Predicted profile for a 3.9-mag. graze of gamma Librae across Penn. and N.J. Sat. morning promises huge numbers of events

New February 16, 2017, 8pm EST

 
Tomorrow night, actually early Saturday morning, Feb. 18, there will be 
a lunar grazing occultation of 3.9-mag. gamma Librae = ZC 2223 (sometimes 
known as Zuben-el-Akrab) (spectral type K0III) visible along a path near 
the southern limit of the occultation that extends from southern 
Manitoba (near Moonrise), across n. Minn., n. Michigan, s. Ontario, 
n. Lake Erie, the southwestern corner of New York, n. central and s.e. Penn.,
and central New Jersey.  For information about this whole path, click here.
It gives the Universal Time of central graze (8:12 UT = 2:12am CST in 
Manitoba to 8:33 UT = 3:33AM EST in New Jersey, where the altitude 
will be 28 deg. above the southeastern horizon) and circumstances at 
half-deg. intervals of longitude.  The graze will occur in a low part 
of the Moon.  An interactive Google map of the whole path is here.
If you put -3.5 and -2.0 in the boxes above the map and click to 
accept these graze offsets, you will get the approximate wide graze 
zone, defined by two dark gray lines, that you can zooom in on in 
different parts of the path; note that no occultation will occur at 
the green line marking the spherical-Moon southern limit, due to the 
low lunar topography.  The star may be a close double, based on 
previous occultation reports, adding interest to the event.  The 
graze will occur 9 deg. from the south cusp of the 54% sunlit waning 
Moon. The star will appear to approach the Moon from the bright side, 
passing over the southern cusp about 7 minutes before central graze.

The lunar profile lines up especially well in a narrow (about 150-meters 
wide) strip extending from north-central Penn. to central N.J., 
so that area is what I concentrate on in the discussion below.
We only get chances for lots of multiple events like this with a 
star so bright under good graze conditions, within 150 miles, 
only once every two or three years.
The path is shown by the dark gray line on this map of e. PA & NJ.
The following Google Map files can be used to cover areas with 
different heights above sea level; select one that is within 120 ft. 
of the elevation of the area from which you plan to observe. For all,
use offsets of -3.05 and -2.90, that defines the 150-meter-wide 
best multiple events zone shown on the predicted profile.

 40 feet
150 feet
 400 feet
 465 feet
 610 feet
 770 feet

The narrow path is shown a little better between the two dark gray 
lines on this map of the northwest Philadelphia suburbs (from 
Kutztown to Lansdale) and on this one over northern Philadelphia 
and west-central New Jersey (Prospectville, PA to Buddtown, NJ).

I have used the Google Maps to generate very detailed static maps of the 
narrow path (between the two dark gray lines) for several potential sites 
that might be used, in general, public parking lots or small roads at parks, 
schools, businesses, and churches.  Listed from west to east (opening the maps 
give approximate longitude and latitude at the bottom; use that with the 
detailed path information to find the Univ. Time for the site of interest):

Jersey Shore, PA Route 44, elev. 615 ft.
Antes Fort, PA Village Park, elev. 615 ft.
Milton, PA e. of Cherry St., elev. 464 ft.
Northumberland, PA s. side US 11, elev. 465 ft.
Elysburg, PA parking lots s.e. of E. Valley Ave., elev. 610 ft.
Mt. Laffee Rd., PA s. side, over coal strip mine, elev. 770 ft.
s. Kutztown, PA St. Mary's Catholic Church, elev. 400 ft.
n.e. Philadelphia, PA Flyers Skate Zone, Decatur Rd., elev. 100 ft.
Willingboro, NJ Memorial Jr. High School, elev. 32 ft.
Willingboro, NJ Indel Ave. commercial rd., need permission, elev. 60 ft.
Mt. Holly, NJ Holly Hills Elementary School, elev. 35 ft.
Mt. Holly, NJ Iron Works Park, elev. 12 ft.

The preferred site is the parking lot of St. Mary's Catholic Church 
on the south side of Kutztown, PA.  The longitude there is -75.805, so 
central graze will occur there at 8:30:33 UT = 3:30:33am EST; the profile 
shows that the graze events will occur from -1.2 min. to +1.8 min relative 
to central graze, or for that location, from about 8:29:15 to 8:32:20 U.T.
The Canadian weather forecast for 
astronomy now shows (Thurs. afternoon) that it will be clear across Penn. 
and NJ for this graze, but other forecasts aren't as optimistic.  The 
Skippy Sky forecast shows clouds decreasing across Penn. from n.w. to 
s.e., and likely clear over N.J. The National Weather Service shows 
fairly uniform 40% cloud across the path.  We'll see tomorrow (Friday) 
before deciding which location to select, and will post here in the
afternoon, and distribute by e-mail as well.

For the very successul graze of Aldebaran observed in Oklahoma and 
Texas on July 29th, recorded at 7 stations, 5 remote, by David and 
Joan Dunham near Carey, TX, click here.
View some of those videos to see what you might observe Sat. morning 
during the gamma Librae graze. Fresnel diffraction will cause gradual 
and partial events during the gamma Librae graze, like those you can 
see in the Aldebaran graze videos.  

Techniques for timing occultations using whatever resources that you 
may have are described here.
Much information about observing occultations of all types is in 
"Chasing the Shadow:  The IOTA Occultation Observer's Manual" 
available for free download here.
_____________________________

David Dunham, 2017 February 16
e-mail:  davidwdunham@verizon.net (and temp. dunham@starpower.net).
cell phone:  301-526-5590