John Pazmino
 NYSkies Astronomy Inc
 2013 May 3
    The NYSkies territory is treated to a rare double occultation of a 
star AND a graze covering of either or both of them! On the evening of 
Friday 24 May 2013 beta Scorpii, Graffias, is covered by the nearly 
full Moon standing low in southeast. The extreme edge of the Moon's 
shadow cast by the star sweeps over New York City.
    The star has two members, beta1 the brighter and southern of the 
two, and beta2, the dimmer and northern one. Each throws its own 
shadow of the Moon onto Earth, which overlap by about 41 kilometers. 
New York City sits in the overlap zone! 
    There are a variety of amazing scenes no matter where you observe 
from. From north to south across the NYSkies territory the scenes are 
    * a very close miss of both stars 
    * A graze of beta1 and a miss of beta2. 
    * A total covering of beta1 and a miss of beta2
    * A total covering of beta1 and a graze of beta2
    * A covering of both stars 
    The City, except in its south parts sees the total & miss scene. 
The south parts in Brooklyn and the Rockaways sees the total ^ graze. 
Staten Island get the brief total & total.  
    Each scene is spectacular, removing the compulsion to travel away 
from home. Where ever you are in NYSkies land, you get a grand show.  
On the other hand, the dense transit network our our region does allow 
convenient easy travel to a more favorable observing site. 
    This event requires a telescope to bring out Graffias against the 
brilliant edge of the full Moon. Bare-eye and binoculars are not up to 
this task. The scope may be of modest size, such as a totable model. 
    The NYSkies Astronomy Seminar of Friday 17 May 2013 will prepare 
observer's for this event, with takeaways charts and tables. 
    Occultations are routinely calculated and published with Universal 
Time, or similar prime time standard in Greenwich, UK. In this time 
the occultation occurs on May 25th. Please be wisely about timezone 
shift! Universal Time is four hours AHEAD of Eastern Daylight Savings 
Time. In New York, and thruout North America, the calendar date is 
Friday 24 May 2013. 
    If you go out on Saturday the 25th, misreading the published 
information, you'll be surprised and infuriated to see the Moon some 
13 degrees east of beta Scorpii! 
    This star has several names. I use Graffias (GRA-fee-yass) here. 
An other common name is Elakrab (ell-a-KRABB), with variant spelling. 
Star names are not official and you may use which ever of them you 
like or make up your own. 
    It is the northern of the three main stars in the asterism Caput 
Scorpii. The other two in this group are delta (Dschubba) and pi. With 
several fainter stars in Caput this is a pretty field for binocular 
exploration when the Moon is away. 
    Graffias was discovered as duplex by Castelli in 1627. Castelli is 
a little-appreciated astronomer, commonly missed in astronomy history. 
He was a colleague of Galileo who called his attention to several new 
features in the sky. One was the prospect of using the newly found 
double stars, Mizar is particular, to determine stellar parallax. 
Such a measurement would prove the motion of the Earth around the Sun, 
favoring the Copernicus model of the solar system. Beyond astronomy 
Castelli is the founder of modern hydrology, and his work is still 
valid today in engineering of water projects. 
    Graffias has the Bayer name beta Scorpii and Flansteed name 8 
Scorpii. After we recognized the twin nature of Graffias we applied 
beta1 and beta2 to its components. Flamsteed 8 applies to the stars as 
a unit because apparently Flamsteed didn't resolve it with his simple 
weak telescope. 
