END OF PLEIADES OCCULTATIONS!
---------------------------
John Pazmino
NYSkies Astronomy Inc
nyskies@nyskies.org
www.nyskies.org
2009 November 11 initial
2010 January 17 current
Introduction
----------
In a previous article on the frequency of occultations, I
explained why stars have 'seasons' of occultations. The seasons are
separated by years when the Moon misses the star. For New York City
the last of the Alcyone passes is on 2009 December 28. There after is
a long span of years with no such crossing. In fact, it's the last
chance for the Moon to touch the Pleiades cluster as a whole for the
City! Please read that article as background for this upcoming example
of how the current season for Alcyone is running out.
The article is at 'www.nyskies.org/articles/pazmino/occ-freq.htm'.
Altho Alcyone is not one of the stars discussed, the theory and method
for working up seasons for any star are given.
The information for the present piece comes from computer
simulations and calculations and from various websites relating to
lunar occultations. Among these are Dance of the Planets, Lunar
Occultation Workbench, Occult 4, OccultXZ, International Occultation
Timing Association. Royal Astronomical Society of New Zealand.
Pleiades occultations
-------------------
The Pleiades have about a dozen stars above 6th magnitude that can
be covered by the Moon. The cluster is about 2 degree diameter so it
takes the Moon 3 to 4 hours to cross centrally thru it. As she moves
thru the cluster, she covers and uncovers many of its stars. Published
predictions are usually given for the named stars, skipping the
multitude of dimmer members scattered among them. By a computer
occultation calculator, events for any Pleias may be worked up.
When a star is hidden by the Moon on her forward edge the event is
an ingress, immersion, disappearance. When the star is revealed again
at the rearward edge, it is the reappearance, emersion, egress. All
three terms for each event are commutably used in occultation work.
The long duration of the crossing, the many chances to watch or
show an event, and the conspicuous aspect of the cluster make an
occultation of the Pleiades a favorite show for home astronomers. They
are featured at a public starviewing when ever the hour is convenient,
typicly before midnight.
The brightness of the Pleiades allows occultations to be observed
in poor sky conditions, such as thin cloud and twilight. They can be
seen behind a large Moon, altho the Moon when near full veils some of
the events. With skill, sharp vision, and a large scope events rcan be
observed in daytime.
Pleiades vs Alcyone
-----------------
Alcyone is the brightest member of the Pleiades star cluster, of
magnitude 2.9. It is occulted if the Moon slides across the middle of
the cluster. If she crosses over one corner, she may miss Alcyone, yet
cover other Pleiades members. Predicting occultations of just Alcyone
is NOT the same as predicting for the whole Pleiades. Crossings of
other Pleiades stars may be overlooked because calculations considered
only Alcyone, which in a given instance is missed by the Moon.
This happened on 2009 November 4 (in UT). From New York City the
Moon slided just south of Alcyone in a close miss. She did hit Merope,
Pleione, and Atlas for a good Pleiades show.
Altho most of this discussion applies to Alcyone, the concepts do
apply to the whole Pleiades. For the critical case of the end of the
current season and the beginning of the next, I did look more
carefully at the other Pleiades stars.
The ASCII sketch here shows the named members of the Pleiades.
Among these stars are many others, more being revealed with larger
telescopes. Binoculars bring out a couple dozen stars. North is up;
east, left.
**Asterope
*Taygeta
Maia*
Atlas* *Alcyone *Celaeno
Pleione* *Electra
*Merope
Asterope is the western of the pair of about equal magnitude. The
east one seems to have no proper name. A few refernces cite this pair
as Asterope I (the west star) and Asterope II (east, 22 Tauri).
The names are Greek, very euphonic when properly pronounced. They
using nearest English sounds, are:
---------------------
Pleiades PLAY-a-deez (the whole set of stars)
Pleias PLAY-ass (one of the cluster stars)
Alcyone al-SIGH-oh-nee = eta Tauri, 25 Tauri, ZC 552
Asterope a-STEH-roh-pee = 21 Tauri, ZC 542
(Asterope II) = 22 Tauri, ZC 543
Atlas ATT-lass = 27 Tauri, ZC 560
Celaeno seh-LIGH-noh = 16 Tauri, ZC 536
Electra eh-LEKK-tra = 17 Tauri, ZC 537
Maia MIGH-ya = 20 Tauri, ZC 541
Merope MEH-roh-pee = 23 Tauri, ZC 545
Pleione PLAY-oh-nee = 28 Tauri, ZC 561
Taygeta TIGH-jeh-ta = 19 Tauri, ZC 539
--------------------------------------------
The Bayer/Flamsteed name and the Zodiacal Catalog (ZC) number for
each is given, because the stars may be cited under these names, too.
Note that there are nine named Pleiades stars, altho a normal eye
can discern six and the group is also called the Seven Sisters.
Asterope is sometimes called Sterope (STEH-roh-pee).
A member of the Pleiades is a Pleias. Pleiades is a plural word of
third declension. with Pleias as the singular. It is grammaticly
feminine.
New York va the world
-------------------
Like for solar eclipses there is a gross distinction between
occurrences of occultations and their visibility from a given location
on Earth. Alcyone events during a season take place pretty much every
month, at intervals of a sidereal period of the Moon. Only a few are
actually visible from the City each year because many occur when the
Moon is down.
An occultation occurs if the star's shadow, a cylinder of the
Moon's diameter, sweeps over the Earth. If New York is within the
cylinder, an occultation occurs there. Stated an other way, the discs
of Moon and Earth as seen from Alcyone must overlap over the City or,
at worst, touch by tangency.
