OCCULTATION OF SATURN, 2014 AUGUST 31
--------------------------------
John Pazmino
NYSkies Astronomy Inc
nyskies@nyskies.org
www.nyskies.org
2014 August 16
Introduction
----------
The Moon occults, covers, crosses in front of, planet Saturn on
2014 August 31 Sunday in early afternoon over New York City. This
event occurs in full daylight with Sun in high sky and Moon in the
east. For new York te coverage lasts about 1/2 hour wit Saturn
entering on the dark, invisible, side of the Moon and leaving on the
bright side. The Moon is a waxing crescent, usually easily seen in
daylight.
Occultations of planets by the Moon are an amazing sight! The
planet's disc, and rings for Saturn!, take many seconds to sink into
the lunar globe. It takes a comparable time to emerge from behind the
Moon at the end of the occultation.
Many home astronomers think that planet occultations are rare.
Most can recall seeing only one or two in their entire astronomy
career. We learn below that planet occultations aren't all that rare
but many are tough to observe.
Occultation from New York
-----------------------
Calculations were made by Occult-4 for a central site within the
City, The time at other nearby sites is a few seconds to a minute off.
In general places west of the City see the events earlier; east,
later. Prepare to view the occultation fifteen or more minutes before
the listed time.
The specs of the Saturn event are in the table below. The columns
are:
* UT date and hour. This is four hours AHEAD of EDST.
* Phase: D for disappearance, immersion, ingress. R for
reappearance, emergence, egress
* The occulted star , Sat' for planet Saturn
* Percent illumination of Moon. + for waxing, - for waning
* Elongation of Noon from Sun on ecliptic: + for east; -, west
* Sun altitude for the event in daylight or twilight
* Moon altitude and azimuth for the event
* Cusp angle from N or S cusp along limb, - for bright, + for dark
* Position angle CCW around limb from celestial north
* Vertex angle CCW around limb from instant zenith or top of limb
* Libration angle for lon L and lat B, lon-lat of center of disc
-----------------------------------------------------------------
Occultation prediction for New York NY
East Lon -73 59 42.0, Lat +40 45 06.0; Alt 17m
----------------------------------------------
UT Day & Time P Star Mag %Ill Eln Sun Alt-Az Cusp Pos Ver LibL LibB
--------------- - --- --- ---- --- ------ ---- --- --- ---- ----
Aug 31 17 26 17 D Sat 0.6 32+ 69 57 12 122 34N 50 91 -6.2 -2.6
Duration of planetary disk occultation: predicted time +/-33.4 secs
Aug 31 18 1 41 R Sat 0.6 33+ 70 55 18 129 -26N 349 27 -6.3 -2.6
Duration of planetary disk occultation: predicted time +/-35.3 secs
---------------------------------------------------------------------
Mind well that the ingress is on the dark limb, which is
completely blended into the daytime sky. The planet will suddenly
start to 'eat away' with no apparent cause. The egress is near the
north cusp on the bright limb a half hour later
The vertex angle is useful for a telescope on on alt-azimuth stand
lined up with geographic north. The position angle is for equatorial
scopes properly lined up to the celestial pole.
A regular scope, magnifying 30 or so times is really required. ou
miss the whole show of the rings and globe merging into the Moon.
Here is a timetable for August 31. The hour are EDST being that
August in New York suffered under EDST, one hour ahead of RST.
----------------------------------------
EDST event | alt-az | remarks
------+----------------+--------+--------
05:24 | nautical dawn | -- --- | end of full night
05.55 | civil dawn | -- --- | start of daytime work
06:23 | Sun rises | -- --- | start of daylight, azm 79d
12:07 | Moon rises | 00 110 |
12:12 | Saturn rises | 01 111 |
12:56 | Sun cuminates | 08 119 | local solar noon, alt 58d
13:26 | Saturn ingress | 12 122 |
14:02 | Saturn egress | 18 129 |
17:21 | Saturn culmin | 33 178 | alt 34d
17:26 | Moon culminate | 33 180 |
19:28 | Sun sets | 27 212 | end of daylight, azm 281d
19:56 | civil dusk | 27 218 | end of daytime work
20:29 | nautical dusk | 20 225 | start of full night
22:28 | Saturn sets | 01 247 |
22:35 | Moon sets | 00 248 |
--------------------------------------------------
Graze occultation
---------------
Saturn passes behind the Moon close to her north cusp. Some 250
kilometers north of the City Saturn grazes the Moon's north cusp.
