moon. It was a dawn event. Venus emerged from the Moon
and a couple minutes later the Moon rose with Venus just off of her
upper right limb. That's it. Here's the horizon eclipse article.
I review here the horizon eclipses from 2000 thru 2030. For this
piece the Sun or Moon has some eclipse covering when they are at the
horizon. Eclipses tHat run their full course above the horizon are not
considered here.
Eclipse phases
-----------
As a quick review, an eclipse procedes in phases, steps, stages,
called 'contacts' The tables here outline hem for the various kinds of
eclipse
-------------------
TOTAL SOLAR ECLIPSE
-------------------
1st - Moon starts entering Sun - partial phase begins
2nd - Moon fully enters Sun - totality begins
3rd - Moon starts leaving sun - totality ends
4th - Moon fully leaves Sun - partial phase ends
==========================================
ANNULAR SOLAR ECLIPSE
---------------------
1st - Moon starts entering Sun - partial phase begins
3rd - Moon fully enters Sun - annular phase begins
2nd - Moon starts leaving Sun - annular phase ends
4th - Moon fully leaves Sun - partial phase ends
================================================
PARTIAL SOLAR ECLIPSE
---------------------
1st - Moon starts entering Sun - partial phase begins
4th - Moon fully leaves Sun - partial phase ends
================================================
================================================
TOTAL LUNAR ECLIPSE
-------------------
0th - Moon enters paenumbra - no observable effect
1st - Moon starts entering umbra - partial phase begins
2nd - Moon fully enters umbra - totality begins
3rd - Moon starts leaving umbra - totality ends
4th - Moon fully leaves umbra - partial phase ends
5th - Moon leaves paenumbra - no observable effect
==================================================
PARTIAL LUNAR ECLIPSE
---------------------
0th - Moon enters paenumbra - no observable effect
1st - Moon starts entering umbra - partial phase begins
4th - Moon fully leaves umbra - partial phase ends
5th - Moon leaves paenumbra - no observable effect
==================================================
PAENUMBRAL LUNAR ECLIPSE
------------------------
0th - Moon enters paenumbra - no observable effect
5th - Moon leaves paenumbra - no observable effect
==================================================
The paenumbra is not observable because it is too thin a shadow to
daeke the Moon. The Moon shows no change in brightness, tint, other
quality when she enters and leaves the paenumbra.The inner edge of the
paenumbra, against the umbra, sometimes is darker. causing a shading
on the Moon before 1st and after 4th contact.
Omst astronomers do not count the 0th and 5th contacts in
describing lunar eclipses and some eclipse software pass up paenumbral
eclipses in their calculations.
Ground path
---------
The locations on Earth where an eclipse is visible is plotted as a
broad swath across the globe. it has four sides, curved by the motion
of Sun and Moon a d the curvature of the Earth's surface. The east and
west ends of the path are locations where the eclipse is seen on the
horizon. The west end is for the eclipse at rising; east, setting.
Because of diurnal rotation and eclipse duration the ends are a
zone, sketched here
/--------------------------------\
/| \ /|\
/ | \ / | \
| | | | | |
A| B| C| D E| F| G|
| |===|==========================|==| |
| | | | | |
| | | | | |
\ | / \ | /
\ / \ /
\----------------------------------/
I leave out geography to avoid needless clutter. North is up; /
west, left. The example is for a total or annular solar eclipse with
its center line, '==='. A lunar eclipse has no geographic restriction
on the scene on the Moon.
Observers every where outside the perimeter of the ground path see
no eclipse. Either it is local night or the Moon passes too far north
or south to intersect the Sun.
Observers within the perimeter bu not on the center line see a
partial eclipse. For those north of the center line the Moon passes
over he south side of the Sun; south, north.
Observers closer to the center line see more of the Sun covered at
mid eclipse; father, less.
A is the line where the eclipse ends at sunrise. Observers farther
west see no eclipse. The Sun rises with no Moon on him.