The event is seen from the City if the shadow cylinder crosses the
City. From Alcyone, the Moon's disc must hide the City. A miss occurs
if the City is outside of the shadow. This happens if the shadow
simply misses the City or the City is rotated to the far side (from
Alcyone's eye) of the Earth. This puts Alcyone below the City's
horizon.
If the contact is only by tangency, the City experiences a graze
of the star. This happens near the City on 2009 December 28. A brief
occultation of Alcyone is seen near the north limb of the Moon from
within the city. The Mid Hudson Valley, Lower Catskills, Tappan Zee,
Taconics, all about 70km north of the City, get the graze. The star
plays peek-a-boo among the mountains on the lunar north edge.
Current Alcyone season
--------------------
The tables here give the middle of the occultation. This is midway
between the ingress and egress, with Alcyone closest to the center of
the Moon's disc in the sky.
'Lat & Long' is the place on Earth where the Moon crosses
centrally over Alcyone and her local altitude is a maximum. That
altitude is in 'OAl'. At this place and hour the separation between
the Moon and Alcyone, in arcminutes, is in 'SepO'.
For the ideal lat-lon this is zero. Alcyone is centered behind the
Moon. This can happen only if the centerline of the cylinder shadow is
on the Earth. For the last few events the centerline misses the Earth.
For these events the separation is between zero and the lunar radius.
For New York City, the local EST (never EDST) hour is given. Mind
well a step across midnight that can roll the local date back one day.
This hour is NOT the UT shifted to EST. It is the EST hour of maximum
occultation and accounts for the shadow's motion over the Earth.
'SAl' is the Sun's altitude, indicating the sky brightness during
the event. A positive value means it is daytime. 'OAl' and 'SepO' are
like for the ideal location in previous columns.
The season began on 2005 February 16 near the south pole and for
New York on 2006 April 1.
-------------------------------------
Occultations of Alcyone for 2005-2006
---------------------------------------------------------------
Universal Time %SL Lat & Long OAl SepO NYC SAl OAl SepO
----------------- --- ------------ --- ---- ----- --- --- ----
16/02/ 2005 05:35 53+ -60.8 -136.4 0 10* ----- --- --- ----
Start of current season for Alcyone occultations
15/03/ 2005 14:01 29+ -47.4 59.6 15 0* ----- --- --- ----
11/04/ 2005 23:04 11+ -39.1 -113.0 25 0* ----- --- --- ----
09/05/ 2005 07:38 1+ -44.2 93.6 20 0* ----- --- --- ----
05/06/ 2005 14:45 2- -45.4 -39.6 19 0* ----- --- --- ----
02/07/ 2005 20:36 12- -30.9 -159.2 34 0* ----- --- --- ----
30/07/ 2005 02:12 31- -12.5 85.2 52 0* ----- --- --- ----
26/08/ 2005 08:53 53- 2.9 -45.0 68 0* ----- --- --- ----
22/09/ 2005 17:12 74- 10.2 159.0 76 0* ----- --- --- ----
20/10/ 2005 02:49 92- 10.3 -12.4 76 0* ----- --- --- ----
16/11/ 2005 12:15 100- 7.2 179.8 73 0* ----- --- --- ----
13/12/ 2005 20:05 96+ 8.6 35.2 74 0* ----- --- --- ----
10/01/ 2006 02:04 83+ 18.2 -83.6 84 0* ----- --- --- ----
06/02/ 2006 07:38 61+ 31.7 162.5 82 0* ----- --- --- ----
05/03/ 2006 14:43 37+ 41.3 26.1 72 0* ----- --- --- ----
01/04/ 2006 23:55 17+ 42.7 -139.4 71 0* 20:22 -23 23 1*
First Alcyone occultation visible from New York City!
29/04/ 2006 10:03 3+ 39.0 42.8 74 0* ----- --- --- ----
26/05/ 2006 19:25 0- 37.0 -123.8 76 0* 15:45 38 34 2*
23/06/ 2006 02:55 7- 41.6 95.0 72 0* ----- --- --- ----
20/07/ 2006 08:44 24- 52.3 -24.4 61 0* 02:47 -18 26 12*
16/08/ 2006 14:06 44- 61.8 -149.7 47 0* ----- --- --- ----
12/09/ 2006 20:58 67- 66.9 69.6 40 0* ----- --- --- ----
10/10/ 2006 06:05 87- 64.1 -88.1 44 0* ----- --- --- ----
06/11/ 2006 16:52 98- 60.6 99.1 51 0* ----- --- --- ----
04/12/ 2006 03:12 99+ 59.8 -81.9 52 0* ----- --- --- ----
31/12/ 2006 11:23 89+ 68.2 117.1 43 0* ----- --- --- ----
---------------------------------------------------------------------------
Occultations of Alcyone continued in New York regularly since
2006. The City missed many due to the Moon being down. Many were tough
to observe due to daylight.
The series finally runs out with the show of 2009 December 28.
Alcyone events continue in 2010 for other places in the world and
there are a couple events for Atlas and Pleione in early 2011. Then
the season ends for the entire globe.