    Some facts & figures about the stars are listed here
    property    | beta1           | beta2   
    Bayer name  | beta1 Scorpii   | beta2 Scorpii 
    Flamsteed   | 8 Scorpii       | same, not resolved 
    Bright Star | HR 5984         | HR 5985 
    Smithsonian | SAO 159682      | SAO 159683 
    Tycho       | TYC 6208-1623-1 | TYC 6208-1622-1 
    Pos Pro Mot | PPM 231174      | PPM 231175 
    Zodiacal    | AC 2302         | none 
    H Draper    | HD 144217       | HD 144218 
    DD number   | BD-19:4307      | BD-19:4308 
    CPD number  | CPD-19:05945    | none 
    Visual magn | +2.62           | +4.84 
    Distance    | 400 lightyears  | same 
    Radial vel  | -1.0 km/s       | same 
    Spectrum    | B1 V            | B2 V 
    RA (2000)   | 16h 05m 26.235s | 16h 05m 26.564s 
    Dec (2000)  | -19d 48m 19.63s | -19d 48m 06.84s 
    B-V index   | -0.072          | -0.034 
    There are several other companions in the beta Scorpii system. 
Probably none are visible for this occultation. Beta2 is in double 
star work 'beta C' because beta1 has an other close companion 'B'. 
    The distance to the system is now usually cited as 400 lightyear 
from analysis of HIPPARCOS data. Works before HIPPARCOS, thru the late 
1990s, give various distances up to 800 lightyears. 
Shadow path
    The Moon's shadow is a cylinder formed by the parallel rays of 
light from the star at indefinite distance away. On the ground the 
shadow is a disc, distorted by the Earth's curved surface, of the same 
diameter as the very Moon, about 3,500 kilometer. Standing inside the 
zone sweeped over by this shadow you see a total occultation of a star 
the Moon passes in front of. 
    By standing at the north or south limit of the swath you see the 
star nicked by the lunar limb. The star blinks in and out between 
lunar mountains sliding across it. This is a graze occultation. 
    For the 24 May 2013 occultation, beta Scorpii is grazed by the 
northern limb of the Moon. Because the star is a double star there are 
TWO lunar shadows, one for each star. They overlap with TWO parallel 
north edges 41 kilometers apart. You see a graze of the one or the 
other star, according as the edge line you stand on. 
    The Moon's shadows enters the NYSkies region from the west-
northwest, races east and southeast directly over the City, crosses 
Long Island, and leaves NYSkies over Atlantic Ocean in the east-
southeast. The passage takes only a couple minutes, given that the 
Moon's shadow speed on the ground is some full kilometer per second. 
    The limit lines pass over or near numerous major towns. Select 
ones are listed here in alphabet order to generally delineate the 
limit lines. 
    Deer Pk LI, Glen Cove LI, Greenwood Lk NJ, Islip LI, Mamaroneck 
NY, Mahwah NJ, Melville LI, New Rochelle NY, Pearl Rv NY, Ramapo NJ, 
Ramsey NJ, Ringwood NJ, Spring Vy NY, Suffern NY, Syosset LI, West 
Babylon LI, West Milford NJ, Yonkers NY 
     Andover Twp NJ, Bayonne NJ, Bensonhurst BK, Canarsie BK, Denville 
NJ, Dover NJ, East Orange NJ, Elizabeth NJ, Green Twp NJ, Hanover NJ, 
Hopatcong NJ, Livingston NJ, Manhattan Bh BK, Mill Basin BK, Morristown 
NJ, Newark NJ, Parsippany-Troy NJ, Randolf NJ, Rockaway Pk QN, Roxbury 
Twp NJ, 
    In addition to towns the paths cross many parks, reservations, 
beaches. These may be open for public use for the occultation. 
    These lines are for a smooth lunar globe that skirts the TOPS of 
mountains expected to stand along the limb for this occultation.
    It may be that a site a kilometer or two SOUTH of the limit line 
will capture many blinks of the corresponding star between the 
mountains and thru the valleys. Farther south of the limit than 3 or 4 
kilometers yields a total, very brief, occultation of that star. 
    You really need a telescope, even a tabletop or totable model. By 
eye the Moon's brilliance makes you lose Graffias long before it is 
hit by the Moon and next catch sight of it well after the Moon left 
it. Binoculars are a poor substitute because still the glare of the 
Moon may overpower the star. 