B is the line where the Sun rises in mid eclipse. The Moon is at
her maximum intrusion onto the Sun. Observer here see only the
recession of Moon off of the Sun.
C is the line where the eclipse begins at sunrise. Observers see
the entire eclipse.
D is the largest region of the path where observers see the whole
event in high sky. 'D' is placed near where the eclipse occurs at
local noon, Places between there and C have a morning eclipse; toward
E, afternoon eclipse.
E is the line where the eclipse ends at sunset. Observers here see
the whole eclipse.
F is the line where the sun sets at mid eclipse. Observers see
only the accession of the Moon across the Sun.
G is the line where the eclipse begins at sunset. The Sun sets
before the Moon reaches him. Observers farther east see nothing of the
eclipse.
Eclipses observed within the zones A-B-C or E-F-G of the ground
path are horizon eclipses. New York had its good share of them in
recent years and will have several in coming years.
Horizon lunar eclipse
-------------------
The table here give the horizon lunar eclipses over New York They
span years 2000-2030.
'---' means the contact doesn't exist; it is missing for the
instant eclipse. '' means the contact occurs below the horizon ad is
not visible.
All times are EST. Daylight time is ignored. Times hee may differ
a bit from other sources due to the algorithms used for the
calculations.
-------------------------------------------
date | rise | 1st | 2nd | 3rd | 4th | set
----------- +-------+-------+-------++------+--------+-------
2001 Jan 9 | 16:45 | xxx | xxx | xxx | 16:58 | ---
2005 Oct 17 | --- | 06:34 | --- | ---- | xxx | 06:12
2007 Mar 3 | 17:44 | xxx | 17:48 | 19:00 | 20:13 | ---
2007 Aug 28 | --- | 03:51 | 04:52 | xxx | xxx | 05:22
2014 Oct 8 | --- | 04:17 | 05:27 | xxx | xxx | 06:05
2015 Apr 4 | --- | 05:18 | --- | --- | xxx | 05:39
2018 Jan 31 | -- | 06:52 | xxx | xxx | xxx | 07:07
2021 May 26 | --- | 04:44 | xxx | xxx | xxx | 04:49
2022 Nov 8 | --- | 04:11 | 05:18 | xxx | xxx | 06:41
2026 Mar 3 | --- | 04:559 | 06:09 | xxx | xxx | 06:29
-----------------------------------------------------------
It turns out that most of the lunar horizon eclipses occur at
moonset, in morning dawn.
\
Horizon solar eclipses
--------------------
The table here give the horizon solar eclipses over New York. They
span years 2000-2030.
'---' means the contact doesn't exist; it is missing for the
instant eclipse. '' means the contact occurs below the horizon ad is
not visible..
All times are EST. Daylight time is ignored. Times hee may differ
a bit from other sources due to the algorithms used for the
calculations.
-------------------------------------------
date | rise | 1st | 2nd | 3rd | 4th | set
------------+-------+-------+-------+-------+--------+--------
2001 Mar 14 | --- | 16:19 | --- | --- | xxx | 18:02
2013 Nov 3 | 06:29| xxx | --- | --- | 07:10 | ---
2014 Oct 23 | --- | 16:48 | --- | --- | xxx | 17:04
2021 Jun 10 | 04:21 | xxx | --- | --- | 05:10 | ---
2025 Mar 29 | 05:44 | xxx | --- | --- | 06:04 | ---
---------------------------------------------------------------
It turns out that most of the horizon solar eclipses occur near
sunrise.
All solar eclipses over New York are partial, with no 2nd and 3rd
contact. Some of these eclipses may be total or annular else where in
the world.
Selenehelion
----------
Horizon lunar eclipses can create the wonderful scene of a
selenehelion (seh-leh-neh-HEH-lee=yon). There are two levels of
selenehelion.