-------------------------------------
Occultations of Alcyone for 2009-2010
---------------------------------------------------------------
Universal Time %SL Lat & Long OAl SepO NYC SAl OAl SepO
----------------- --- ------------ --- ---- ----- --- --- ----
07/01/ 2009 18:26 83+ 78.4 -20.4 31 0* ----- --- --- ----
04/02/ 2009 02:29 63+ 80.0 158.8 24 0* ----- --- --- ----
03/03/ 2009 08:14 39+ 75.6 94.6 35 0* ----- --- --- ----
30/03/ 2009 13:46 18+ 60.9 3.3 51 0* 07:53 24 2 11*
26/04/ 2009 21:12 5+ 50.9 -127.5 62 0* 17:32 13 36 9*
24/05/ 2009 06:44 0- 48.4 63.9 65 0* ----- --- --- ----
20/06/ 2009 17:10 6- 51.9 -121.7 61 0* 13:23 65 42 11*
18/07/ 2009 02:57 22- 56.6 66.9 57 0* ----- --- --- ----
14/08/ 2009 10:36 43- 53.8 -78.4 59 0* 05:29 3 71 12*
10/09/ 2009 16:28 65- 44.4 172.0 69 0* ----- --- --- ----
07/10/ 2009 21:58 85- 32.3 67.1 81 0* ----- --- --- ----
04/11/ 2009 05:03 97- 24.4 -64.1 88 0* ----- --- --- ----
01/12/ 2009 14:34 99+ 23.9 126.3 89 0* ----- --- --- ----
29/12/ 2009 01:25 90+ 27.2 -64.2 86 0* 20:17 -41 70 16*
Final Alcyone occultation visible from New York City!
25/01/ 2010 11:23 71+ 27.2 119.2 86 0* ----- --- --- ----
21/02/ 2010 18:59 47+ 19.1 -19.7 85 0* ----- --- --- ----
21/03/ 2010 00:41 25+ 5.3 -128.9 71 0* ----- --- --- ----
17/04/ 2010 06:13 8+ -7.7 119.6 58 0* ----- --- --- ----
14/05/ 2010 13:23 0+ -12.5 -13.9 53 0* ----- --- --- ----
10/06/ 2010 22:16 3- -10.5-174.5 55 0* ----- --- --- ----
08/07/ 2010 07:56 16- -8.8 13.2 57 0* ----- --- --- ----
04/08/ 2010 17:00 34- -14.4 -148.7 52 0* ----- --- --- ----
01/09/ 2010 00:25 58- -31.8 76.4 34 0* ----- --- --- ----
28/09/ 2010 06:17 79- -64.8 -26.3 0 5* ----- --- --- ----
25/10/ 2010 11:54 94- -64.6 -135.8 0 15* ----- --- --- ----
00/11/ 2010 --- (Moon misses Alcyone)
19/12/ 2010 03:44 95+ -64.6 -67.3 0 15* ----- --- --- ----
End of current season for Alcyone occultations
------------------------------------------------
The Alcyone occultations for the world end with the event of 2010
December 19, when the shadow cylinder last crosses Earth in the far
south latitudes. It misses New York widely and we see a conjunction
with the Moon passing south of Alcyone. A couple more occultations
occur in 2011 for Merope, Atlas, and Pleione before the season finally
runs out.
Next Alcyone season
-----------------
For the next 13[!] years, the cylinder sweeps south of the Earth,
then edges back north. The first event of the next season is on 2023
September 5 in the far south latitudes. The shadow is creeping north
from beyond the south pole, where it was since 2010.
The first visible occultation for the City is on 2024 September 22
in local dawn thru daytime. The first nighttime event is on 2024
November 16.
-------------------------------------
Occultations of Alcyone for 2023-2024
---------------------------------------------------------------
Universal Time %SL Lat & Long OAl SepO NYC SAl OAl SepO
----------------- --- ------------ --- ---- ----- --- --- ----
05/09/ 2023 20:52 61- -60.7 156.4 0 10* ----- --- --- ----
Start of next season for Alcyone occultations
03/10/ 2023 05:47 82- -60.3 -3.2 0 2* ----- --- --- ----
30/10/ 2023 15:51 96- -60.3 178.9 0 1* ----- --- --- ----
27/11/ 2023 01:24 100+ -60.4 8.4 0 3* ----- --- --- ----
24/12/ 2023 08:52 93+ -62.4 -137.5 0 0* ----- --- --- ----
20/01/ 2024 14:36 75+ -27.8 91.6 37 0* ----- --- --- ----
16/02/ 2024 20:17 52+ -7.6 -25.2 57 0* ----- --- --- ----
15/03/ 2024 03:47 30+ 2.8 -169.6 68 0* ----- --- --- ----
11/04/ 2024 13:29 11+ 4.9 17.4 70 0* ----- --- --- ----
08/05/ 2024 23:51 1+ 2.2 -164.5 68 0* ----- --- --- ----
05/06/ 2024 09:07 2- 2.0 29.5 68 0* ----- --- --- ----
02/07/ 2024 16:22 12- 8.6 -107.5 74 0* ----- --- --- ----
29/07/ 2024 22:00 30- 20.1 138.6 86 0* ----- --- --- ----
26/08/ 2024 03:36 53- 31.1 24.9 83 0* ----- --- --- ----
22/09/ 2024 10:56 74- 36.3 -113.5 77 0* 07:08 15 43 1*
First Alcyone occultation visible from New York City!
19/10/ 2024 20:37 92- 34.7 74.5 79 0* ----- --- --- ----
16/11/ 2024 07:39 100- 31.4 -116.9 82 0* 03:51 -33 40 7*
13/12/ 2024 17:53 96+ 33.1 62.1 81 0* ----- --- --- ----
-------------------------------------------------------------------
Interval between events
---------------------
The interval between occultations is close to the sidereal period
of the Moon, which is the time it takes her to cycle from a given star
back to the star again. The intervals in the tables are irregular. The
Moon has a varying speed along her orbit such that she may run faster
or slower, according to her elongation from the Sun and from her
perigee. The latter was known to the Babylonians; the former, the
Classical Greeks. Hence, the Moon can be ahead of or behind of the
place obtained from her mean motion.