    The telescope should have an aperture of at least 120mm to see 
Graffias comfortably against the lunar disc. If your eyesight be extra 
acute a smaller aperture, down to 90mm, may be used. There is no need 
for a overly large scope being that there is no detail to be seen on 
the Moon or the star that calls for huge aperture or magnification. 
    A clockdrive avoids the distraction of manually nudging the scope 
to follow the star's diurnal motion. Either a conventional equatorial 
drive or a stepwise altazimuth drive is good. The latter is what a go-
to scope uses when in altazimuth mode with its base sitting on a solid 
level table. . 
    Tracking on the stars lets the Moon float across the field of 
view. Tracking on the Moon lets the stars glide behind the Moon. Which 
to use is by your preference, 
    For a go-to scope be SURE to properly home and align it well 
before the occultation. Even with the bright Moon there are enough 
target stars to choose from. Some go-to scopes offer a planet based on 
its onboard ephemeris. Do NOT use Saturn! Stay with fixed stars. 
    The expected warm weather in late May relieves you of the concern 
about cold-failure of batteries and electronics. On the other hand, 
May nights can be humid, giving worry about moisture problems. 
Directions in the scope
    The event occurs at the north limb of the Moon. The Moon glides 
eastward over the star. The sky's diurnal rotation is toward the west. 
Beta2, the dimmer star, is almost straight north of brighter beta1. 
    If you be new to lunar observing, please practice exploring the 
Moon in your scope one days before the occultation. This will firmly 
familiarize yourself with the lunar topography and keep your sense of 
directions right way round. 
    Be mindful of mirrored imaging from the peculiar optics of your 
telescope! It may be helpful to make a mirrored moonmap to be sure you 
can identify features along the lunar edge. Many lunar observing 
computer programs have this feature, else do the flip in an image 
Moon's glare
    To temper the glare of moonlight, use as high a power as practical 
to dilute the lunar disc and still have a firm optical image of the 
stars. The amount of magnification is largely governed by the quality 
of the air and of the instrument. Too high a power may make tracking 
the stars too tedious, even with a well-regulated mount. 
    For catching the blinks of the star at a site on one of the limit 
lines, use the highest possible magnification that your scope, eyes, 
and sky can accept. Too low a power may miss the lash of the star next 
to a bright mountain side. 
    One worry is a hazy night where the Moon is a diffuse or frosted 
disc. The sky around her may be so lighted that Graffias is veiled out 
of sight. As long as the lunar disc shows its features distinctly you 
should have a good view of the occultation. 
Observing sites 
    This event does not require travel away from New York City. The 
view from any where in the City, even from Manhattan, is spectacular! 
You need a clear view of the low southeast and south sky. You must see 
the Moon! Scout out a nearby park or waterfront or roof if you can not 
observe from your home. 
    Do not view thru closed windows for the distortion they cause in 
the telescope image. Many office towers have tinted windows that may 
not be obvious in bright sunlight. They will dim the stars to vanish. 
    If you have friends or family near either graze line, go and ask 
for a visit to show them the occultation. 
    The NYSkies area has a dense transit network with stations at 
towns all along the graze lines. Take a bus or train into the graze 
zone. You may view from the transit station or adjacent field. Only 
totable equipment is allowed on transit vehicles. 
    Service on Friday nights on almost all routes is at least hourly 
in both directions, allowing for a comfortable trip with moderate 
deadtime. You still have to keep in hand a current timetable. Off-peak 
fares should be in force after about 20h EDST. 
    A reverse ride may be the trick for observers in the Catskills, 
Hudson Valley, mid to north Westchester, Connecticut, mid to east Long 
    To use a park or other public land you do need your own wheels. 
Transit gets you to the main gate or a nearby busy street, but not to 
any interior section. You either have a long walk to drag your gear or 
make do with viewing from the gate or street. 
Public viewing 
    Several astronomy centers have regularly scheduled starviewing 
sessions on Friday the 24th and will for sure feature this occultation 
for their visitors. Special sessions for the show may be arranged. As 
NYSkies learns of them they are posted into the NYSkies yahoogroup. 