He skips behind mountains on the lunar limb like a spaceship doing a
touch-&-go pass!
If you are favored to visit family or friends north of New York,
inquire at area astronomy centers about this graze occultation.
Planet occultations
-----------------
. Unlike an occultation of a star, that of a planet is far more
complex to calculate. Both Moon and planet move thru the zodiac. Doing
the calculations by hand was a hideous chore, taking a whole weekend
with a mix of maths and graphs. Today a planet occultaiton can be
computed thru astronomy softwares. This may be a general purpose
planetarium or a dedicated occultation tracker.
Occult-4, as one example, searches for planet events along with
those for stars. Dance of the Planets, has a specific feature to hunt
up planet occultations. The better planetarium software accurately
simulate planet occultation for a given instance.
The phase of occultation computed differs among software authors.
Some bank off of the center of the planet's disc while others compute
the tangent points of the event. Since you are ready to observe
fifteen or more minutes in advance of the ingress, the few seconds
discrepancy among calculations doesn't matter.
A few authors include the events of the ansae of Saturn's rings.
In this article the rings are omitted. They touch the Moon at ingress
about 30 seconds before the ball and fully break free at egress some
30 seconds after the ball.
Saturn on the limb
------------- --
When the planet is adjacent to the Moon you notice that the one or
the other is 'brighter'. A tiny angular area of one shines with
greater illumination than the same area of the other. This is due to
the different reflective efficacy, sending more or less sunlight, of
each. This comes from the different surface composition and texture of
the two bodies.
Surface brightness is commonly cited in stellar magnitude per
square arcminute or arcsecond. This is also called, more photometricly
correct, the angular illumination. For the full Moon this is -5.0
magn/min2 on the average.
More over, the surface brightness of the Moon varies widely with
phase, being far greater near full than in crescent phase. The
difference is not simply the portion of shadowed to lighted areas, but
the angle of sunlight at the limb of the Moon, the local hour of the
lunar day, and the thick tunic of pulverized material on the ground.
Because the planet at the lunar limb spans a significant linear
extent on the Moon, most authors do not bother with applying limb
correction. This is done for a star, being a point, that can hit the
limb at a mountain or valley.
Libration is applied, which orients the triaxial lunar globe to
place the proper spot of 'sea level' limb at the planet.
Public viewing
------------
The NYC Events column for August 2014 will list any public
viewing for this event, if any are announced to NYSkies in time for
publication at end of July. For locations wanting of listed
occultation sessions, please call on the astronomy center in the
vicinity for last minute news. Use the contact given for the center's
other events in August.
August 31st is sUnday, which could ease the problem of arranging
for a viewing site away from the normal night viewing sessions. Each
host facility has its own practice and procedure for letting astronomy
groups use its premises. Permission obtained by the group on an earlier
occasion can not promise a repeat permission for this occultation.
Weather
-----
The greatest impediment against seeing this occultation is
weather. August in New York is when the Sun and Sirius commingle their
rays at sunrise to make the Dog Days. Expect oppressive heat,
specially if you must stay for long periods under the Sun. If you can
stay in shade while keeping the Moon in clear view, so much the
better.
The sky in August will likely be filled with haze and humidity. It
takes but a tiny amount of either to obscure the Moon and Saturn
behind its whitish veil. In severe cases you may have trouble finding
the Moon,
Rain is unlikely early in the afternoon. A thunderstorm usually
comes in late afternoon. Just in case, be prepared to pack up and run
for shelter.