The table here gives the interval between successive occultations
of Alcyone in 2023-2024:
-------------------------
Days between occultations
-------------------------
Universal Time days
----------------- --------
05/09/ 2023 20:52 ---
03/10/ 2023 05:47 27.3716
30/10/ 2023 15:51 27.4194
27/11/ 2023 01:24 27.3979
24/12/ 2023 08:52 27.3111
20/01/ 2024 14:36 27.2389
16/02/ 2024 20:17 27.2368
15/03/ 2024 03:47 27.3125
11/04/ 2024 13:29 27.4042
08/05/ 2024 23:51 27.4320
05/06/ 2024 09:07 27.3861
02/07/ 2024 16:22 27.3020
29/07/ 2024 22:00 27.2343
26/08/ 2024 03:36 27.2333
22/09/ 2024 10:56 27.3056
19/10/ 2024 20:37 27.4034
16/11/ 2024 07:39 27.4598
13/12/ 2024 17:53 27.4263
----------------- -------
average 27.3456
--------------------------
On the other hand, the shift of phase, indicated by the percent
illuminated (%SL column) is more stable. For the short periods of
these tables, the phase cycles in 13 months. This is how long it takes
the the offset of solar and sidereal period, about 2.2 days, to
accumulate to a whole phase cycle. This, too, is a bit irregular.
Not demonstrated here, but fully detailed in the occultation
frequency article, is the 'rule-of-19'. It's the same as for solar or
lunar eclipses. Given the date of one occultation, there is an other
of the same phase and hour exactly 19 calendar years later or earlier.
What a wait!
----------
After the Pleiades show of 2009 December 28, the City has a LONG
wait for the next one on 2024 September 22. The Moon swings south of
the cluster in the sky until then.
At the southern limit of her excursion, she can cross the
companion cluster in Taurus, the Hyades. She can also hit Aldebaran,
not a cluster member but within its confines by line up.
Earth's first Aldebaran occultation of the next season, we now
already being between seasons for this star, is on 2015 January 29.
No, New York doesn't see that one because the shadow is too far
north of us. Our own next event is on 2015 September 5 at night. There
after, we get Aldebaran events every couple months.
So!, if you want to see a Pleiades occultation from the City, THE
2009 DECEMBER 28 SHOW IS YOUR LAST CHANCE FOR ONE HELL OF A LONG TIME.
Hope for clear skies!
2006 April 1
----------
The tables below give the circumstances of each Pleias for a mid
point within New York City. These differ substantially for observers
far from this point.
The percent illumination is the disc fraction lighted by the Sun.
A '+' value means the Moon is waxing between new, thru 1st quarter, to
full; '-', waning, full, 3rd quarter, to new.
The elongation is the distance along the ecliptic from the Sun,
either east or west.
The librations in longitude and latitude give the orientation or
facing of the lunar globe toward Earth. The values are the
selenographic longitude and latitude of the center of the disc. They
are important for figuring out the profile of the Moon with its
mountains and valleys along the limb where the stars are covered and
uncovered.
'Alt-az' are the altitude and azimuth of the Moon at each event.
If the Sun is above the horizon for the event, its altitude is noted
in an extra column for Sun. Cusp, pos, ver are the three angles
expalined above.
'Cusp', the cusp angle, is the place on the lunar limb from the
north or south cusp and round the lighted or dark side. An angle of,
say, +45S means the star touches the Moon 45 degrees around on the
dark side of the lunar limb from the south cusp. One of -60N means the
star is 60 degrees around on the bright side from the north cusp. The
cusp angle can not be more than 90 degrees because it will then be
counted from the opposite cusp. For a moon near full phase the cusp
may be blunt and hard to fix.
'Pos', the position angle, is the angle counterclockwise around
the lunar edge from the celestial north point. This is not the north
pole of the Moon or the north point relative to the ecliptic. It's the
point along the direction to the north celestial pole, in lime with
the right ascension of the Moon. This angle may be the one to use when
tracking the Moon with an equatorial mount.
'Ver', the vertex angle, is the counterclockwise angle counted
from the apex, top, point of the disc. It's the point along the line
to the zenith. It may be the better angle for an alt-azimuth mount or
handheld optics.
The first occultation of Alcyone for New York in this current
season was on 2006 April 1. It occurred in late night In this table
EST, not EDST, is listed. The Moon just misses Celaeno and Maia from
the City. Places a few tens of kilometers south of the City saw a
graze, where the Moon just barely touched the stars at the north
cusp.
--------------------------------------------------------
Moon 16% illum, 47d E elon, lib lon +5.8d, lib lat -5.3d
-----------------------------------------------------------
EST Event Alt-Az Cusp Pos Ver comments
----- --------------- ------ ---- --- --- --------------
18:20 Sun sets 45 264 -- --- --- 3.6 day old
18:41 Electra ingress 41 268 +75N 59 2
18:48 civil dusk 40 268 -- --- ---
19:15 Celaeno miss 35 274 +6N 350 293 off north cusp
19:21 Merope ingress 34 274 +55S 109 53
19:21 nautical dusk 34 274 -- --- --- full night in City
19:44 Maia miss 30 278 +7N 351 295 off north cusp
19:44 Electra egress 29 278 -63N 280 225
19:52 Alcyone ingress 28 279 +80S 84 28
20:17 Merope egress 23 282 -+69S 233 179
20:37 Pleione ingress 20 285 +74S 90 36
20:38 Atlas ingress 20 285 +56S 108 55
20:53 Alcyone egress 17 287 -84N 260 207
21:30 Atlas egress 11 293 -73S 237 187
21:34 Pleione egress 10 293 -89N 256 206
22:39 Moon sets 0 302 -- --- ---
-----------------------------------------------
This is not the first PLEIADES occultation for the City! On 2006
Jan 10 the Moon crossed Atlas, Merope, Pleione, but not Alcyone. The
Moon didn't reach far enough north to touch Alcyone. The distinction
between Alcyone, only ONE Pleias, and the whole group of Pleiades is
crucial
New York's occultations
---------------------
New York is well favored by this current round of Pleiades shows.