    Because the stars blink in and out of view in an instant, only 
fleeting views can be offered per instrument. With many telescopes and 
a smaller audience, this can be worked out. 
    With modern digital imaging equipment is to present live 
projection of the occultation for a larger audience to enjoy. Lacking 
live imaging, the starwatch may have a computer running a planetarium 
program. The simulated scene of the Moon crossing beta Scorpii runs in 
real time to match the sky outside. This is handy for intermittent 
clouds. If the planetarium shows beta1 and beta2 separately, the 
simulation is much more realistic. 
    There is no special preparation to attend an occultation session. 
What's needed for any other mid spring night starviewing is all you 
need. You may want to have your camera to hand to take a shot of a a 
projection screen or thru a telescope eyepiece. 
    Depending on your location you get one of several amazing views: 
    location                  | beta1 | beta2 
    north of north limit line | miss  | miss 
    on north limit line       | graze | miss 
    between limit lines       | total | miss 
    on south limit line       | total | graze 
    south of south limit line | total | total 
    The duration of the occultation increase with locations farther 
south of the southern limit line. 
    Because beta Scorpii is a wide double star, some calculations are 
issued for each star, with TWO limit paths. The NORTHERN one is the 
graze limit for beta1, the SOUTH component of the pair. The SOUTHERN 
line is for beta2, the NORTH member. Most computations so far seem to 
apply only to beta1, the southern and brighter star. 
    When calcs are issued for 'beta Sscopii' as a single star, they 
are for beta1. The limit line is the one passing north of New York 
City, thru Westchester county. There is no southern line foe beta2. 
    One curious factoid is that with the angular diameter of beta 
Scorpii (either star), its disc projected on the ground in the City's 
reach of the graze line, is TWO to THREE meters in diameter! A person 
three meters away may see one set of blinkings during the graze while 
you see a different series. 
Manhattan view
    You must have a clear view of the low southeast and south sky. You 
may have to seek out a site, like a riverfront park, for this event. 
Mind well that directions in all occultation, and other astronomy, 
litterature are geographic, NOT along Manhattan's street grid. 
'Downtown' within the grid is toward azimuth about 210 degrees, more 
southwest than straight south. 
    For Manhattan here is the timetable of activity on the evening of 
2013 May 24 Friday: 
    EDST  | event             | Sun    | Moon   | remarks 
    19:53 | moonrise          | 02 296 | 00 116 | 99% 178E L-1.7 B-1.2 
    20:13 | sunset            | 00 298 | 04 119 | Moon not quite full 
    20:46 | civil twilight    | -- --- | 08 124 | end of daylight 
    21:27 | nautical twilight | -- --- | 13 132 | full night in NYC  
    22:05 | beta1 ingress     | -- --- | 18 139 | pos 22d, ver 54d 
    22:11 | mid occultation   | -- --- | 19 141 | beta2 close miss 
    22:16 | beta1 egress      | -- --- | 19 142 | pos 34d, ver 352d 
    00:55 | moon on meridian  | -- --- | 29 180 | on May 25th 
    Times in this table may differ from other sources due to assumed 
geographic location of 'Manhattan' or 'New York'. You would be on duty 
many minutes before the ingress to follow the stars into the Moon and 
then watch for their emersion some 11 minutes later. 
    Sun and Moon columns give the altitude and azimuth of these bodies 
for the associated event. 
    For moonrise the percent of lunar disc lighted by the Sun, Moon 
elongation from the Sun, and libration are given. These are fixed for 
the whole duration of the occultation. 
    The libration, L for longitude, B for latitude, are the lon-lat on 
the lunar surface for the apparent center of the lunar disc. That's a 
real minus signum, not a hyphen, in the figures. They, combined with 
external maps and tables, approximate the profile of the mountains and 
valleys near the ingress and egress points. 