The hard or strict one is the simultaneous sight of the Sun and a
lunar eclipse. This naturally requires a horizon lunar eclipse with
timing to be in progress while the Sun is shining at the opposite
horizon. As long as some part of the Moon is obscured by the umbra in
dirct sunlight, it qualifies for a selenehelion. The still with only
the paenumbra on her does not.
Since a lunar eclipse some where is a horizon eclipse, it is
possible, if not practical, to go to a location within the horizon
zone of the eclipse ground path and witness a selenehelion.
A soft or lax one is the simultaneous sight of Sun and any Full
Moon. A Moon in eclipse within the paenumbra, no umbra intrusion, can
be a soft selenehelion for being merely a Full Moon.
This a lax or loose kind because the Moon looks quite full many
hours off of geometric full phase. A limit of tolerance must be
applied for a soft selenehelion, else there can be one for several
days before and after full phase.
The sight of Sun and Moon together is more than pure geometry.
Atmospheric refraction, horizon depression groom high elevation,
looming and miraging can lift the Sun and Moon higher in altitude than
their geometric places. This can trigger a selenehelion in marginal
instances.
One way to record a selenehelion is to photggraph the one body
directly with a mirror reflecting the other into the scene. An other
is to use a true fisheye lens. Yet an other is to photograph the Moon
over a landscape lighted by the Sun.
2021 May 26
---------
In spring of 2021 we have two horizon eclipses. On May 26 at
moonset the Moon enters the umbra right at moonset! Usually in a lunar
eclipse the inner zone of the paenumbra, darker than the rest of the
paennumbra, shows as an orange 'stain' at the point of first contact,
is nominally happens fifteen or so minutes before first contact.. In
this here eclipse the s Moon wis in bright twilight, swamping out this
paenumbra tint.
Will there be a selenehelion? No, because even if first contact
occurs at moonset, the Sun s not yet up and you will not see both Moon
and Sun together.
As a consolation, there is a selenehelion on the previous evening
the 25th near sunset. As the Sun approaches the west horizon the
almost full Moon, getting ready for her eclipse by the next dawn, is
rising.
2021 June 10
----------
Pray really hard for clear sky! On the 10th the Sun undergoes an
annular eclipse. the Moon is too small to fully cover the Sun and,
from Quebec and Canada, a ring of solar disc remains exposed around
the Moon.From New York the Moon crosses off-center over the northern
half of the Sun.
The eclipse begins about an hour before local sunrise. At sunrise
the eclipse is near maximum covering and the Moon is obviously
smaller than the Sun! All the usual projects for observing a solar
eclipse are feasible for this eclipse. Some will be easier or simpler
to construct because the project props and fixtures stand on a
horizontal level.Public viewing could be done in comfort from any
Sun-facing window.
Mind well that at all times in this eclipse substantial portions
of the raw solar disc are exposed. All cautions and protection is
required for safety.
Observing horizon eclipses
------------------------
Apart from preparation for a particular eclipse, there are several
general considerations. There must be a clear sightline into the Moon
or Sun along the horizon. Landscape of little concern for high-sky
observing could block the eclipse, all being less than ten degree
altitude.
From a planetarium software find the azimuth of the body at rise
or set, according to the eclipse, and scout a location providing the
open sightline to that azimuth. Be inventive. Ex[;pre roofs, upper
floor windows, crests, knolls, overlooks, terraces.
Be ready to run against mist and cloud along the horizon, even if
the rest of the sky is clear.
Clouds near the horizon are a severe hazard. They are seen face-
on, overlapping, with probably no clear sky between them. For a deck
ofclouds, even a thin layer can completely block the sun. The path of
sunlight is much longer thru the deck near the horizon than overhead.
The path length is (unit over head thickness)/sin(altitude). At 5 deg
altitude the path is about 11-1/2 times the overhead thickness. At 2
deg it's about 27-1/2. A thin deck letting a zenith Sun shine thru
will totally hide a horizon eclipse.