The table here gives the date, in UT, of each of the shows in New York
and the stars hit by the Moon, marked 'X'.
Under 'sky' is the skylight. If any part of the event was in dawn
or dusk, this is noted. If the Sun was up for the whole show it
occurred in daytime, 'day'. Else the show was in nighttime, 'dark'. A
dawn event could progress into daytime; dusk, into nighttime.
In each year of 2006 thru 2009 the City enjoyed 5 to 7 of Pleiades
occultations. Some were in daytime, when they are hard to observe.
Most home astronomers skip these.
If we stay with only the nighttime shows, the City still had 2 to
5 chances each year. It's not surprising that a newcomer to astronomy
can soon get jaded by this frequency of a beautiful celestial show.
+-------------+------+---+---+---+---+---+---+---+---+---+
| date (UT) | sky |Alc|Ast|Atl|Cel|Ele|Mai|Mer|Ple|Tay|
+-------------+------+---+---+---+---+---+---+---+---+---+
| 2006 Jan 10 | dark | | | X | | | | X | X | |
| 2006 Apr 2 | dusk | X | | X | X | X | | X | X | |
| 2006 Jul 20 | dark | X | | X | | | | X | X | |
| 2006 Aug 16 | day | | | | | | X | | | X |
| 2006 Oct 10 | dark | | X | | X | X | X | | | X |
| 2006 Dec 4 | dark | | | | X | X | X | | | X |
+-------------+------+---+---+---+---+---+---+---+---+---+
| 2007 Feb 23 | day | | | | | | | | | X |
| 2007 Apr 19 | day | | | | | X | X | | | X |
| 2007 Jun 13 | day | | | | | X | X | | | X |
| 2007 Sep 3 | dark | | X | | | | | | | X |
| 2007 Oct 27 | dark | X | | | | X | X | | X | |
| 2007 Dec 21 | day | X | | | | | | | | |
+-------------+------+---+---+---+---+---+---+---+---+---+
| 2008 Jan 18 | dark | | X | | | | | | | X |
| 2008 Mar 12 | day | | | | | | X | | | X |
| 2008 Apr 9 | dark | | X | | X | | X | | | X |
| 2008 Jun 30 | dark | X | | | X | | X | | | |
| 2008 Sep 20 | dark | X | | | X | X | X | | | X |
| 2008 Oct 17 | dawn | | | | X | | X | | | X |
| 2008 Dec 11 | dark | | X | | X | | X | | | X |
+-------------+------+---+---+---+---+---+---+---+---+---+
| 2009 Feb 4 | dark | | X | | | | | | | X |
| 2009 Mar 30 | day | X | | X | | | | | X | |
| 2009 Apr 26 | day | X | | X | | X | X | | | X |
| 2009 Jun 20 | day | X | | X | | X | X | | X | X |
| 2009 Aug 14 | dawn | X | | | X | X | X | | | |
| 2009 Nov 4 | dark | | | X | | | | X | X | |
| 2009 Dec 29 | dark | X | | X | | | | X | X | |
+-------------+------+---+---+---+---+---+---+---+---+---+
The Moon can not in a given instance cover all of the named stars
of the Pleiades. They are dispersed beyond the Moon's angular
diameter. Usually the Moon hits the stars in two groups. Asterope,
Celaeno, Electra, Maia, and Taygeta are the west group. Alcyone,
Atlas, Merope, and Pleione are in the east group.
2009 December 28
---------------
This ocultation occurs in evening between Christmas and New Year.
This is the very LAST covering of the Pleiades by the Moon for New
York until 2024! Occultations resume with the dawn event on 2024
September 22.
Alcyone suffers a brief covering over the City. Places to the
north see a graze event.
---------------------------------------------------------
Moon 90% illum, 143d E elon, lib lon -6.0d, lib lat -5.0d
-----------------------------------------------------------
EST Event Alt-Az Cusp Pos Ver comments
----- --------------- ------ ---- --- --- --------------
13:30 Moon rises 0 58 -- --- --- 11.4 day old
16:36 Sun sets 31 85 -- --- ---
17:07 civil dusk 37 90 -- --- ---
17:44 nautical dusk 44 96 -- --- --- full night in City
19:09 Merope ingress 59 114 +36N 28 78
20:03 Merope egress 68 134 -55N 297 334
20:07 Alcyone ingress 68 135 +7N 359 36
20:18 Alcyone graze 69 139 -9N (69km away in azim 338deg)
20:28 Alcyone egress 71 147 -24N 328 356
20:32 Atlas ingress 71 148 +58N 51 77
20:44 Pleione ingress 72 156 +38N 31 50
21:15 Moon culminates 73 180 -- --- ---
21:41 Pleione egress 73 201 -51N 302 285
21:45 Atlas egress 72 204 -71N 282 262
00:00 midnight 53 256 -- --- ---- Dec 28 -> Dec 29
-----------------------------------------------------------------
Please mind the timezone! Sources may say this occultation occurs
on December 29. It does occur on that dte in GMT. Most calculations
are done in GMT and, optionally, shifted to the timexone of the
observer. In the case of New York this makes the date December 28.
It happens that this is BOTH the last Alcyone AND last Pleiades
event for the City in this season. This congruence is only by chance.
It could well have worked out that the Moon crosses the eastern stars
of the cluster in 2010 while missing Alcyone.
2024 September 22
---------------
This is the first of the new season of Alcyone occultations for
New York after the one of 2009 December 28. Altho it is a dawn thru
day show, astronomers will probably make special effort to observe it
to welcome the new series of occultations.