    For the ingress and egress the pos and ver angles are given. Pos 
is the position angle along the lunar limb measured anticlockwise from 
celestial north. This is useful for scopes on an equatorial mount. 
    Ver is the vertex angle along the lunar limb from the vertex or 
top of the Moon, also anticlockwise. This is for an altazimuth 
    There is in the usual ephemeris of occultations a cusp angle, the 
angle along the lunar limb from one or the other cusp. With the Moon 
almost full there are no obvious cusps. This angle is omitted here. 
Other occultations
    Graffias is one degree north of the ecliptic. The Moon can occult 
it only when her ascending, like for this instance, or descending node 
are nearby. Because the nodes migrate westward in the ecliptic about 
19 degrees per year, there can be only a few hits on Graffias before 
the node carries the Moon too far away to touch the star. There is 
then a long span of misses. The occultation season of Graffias is only 
1-1/2 years at each node with an 8 years gap in between. The nodes 
alternate in generating occultations, completing a full cycle in about 
19 years. 
    Of all the occultations possible, only some are over the City. The 
rest are in other parts of the world. I did not recall the last 
Graffias event. I checked and found that there is a good reason why I 
didn't recall any. 
    As far back as the mid 1980s there was ONE occurrence for New 
York. It was on 9 January 2002 in daylight with no hope of seeing it 
with visual means. 
    For the future into the mid 2030s there is only ONE hit for the 
City, 18 July 2013. It takes place in daylight, being unobservable by 
ordinary visual methods. 
    As fate falls to us, this one on May 24th is the LAST CHANCE to 
see Graffias covered by the Moon from New York, specially if you're on 
Social Security. 
Hierarchy of orbits 
    Beta Scorpii is a wonderful example of the hierarchy of orbits in 
double star systems. In the solar system or planetary systems at other 
stars, the orbits of the planets can be more or less arbitrarily 
arrayed around the central star. The orbiting bodies are of minuscule 
mass compared to the central star and their orbits are governed almost 
entirely by that star's mass.  
    In a stellar system the orbiting bodies are of similar mass, a few 
solar masses each. Their orbits end up nested in a hierarchy where 
each level is many times larger than the next inner one. Graffias is 
one such system, whose information was sussed out partly be watching 
its components during lunar occultations. 
    The diagram here shows the beta Scorpii orbit levels with the 
orbital periods for each component. The letter designations are a bit 
inconsistent in double star work but context clarifies the identities. 
        A (beta1) 
        |       |                              | 
        D       B                              C (beta2) 16,000yr 
        6.82dy  610yr                          | 
                                               E 39yr 
                                               F 10.7dy 
    Beta1, A, has three companions, B and C and D. C has one companion 
E, which in turn has its own companion F. The system, so far, has six 
components. Of them, A and C are the obvious pair in small scopes. B 
is discernible in large scopes by keen observers. 
Other nearby targets 
    After the Graffias show you may want to explore the region around 
this star. Because of the full Moon, probably all clusters and 
galaxies are washed out, even in a clear dark sky. To fill your 
observing needs, here are several double stars, targets well suited 
for a bright sky condition, within about 20 degrees  west, north, and 
east of beta Scorpii. All of these stars are within range of small 
scopes from New York City. 