Having these warnings for a general august in the City, I note
that in 2014 summer has been more gentle to us than normal. We already
had in June and July many clear dry skies with cool breezes. Excellent
nighttime observing was accomplished, including a couple close calls
for seeing the Milky Way.
Such nights, with adjacent days, are not reliably predicted. You
could luck out!
Rarity of occultations
--------------------
Planet occultations aren't rare but for a given planet they can
occur at long intervals apart. If you're content to view an event for
ANY of the classical planets, you get the chance every few years. Here
I skip discussion of the modern planets of Uranus, Neptune, Pluto, and
the other thingies in the Kuiper Belt. These are hard to observe
against the bright limb of the Moon.
The table here gives the planet occultations visible from New York
from 2000 thru 2020. Visible means only by geometry. FOr most of the
past events, The computation came from Dance of the Planets.
---------------------------------------
LUNAR OCCULTATIONS OF PLANETS, 200-2020
---------------------------------------
UT date & hour %SL Object Magn EST SAl PA Sep
----------------- --- ------- ---- ----- --- -- ---
17/07/2001 17:28 12- Venus -4.1 14:03 58 24 7*
15/08/2001 19:40 15- Jupiter -2.0 16:00 32 2 16*
10/09/2001 12:47 52- Saturn -0.0 08:55 37 43 7*
01/12/2001 01:58 100- Saturn -0.5 20:13 -42 39 6*
28/12/2001 07:52 95+ Saturn -0.4 04:19 -33 10 12*
------------------------------------------------------
21/02/2002 00:20 56+ Saturn -0.0 20:04 -29 60 6*
------------------------------------------------------
14/10/2004 14:20 0+ Mercury -1.0 07:35 15 10 9*
09/11/2004 16:32 11- Jupiter -1.7 11:42 32 35 7*
07/12/2004 10:56 27- Jupiter -1.8 04:28 -29 27 2*
------------------------------------------------------
18/06/2007 15:09 14+ Venus -4.4 08:23 42 4 12*
12/08/2007 16:16 0- Mercury -1.9 10:23 57 61 3*
------------------------------------------------------
05/03/2008 19:00 4- Venus -3.9 15:42 23 0 8*
------------------------------------------------------
13/08/2012 19:48 15- Venus -4.3 16:01 32 0 10*
------------------------------------------------------
09/05/2013 13:56 0- Mars 1.3 08:08 37 40 8*
09/05/2013 19:09 0- Mercury -2.1 15:47 35 33 5*
------------------------------------------------------
31/08/2014 19:00 32+ Saturn 0.6 12:45 56 15 13*
------------------------------------------------------
07/12/2015 17:16 13- Venus -4.2 13:18 23 11 8*
------------------------------------------------------
05/01/2019 18:43 0- Saturn 0.4 14:35 17 16 8*
31/07/2019 20:41 0- Venus -3.9 16:51 25 23 4*
------------------------------------------------------
18/02/2020 13:26 23- Mars 1.2 08:21 16 26 6*
------------------------------------------------------
The UT date and hour are for the place on Earth of maximum
occultation, which sure as hell is not new York. The EST for New York
is NOT just five hours behind the UT hour because the geometry is
quite different between the City and the place of maximum occultation.
Both hours are for the mid event when the planet is deepest behind
the Moon, halfway between ingress and egress. To simulate an
occultation from this table, set your planetarium program to one hour
BEFORE the EST hour. Please remember that all hours for New York are
EST. Daylight Savings Time is neglected.
The columns are:
* UT date & hour, just explained above
* %SL, the percent of Moon lighted by Sun, + for waxing, - for
waning
* Object, the planet, of the classical ones *
* Magn, the stellar magnitude of the planet for the event. Planets
vary their magnitude by their distance and phase.
* EST, the mid event for New York in Eastern Standard Time
* SAl, the altitude of the Sun, - for below horizon. A positive
value means the event occurs in local daylight
* PA, the planet's altitude, substantially also of the Moon
* Sep, the separation of Moon and planet at deepest occultation.
Dance uses '*' as the symbol for arcminute.