It is possible that in the 2020s new observing devices and methods
may be in the hands of home astronomers to allow casually seeing stars
in daylight. There may no longer be a distinction between an
occultation in day from that in night.
Already home astronomers can avail of remote observatories
situated in nighttime places when it is day in the City. Soon they may
work with spacebased observatories. These are not valid for
occultations whose events are calculated specificly for New York.
Specialized computations are needed for the spacebased platforms
because they are in constant motion relative to the Moon's shadow
cylinder.
The regime of daylight savings time in 2024 is uncertain, due to
its capricious alteration by legislation. Here I use Eastern Standard
Time. There is no credible prediction of deltaT, the divergence
between atomic time by which the predictions are calculated, and the
observed universal time (or zone time). The value for 2009, about 74
seconds, is extrapolated linearly. The actual times on the future
clock, in UT or EST, may be off by a full minute.
The geographic location of the City is assumed constant with no
displacement by tectonics, earthquakes, rising sea levels.
----------------------------------------------------------
Moon 75% illum, 128d W elon, Lib long +6.0d, Lib lat -5.3d
-----------------------------------------------------------
EST Event Sun Alt-Az Cusp Pos Ver comments
----- --------------- --- ------ ---- --- --- --------------
03:31 Moon culminates -- 73 180 -- --- --- 21.7 day old
04:44 nautical dawn -- 68 559 -- --- --- end of night
05:16 civil dawn -- 63 239 -- --- ---
05:17 Electra ingress -- 63 240 -53N 38 351
05:43 Sun rises 0 58 247 -- --- ---
05:50 Merope ingress 1 57 250 -71S 94 43
06:18 Electra egress 6 52 257 +55N 290 236
06:29 Alcyone ingress 8 51 259 -89S 76 21
07:00 Merope egress 13 44 265 +73S 238 182
07:21 Atlas ingress 17 41 268 -60S 106 49
07:39 Alcyone egress 21 37 271 +86N 260 203
08:20 Atlas egress 28 30 277 +69S 234 179
11:24 Moon sets 43 0 303 -- --- ---
---------------------------------------------------
Viewing an occultation
--------------------
No special preparation, other than being alert and attentive, is
needed to watch an occultation. Just about any optic that clearly
shows the star near the Moon's limb will do. It is helpful if the
scope can track the star, like by an equatorial mount, but a smoothly-
adjustable alt-azimuth telescope is adequate.
Go out about 15 minutes before the star's immersion or emersion to
orient yourself in the sky and make sure you're looking at the right
star and spot on the lunar disc. Understand that the Pleiades and Moon
will seem to rotate clockwise over the hours due to the way the earth
points New York toward them in space.
A minute or so before the event, it is important to remain calm
and relaxed If feasible, be seated at the telescope, not hunched over
or contorted around it. Guard against distractions like wind and
lights in the eyes. Put down any items in your hands, such as drinks,
maps, tools.
For an ingress you ride the star to the lunar edge, where it
suddenly snaps out of view behind the Moon. This event is now over.
For an egress you have to be focused on the point where the star will
emerge from behind the Moon. Pay close attention to the sense of the
angles, marking them on a moon map. The star pops into view without
warning. any subtile distraction, like an eye blink, will cause you to
miss the instant of reappearance. You first see the star a second or
so later edging away away from the Moon with clear sky between it and
the disc.
Predictions are usually published to the second of time, the
Moon's motion being quite well established by now. In the tables for
this article I deliberately truncated the seconds, showing the hours
to the previous minute. This gives a few seconds leadtime to
anticipate the event. If I rounded the minutes, the hour could fall
AFTER the event!
Geographic circumstances
----------------------
Occultations are visible where ever the shadow of the Moon,
thrown by the star, crosses the observer. However, the circumstances
of the occultation for each observer is a strong function of the exact
path of the shadow over him. Thus, while I write here of the situation
for New York City, the data are really not easily transferible to
other towns without fancy computations.
As an example of how different the Pleiades occultation looks from
various US towns, the table here shows the 2009 December 28 event. To
make comparison among towns easier, I removed the timezone offsets to
leave the hours in UT, or GMT.
In this peculiar case, the date in UT is December 29th. In other
words, while it is evening on the 28th in the US, it's the next
morning the 29th in Greenwich, England.
I tabulated just the immersions. The star can be followed on its
way to the lunar disc before it slides behind the Moon. A similar
table could be compiled for the egress events.
Predictions for any location is obtainable thru computer software or a
local astronomy center.
A glance thru the table shows that not all stars are hit by the
Moon from a given town. the '---' means the Moon misses the star, in
this instance by passing too far south of it. A star can be skipped
also because it is covered when the Moon is still below the horizon.