 cns designatn RA2000   DC2000 MagA MagB sep   colors  year
 --- --------- -------- ------ ---- ---- ----- ------- ----
 Lib mu        14 49.3  -14 09 5.8  6.7    1.9 whi     2003 
 Lib alp1-alp2 14 50.9  -16 02 2.8  5.2  231   whi y-w 2002 
 Lib  33       14 57.5  -21 25 5.9  8.2   25   ora red 2002 
 Sco   2       15 53.6  -25 20 4.7  7.4    2.1 b-w whi 1991
 Sco xi        16 04.4  -11 22 4.9  7.3    7.5 yel     2005 
 Sco bet1-bet2 16 05.4  -19 48 2.6  4.9   13   b-w b-w 2005 
 Sco nu1-nu2AC 16 12.0  -19 28 4.3  5.3   41   b-w     2005 
 Sco nu1    AC 16 12.0  -19 28 4.3  6.4    1.3 b-w     2003 
 Sco  12       16 12.3  -28 25 5.9  7.9    3.8 b-w     1999 
 Sco sigma     16 21.2  -25 36 2.9  8.5   20   b-w     1999 
 Sco alpha     16 29.4  -26 26 1.2  5.4    2.7 red b-w 2000 
 Ser   6       15 21.0  +00 43 5.5  8.8    3.0 ora     2000 
 Ser delta     15 34.8  +10 32 4.2  5.2    4.0 y-w y-w 2009 
 Ser nu        17 20.8  -12 51 4.3  8.3   46   whi 
    The colors are the schematic ones for the spectra of the stars. 
They are NOT the colors you will -- or should! -- discern ub the 
doubles. Some observers claim that when seen in a gray sky, in this 
case lighted by the Moon, the colors of double stars are easier to 
appreciate. Your experience may vary. 
    The year is the year for the separation, being that double stars 
carry out orbital rotation over the decades.
    Rho Ophiuchi is a multiple star. You may spot one or two other 
comites next to it. Alpha Scorpii (Antares) usually smothers its 
companion behind its own glare. Alpha Librae (Zubenelgenubi) could be 
seen as double by bare eye, else use binoculars. 
Occultation science 
    As many of us elders know, there was until this century a lively 
practice of observing occultations. We used radio time signals from 
WWV or CHU shortwave stations, a tape recorder, stopwatch to record 
the instants of ingress and egress. This helped refine the lunar 
motion and position, in part to assist in the 1960s Apollo project. 
    For a graze we watched for the multiple blinks of the star as the 
lunar mountains cut in front of it. Each on/off, in/out, see/saw was 
dutifully recorded. The sequence of the blinks mapped out the 
topography of the Moon in the north and south polar regions. 
    Lunar occultation helped to to discover and study binary stars 
that were too close to observe be ordinary optical means. The timings 
and photometry for each component of the pair, plus the geometry of 
the occultation, gave the separation and orientation of the two stars, 
even if they were not seen individually for their tight proximity. 
    In the 21st century these, and other traditional, occultation 
works rapidly became obsolete for home astronomers. While occultation 
reports are still collected, there is a much lesser need for them. New 
methods, including visits by spaceprobes and nonvisual imaging 
methods, displaced occultations in many classical applications. 
    In spite of the diminished science value of home observations, the 
sheer beauty of the event never lapsed. It is also one of the handy 
ways to appreciate within a few minutes the real orbital movement of 
the Moon. Try taking pictures of the scene. Graffias is in the head of 
Scorpius, with the body and heart beneath it around Antares. Use the 
techniques for skyscape pictures. 
    Occultations of bright stars are common with several occurring 
over New York each year. They are fun to watch and are a vivid 
demonstration of the Moon's real orbital motion thru the zodiac. 
    Occultations of bright double stars are rarer for the small number 
along the zodiac. Usually the two stars are so close together they 
blink out behind the Moon within a split second apart. You see a step 
decrease in brightness, then the full cutoff of light. At egress first 
a dimmer star is seen, then it snaps into full brightness. 
    Occultations of wide doubles, with well-spaced components, are 
rarer with only a couple possible targets in the Moon's corridor. You 
see a double ingress and double egress. 
    Occultations over the City near the shadow edge, creating a graze 
event, are common. Almost all are of dim stars with little motive to 
make the trip to the limit line. 
    This one shot instance for beta Scorpii, a bright star, a wide 
double, and a graze near the City, is an event you better make effort 
to watch! If you are confined to your home, you get one of the five 
stunning scenarios explained above. By taking a short ride you get any 
other one of the scenarios. 
    Like for all celestial observing, clouds can wipe out your view. 
Even a thick haze or thin cloud can kill the show. On the other hand 
you don't need a perfect or extra good sky.