Most of the events in the 2000-2020 take place in local daylight,
with positive solar altitude. I have far too scanty data for which
were actually observed. Many I can assume were killed by adverse
weather. The ones at night, negative solar altitude, were observed as
far as weather allowed.
Observing a planet in daytime is a special form of telescopy,
discussed below.
Daytime planets
-------------
Most home astronomers know about seeing Venus in daytime, if only
by anecdote. Some astronomers actually spotted her with one of several
methods, described in observing litterature. Some are explained below,
which you may try on Saturn on days off of the occultation.
A very few people have eyesight acute and sensitive enough to find
Jupiter by day.
The other planets are just too dim, even at their brightest, to
contrast well against the daylight sky to discern by bare eye. Some
readers speculate about seeing Mars, who dos attain to -3 magnitude
at a closer opposition. At that time, he is on the opposite side of
the zodiac from the Sun, ,out of the daytime sky. When moves into
the daytime sky Mars is quite faded by remoteness from Earth.
One common suggested trick to see a planet by day is to view thru
a long tube. It plain doesn't work.. The patch of sky seen thru the
tube is altogether too brilliant to let the planets shine thru. The
contrast of (planet + sky) against (planet) is orders too great and
for the eye to detect.
I actually tried this long-tube method while visiting a new
electric plant under construction. The host took my team to the brand-
new slip-formed chimney, some 150 meters tall. The base had a large
chamber for the precipitators and was empty at the time.
I looked yp, thinking maybe the sky will somehow be darker. I
didn't expect any stars simply because there could be none in the
zenith at the instant. The small disc of sky at the top of the chimney
was dazzling since we were getting dark adapted in the chamber.
Telescope focus
-------------
The telescope, or binoculars, MUST be accurately focused! Even a
tiny defocus, which you probably don't mind for night viewing, can
diffuse the planet into the day sky and hide it. Use the Moon, , a
distant landscape fixture,. You may focus on a star at night and then
leave the scope undisturbed until the planet 's daytime viewing.
Yet an other focus trick is to inspect the Sun with a proper front
end solar filter. Focus on the texture and structure on the solar
disc. Move the scope well away from the Sun and remove the filter,
being careful to avoid disturbing the focus.
Lunar conjunction
---------------
To spot a daytime planet you must first look toward it. Casually
scanning the sky will not work, trust me. One method of knowing where
to look is to wait until the Moon conjuncts the planet. From a
planetarium computer program or other wise, note the direction and
distance of the planet from the Moon. If your program shows daylight,
turn it off.
The Moon, so long as she is more than 20ish degrees away from the
Sun, should be found easily. The sky better be both clear and dry,
else the planet may be veiled from view. From the Moon, pace of the
distance and direction to the planet and relax the eyes. You may be
rewarded with the sight of a shiny speck. This is the planet. Use
binoculars to confirm it.
This method is available once per month, each time the Moon passes
by the planet. If the planet is in retrograde movement you could get
two hits in the month.
You could be killed by adverse weather or earthly reason that
keeps you away from the sky. On the next or previous day the Moon is
too far from the planet to guide you to it.
Surrogate star
------------
Pick a star or asterism at night having the same declination as
the planet, taken from your planetarium software. Qt night find the
star and line it up with a known landscape fixture. This can be a roof
corner, a certain tree top, telephone pole. Also note exactly where
you're standing for the lineup.
From the software diurnally rotate the sky to put the planet by
day at the same lineup place in the sky. Note the hour this occurs at.
Go out at the daytime hour , stand at your lineup spot, and look
at the lineup fixture. The planet should be near where you saw the
surrogate star at night.
Meridian transit
--------------
From your planetarium software find when and at what altitude the
planet by day crosses your meridian. This is the north-zenith-south
line in your landscape, which you probably know from your regular
nighttime observing.
About 15 minutes before the transit hour, stand in shade, to avoid
sunlight in your eyes. Scan the meridian at the planet's altitude.