------------------------------------------------------
TIMES (UT, GMT) OF IMMERSION OF NAMED PLEIADES STARS
ON 29 DECEMBER 2009 FOR VARIOUS UNITED STATES TOWNS
------------------------------------------------------
town |Merope |Alcyone |Atlas |Pleione
------------------+--------+--------+--------|--------
Anchorage AK | --- | --- | --- | ---
Atlanta GA | --- | 00:23 | 01:04 | 01:12
Boston MA | --- | 01:23 a| 01:40 | 01:53
Brownsville TX | 23:23 b| 00:05 | 00:35 | 00:42
Chicago IL | --- | --- | 01:20 | ---
Dallas TX | --- | 00:36 a| 00:49 | 01:01
Denver CO | --- | --- | 01:11 | ---
Detroit MI | --- | --- | 01:25 | 01:44
Fairbanks AK | --- | --- | --- | ---
Juneau AK | --- | --- | --- | ---
Kansas City MO | --- | --- | 01:07 | ---
Los Angeles CA | --- | --- | 01:03 a| ---
Memphis TN | --- | 00:47 a| 01:00 | 01:11
Miami FL | --- | --- | 01:03 | 01:05
Minneapolis MN | --- | --- | 01:28 | ---
New Orleans LA | --- | 00:17 | 00:50 | 00:57
New York NY | 00:08 | 01:07 | 01:32 | 01:44
Oklahoma City OK | --- | --- | 00:56 | 01:11
Philadelphia PA I 00:03 | 00:56 | 01:27 | 01:38
Phoenix AZ I --- | --- | 00:52 | ---
Salt Lake City UT I --- | --- | 01:18 a| ---
San Francisco CA | --- | --- | --- | ---
Seattle WA | --- | --- | --- | ---
St Louis MO | --- | --- | 01:08 | 01:24
Tampa FL | --- | 00:12 | 00:58 | 01:02
Washington DC | 00:01 | 00:55 | 01:24 | 01:35
------------------+--------+--------+--------+--------
a - very close miss
b - on December 28
------------------
The times for New York are slightly different than the ones in the
detail table above. This is due to both rounding and use by a slightly
different lat-lon for the City.
The Moon courses thru the stars from west to east, so the Pleiades
are covered earlier for the western towns. Far northern towns miss the
occultations because they see the Pleiades over the Moon's north edge,
the globe passing too far south of the stars.
In general, towns in Mountain time see the occultation in dusk.
Those in Pacific time see it in daylight near sunset.
Alcyone graze
-----------
From places north of the City the Moon just nicks Alcyone, letting
it play peek-a-boo in the hills and dales on the north edge of the
Moon. For places along the longitude of New York the graze is at 20:18
EST. The scene is somewhat like this ASCII sketch:
>-- motion of Alcyone relative to Moon -->
#---------/-hills interrupt Alcyone
## ### #--/
* * * * * ### * ####*####* ###* * * * --path of Alcyone
####### ################ ##
#############################--Profile of lunar limb
#################################
Understand that altho this Alcyone event is part of the closing
Pleiades show, grazes of other bright stars occur continually in every
year. The specific stars vary from year to year, but there are always
an opportunity in the next couple months.
The coordinates below are points along the ground track of the
graze. These span 72 to 76 degrees west longitude. Plot them on a
large-scale topographic or computer GIS map.
For short distances, a few tens of kilometers, the plot is nearly
a straight line on the map. This line is the northern edge of the
swath painted by the Moon's shadow over the ground. It is determined
by the combined rotation of the Earth under the shadow and the
shadow's motion over the Earth's globe.
Places a little SOUTH of this line see a regular occultation, a
brief one of many seconds or a minute. Places a little NORTH see a
very close miss. The Moon doesn't touch the star at all.
A parallel limit delineates the southern edge of the shadow swath.
This is about 4,000 kilometers south of New York, based on the
diameter of the Moon, and is of no concern for us in the City area. A
graze limit for a given location is either a northern or a southern
limit. The other one is way too far for easy access.
----------------------------------------------
2009 Dec 29 1h 13m UT to 2009 Dec 29 1h 22m UT
--------------------------------------------------
Longitude Latitude Hour EST Moon Pos Cusp
--------- -------- -------- ------- ----- -------
d m s d m s h m s Alt Az deg deg
--------- -------- -------- ------- ----- ------
-76 0 0 40 45 31 20 14 34 68 134 343.4 -9.07N
-75 45 0 40 50 39 20 15 2 69 135 343.4 -9.00N
-75 30 0 40 55 45 20 15 31 69 136 343.5 -8.94N
-75 15 0 41 0 46 20 15 59 69 137 343.6 -8.87N
-75 0 0 41 5 45 20 16 27 69 138 343.6 -8.81N
-74 45 0 41 10 40 20 16 55 69 139 343.7 -8.74N
-74 30 0 41 15 32 20 17 24 69 140 343.8 -8.67N
-74 15 0 41 20 21 20 17 52 69 141 343.8 -8.60N
-74 0 0 41 25 6 20 18 20 69 142 343.9 -8.54N
-73 45 0 41 29 48 20 18 48 69 143 344.0 -8.47N
-73 30 0 41 34 27 20 19 15 70 144 344.0 -8.40N
-73 15 0 41 39 3 20 19 43 70 145 344.1 -8.34N
-73 0 0 41 43 35 20 20 11 70 146 344.2 -8.27N
-72 45 0 41 48 5 20 20 39 70 147 344.3 -8.20N
-72 30 0 41 52 31 20 21 6 70 148 344.3 -8.13N
-72 15 0 41 56 53 20 21 34 70 149 344.4 -8.06N
-72 0 0 42 1 13 20 22 1 70 149 344.5 -7.99N
-----------------------------------------------------
To see Alcyone flit among the lunar mountains, you must be ON THIS
LIMIT LINE within a couple hundred meters. The scene you experience is
a sensitive function of your exact location, exact profile of the
Moon, precision of the Moon's orbit, and precision of the star's
position in the sky. Get any one of these wrong and you may miss a
good graze show.
The hour is the geometric contact of Alcyone with the mean
circular edge of the Moon, ignoring any relief around it. The actual
start of the event, the instant of the first ingress, could be many
seconds earlier or later. There after, Alcyone pops in and out of
sight as each mountain or valley passes over it.
Preparing for a graze
-------------------
Preparation for a graze is more rigorous than for a total
occultation because you must be at the very edge of the cylinder
shadow when it rushes over you. In addition, you have to be alert and
attentive for many minutes while the star pops in and out of sight
around the contours of the Moon's limb.
Scout out a location a couple days before the event. Do NOT plan
to find a viewing spot on the evening of the event! Look around by day
and then visit, after obtaining permission, at night to make sure you
know your way to and from the site.