It may be tempting to view the Sun directly thru haze, it being a
natural filter. Please don't! The density of the haze can shift
without warning. For sure don't look thru the haze with optical
devices Digital devices are safe because the scene is a reconstructed
image on screen, not the directly amplified sunlight. Even so, use
these dives for brief looks to prevent possibly burning out the
electronics.
Earth rotation
------------
we use astronomical events to calibrate ancient chronologies. We
can retrodict a described events to monitor changes in the rotation
of Earth. The Earth is slowing down, making its day length longer as
measured against an atomic clock.if we find an event with a clock hour
recorded, even if roughly, we can compare that hour with the
retrodicted hour. A discordance could be the effect of a faster Earth
in past time. Events are recorded earlier than expected for a constant
rotation of Earth.
A horizon eclipse, regardless of any recorded hour, has a known
observed hour, that of local rise or set of Sun and Moon. The
retrodiction based on today's rotation, is compared to this hour to
mark a datum point in the rotation record of Earth.
This is a sensitive test for rotation. If an eclipse was observed
at local sunrise and described as being just about all over, neat 4th
contact, we know when the eclipse was seen to within a couple minutes.
This is an order more precise than the best timekeeping devices in
early eras. We compute that eclipse for the location of the observer
and find it should have been all over an hour before local sunrise.
When the Sun came up there was nothing about it to indicate an
eclipse. The observers had to learn of the event from travelers and
traders.
Some early horizon eclipses
--------------------------
I observed man horizon eclipses over the ages, some I briefly
describe here.
1959 Oct 2 - My first solar eclipse I traveled from home to
observe. I with several local astronomers set up next to Canarsie Pier
to watch the rising sun across Jamaica Bay. the Sun rose with the Moon
sliding off of him. This eclipse presented a rare feature which I
called 'dawn delayed' but is more commonly today known as 'double
dawn' (double dusk' for a sunset eclipse). During oncoming twilight
totality occurred about five minutes below the horizon. It suddenly
sucked the sunlight from the dawn, turning it back into night! After
totality, as the Sun approached the horizon, sunlight returned and
dawn quickly returned and proceded normally.
1963 Dec 31 - My first horizon lunar eclipse, observed from home.
The eclipse began as dawn broke and totality ended just at moonset.
This was an extremely dark eclipse. I used binoculars to find the Moon
in totality, a task made ever harder as twilight brightened.
q 1975 Nov 18 - Probably New York City's most infamous eclipses. I
with other astronomers watched it from the Empire State Building. The
Moon rose in totality with the usual red hue. News reporters covering
the event with us. The City at that time was facing bankruptcy. When
one reporter asked me what the eclipse means, I noted that this was
the 'Red Ink Eclipse'.
1982 Dec 30 - I with other astronomers observed from a rooftop
apartment on Manhattan. It was more of a social party with the eclipse
as the closing event. Totality ended and the Moon set during the
partial phase.
1986 Apr 9 - I observed this one from Broken Hill, Australia
during a halley's Comet trip. i showed it to the other trippers, who
did 't know about the eclipse. The eclipse was partial from there and
the Sun set with the Moon near maximum coverage.
Conclusion
--------
Eclipses of the Sun and Moon are runaway favorite events for home
astronomers. Most look for locations where the eclipse occurs in high
sky to see the entire spectacle. Horizon eclipses can be an anazingly
beautiful sight.
For New York City most horizon eclipses in 2000-2030 occur at
moonset or sunrise. 4 or the 5 earlier eclipses I observed from the
City also took place in dawn, skipping the Australia eclipse.
I can't find a cause for this. Enjoy the eclipses as they fall out
on the clock. It could be a convergence of eclipse cycles for the late
20th and early 21th century?
An awesome bonus from watching horizon eclipses is the bonding
with our ancestor astronomers. Those skywatchers took note of horizon
eclipses during their duty in society. From their eclipse records we
today keep track of Earth's rotation.