Coordinate offset
---------------
This method requires that a traditional equatorial mot be properly
aligned with the celestial sphere, From your planetarium software take
the RA & De of both Sun and planet. Subtract the Sun's coordinates
from the planet's. Mind any rollover thru 0h or 0d. The results are
offsets from Sun to planet.
Some softwares can give the distance between two points in
coordinate difference as well as the straight-line angle. If so, use
these as the offset from Sun to planet.
With a solar filter attached, center the scope an the Sun .
Read the setting circles. The DE circle should be close to the actual
declination of the Sun but the RA circle, depending on the mount
design, could be all wrong. Leave it be for now.
Move the scope gently from Sun to the planet by the amount of the
offsets. Be sure to mind N-S and E-W directions.
Lock the scope and remove the solar filter..
Remove the solar filter. The planet should be somewhere in the
field of view..
Gp-to scope
---------
Finding a planet by day is one good application for a go-to
telescope. Align the scope to scope to the celestial sphere but you
will likely not see the alignment stars in the eyepiece. Assume you
did every thing correctly and tell the scope the stars are in the
eyepiece.
Pick the planet from the control console and let the scope slew to
the planet. The planet should be in the eyepiece.
If the planet is to close to the Sun, according to the limits
built into the scope, the scope may refuse to aim at the planet. Wait
for a day when the planet is receded farther from the Sun.
The planet should be in the field of view.
Planet detail
-----------
When acquired in the telescope the planet by day looks radicly
different from your usual nighttime scene. There is no glare or
halation of light from hard contrast of bright disc on black filed.
Viewing is more comfortable from the ambient daylight to
illuminate your scope, accessories, surrounds. Tools, book, printouts,
&c are in easily sight and reach
The planet's disc can show its texture far more vividly than by
night. Jupiter's belts seem more colorful because you're viewing them
with day vision over the whole field. No, you will not see any of the
moons. They are well beyond visibility by day.
Same with Saturn, where you may see that the rings are more blue
than the ball. His clods, much weaker than Jupiter's, show up more
clearly. No moons, they being way too dim for daytime viewing.
Venus could exhibit shading here and there, lost in the night view.
Mercury has no structure anyway but with him in high sky in day he's
shining thru thinner air and yields a steadier image.
Mars probably will not offer more detail than by night because he
is a pinkish hue set against the blue sky. This combination lays
tricks with most people's eyes to smooth out the disc. On the other
hand you may discern his phase as a defect from fully round.
Filters
-----
The blue sky can be darkened around the planet with a minus-blue
filter in the eyepiece. Some observers prefer a green or red filter.
You may have a set of planet-observing filters in your kit that offers
s these colors..
You can get from a e photography or typography shop a set of
tricolor filters for the primary and secondary colors. These are red-
green-blue and yellow-cyan-magenta. Look for small-diameter ones to
fit inside the eyepiece, even if you must use masking tape.
Double occultations
-----------------
The Moon occults one planet at a time, even when the planets are
close together in the sky. There's no reason why the Moon can not
cover two planets in close proximity but as far as I know this was
observed ONLY ONCE in human history.
On 1998 April 23 Jupiter and Venus were in close conjunction AND
the Moon covered BOTH of them! This occurred in New York when the Moon
was sown. New York saw The Moon rise AFTER she passed the planets. .
Observers fanned out in mid and south Africa and Atlantic Ocean to
watch it. The planets immerged and emerged within a couple minutes of
each other!! I haven't yet heard of any predictions for the next
possible instance of a double planet occultation.
Conclusion
--------
Occultations of planets by the Moon are beautiful events. Even
those by daytime, provided weather and skill are on your side. Else
you will bomb out. It really pays to practice seeing Saturn in the
clear days before the occultation. The effort will prepare you for the
big day.
This August 31st Saturn occultation is one of the better ones
geometricly but it occurs when weather is likely to be hazy and humid.
It could also be cloudy or rainy. New York in the 2013-2014 period so
far lost many fantastic eclipses and occultations due to weather. This
is the grandest unpredictable factor of all observing programs.