For a first-cut selection of places near the graze limit, I list
here towns between 72 and 76 degrees west longitude within 100km of
the limit.
Distances of sample towns from Alcyone north graze limit
--------------------------------------------------------
Site Long. Lat. Dist. h m s
-------------------- ----- ---- ------ --------
Bridgeport CT -73.2 41.2 51km S 20 19 50
Central Islip LI -73.2 40.8 91km S 20 19 49
Elizabeth NJ -74.2 40.7 71km S 20 17 55
Hartford CT -72.7 41.8 5km S 20 20 46
Holyoke MA -72.6 42.2 38km N 20 20 54
Jersey City NJ -74.1 40.7 69km S 20 18 12
Meriden CT -72.8 41.5 26km S 20 20 34
New Britain CT -72.8 41.7 13km S 20 20 35
New Haven CT -72.9 41.3 46km S 20 20 19
New York NY -74.0 40.8 69km S 20 18 20
Newark NJ -74.2 40.7 64km S 20 18 0
Paterson NJ -74.2 40.9 46km S 20 18 0
Pittsfield MA -73.3 42.4 82km N 20 19 43
Reading PA -75.9 40.3 45km S 20 14 42
Scranton PA -75.7 41.4 54km N 20 15 12
Springfield MA -72.6 42.1 27km N 20 20 56
Stamford CT -73.5 41.1 52km S 20 19 11
Trenton NJ -74.8 40.2 97km S 20 16 53
Waterbury CT -73.0 41.6 17km S 20 20 6
White Plains NY -73.8 41.0 47km S 20 18 46
Wilkes Barre PA -75.9 41.2 45km N 20 14 47
Yonkers NY -73.9 40.9 53km S 20 18 31
-------------------------------------------------------
Be SURE to obtain positive permission to view from private
property. Apply at the managing agency for viewing from public land.
Be aware that some parks and fields close at night or in the winter.
If you view from a roadside, set up about 10 meters away from the
traffic lanes. This lessens your attraction for badniks to throw
bottles, play with firearms, or stop and pester you.
Obey all rules and instructions of the property manager. Remove
all litter and restore all disturbance you produce. Leave gates in the
setting you find them, whether open or closed. Report suspicious
activity or hazardous conditions to the property manager.
Do NOT intervene into activity of strangers! Observe them from a
safe distance, leave quietly, report the incident to the property
manager or police. Have your own permission papers to hand.
Pay close attention to transit schedules. Service can fall off
drasticly at night. Have a pick-up phone number handy. This may be for
family, friend, taxi service.
Have a charged-up cellphone and rescue phone numbers with you.
Pack extra clothes for the winter weather if you are away from heat
and shelter.
Other clusters
------------
The Moon can cross other star clusters and some nebulae besides
the Pleiades. Only one other gives a spectacular show, the Hyades. All
of the others are either made of dim stars veiled by a bright near Moon
or are diffuse targets with no firm contact instant.
Predictions for these other targets are not widely circulated but
can be calculated individually by computer software. The Hyades stars
like those of the Pleiades, are individually computed.
The Moon passes thru the Virgo field of galaxies but none of them
is readily visible close to the Moon. On the other hand, if you
observe in radio bands, the Moon's covering and uncovering of a radio
source is noted by the instant cutoff and return of signal. The Crab
nebula (M1) and the quasar 3C273 are traditional examples of radio
targets along the Moon's path.
Clusters and nebula near the ecliptic occultable by the Moon
include:
------------------------------------------
Cluster and nebulae occultable by the Moon
------------------------------------------
Name RA (2000) Dec Cns Mag Comments
------ ------------ --- --- --------
Hyades 04 27 +16 00 Tau 0.5 individual stars
N1647 04 46 +19 04 Tau 6.4
N1746 05 04 +23 49 Tau 6.1
N1750 05 04 +23 39 Tau 6.1
N2168 06 09 +24 20 Gem 5.1 M35
N2175 06 10 +20 19 Ori 6.8
N2632 08 40 +19 59 Cnc 3.4 M44, eps Cnc
N2682 08 50 +11 49 Cnc 6.9 M67
N6093 16 17 -22 59 Sco 7.3 M80
N6121 16 24 -26 32 Sco 5.8 M4
N6494 17 57 -19 01 Sgr 5.5 M23
N6514 18 02 -23 02 Sgr 6.3
N6531 18 05 -22 30 Sgr 5.9 M21
N6530 18 05 -24 20 Sgr 4.6 M8
Cr367 18 10 -23 59 Sgr 6.4
N6603 18 18 -18 25 Sgr 3.1 M24
I4725 18 32 -19 15 Sgr 4.6 M25
Cr394 18 54 -20 23 Sgr 6.3
----------------------------
Except for the Hyades, and possibly epsilon Cancri (M44, the
Beehive cluster), none of these targets is easily observed when close
to the Moon. Substantial skill and keen eyesight are required, as well
as a Moon well away from full phase.
Conclusion
--------
Occultations of stars by the Moon are a favorite and frequent
event in the sky. The more showy events, like those of the Pleiades,
make for public viewing sessions over a several hour span.
Since 2006 New York enjoyed repeated passes of the Moon across the
Pleiades, but now the game is over. After this final show on 2009
December 28 (in EST), the Pleiades are missed by the Moon for the next
14 years!
There will be other occultations almost as spectacular as those of
the Pleiades, notably those of the Hyades starting in the mid 2010s.
Of all of the other targets, both clusters and nebulae, none are
really good performers when approached by the Moon. They are too
easily veiled by even a modestly lighted Moon.
Hence, this Pleiades occultation of December 28th is really the
last chance for a spectacular celestial hide & seek for one hell of a
long time to come.