The 'necklace' stars in Pleiades: comparison of Judaculla and NASA image.
There is a little string of stars in Pleiades that I think of as 'the
necklace stars' - small in binoculars but crisp and good to use for
focusing accurately. They look like small diamonds in the shape of a
necklace when Pleiades is in the western sky.
In the image above, look at the NASA photo which shows part of the
necklace stars. Now think of 'the Rock' star map not as symbolic, but
pictorial - a rock carved picture imitating what is seen.
The 'necklace' stars in Pleiades: A Hubble Space Telescope Archive footprint from STScI.
Using Space Telescope Science Institute's HST archives, I brought up a footprint of 0.5 degree
for Pleiades, M45, at the coordinates RA = 56.740000 Dec = 24.000000 r = 0.5 [03:46:57.600 +24:00:00.00].
The above image shows the line of small stars that resembles a necklace - appearing as bright jewels in small 10x25
binoculars. The Pleiades is oriented as it would appear, setting in the western sky. The blue swirls
surrounding the stars are remnants of a gas nebula. Pleiades has long been a marker for both Autumn and
Spring in several cultures.
The Mathematical Determination of Winter Solstice Sunrise at Judaculla Rock
The angle of declination of the Earth's axis is 23.44 degrees (NOAA). The Sun strikes the Earth as it orbits around the Sun, the axis declination shifting the seasons from summer to winter when the axis points toward or away from the Sun. The midpoint of this axial shift is parallel to the Sun at the Equinoxes.
A mathematical formula describes the orientation of the Earth axis and the Sun with regard to Latitude:
cos (A) = sin (declination angle)/cos (latitude)
Where 'A' represents the complete spread of rise or set points North and South of the Equinox. 'A/2' then will equal the angle either North or South of the 0 degrees at Equinox. The latitude for Judaculla Rock is 35.5 degrees (USGS).
Using a scientific calculator:
sin (declination) = sin (23.44) = 0.3977885
cos (latitude) = cos (35.5) = 0.8141155
cos (A) = sin (declination)/cos (latitude) = 0.3977885/0.8141155 = 0.4886143
'A' then = 60.75 degrees for the complete North to South rise or set points.
'A/2' = degrees South for the Winter Solstice sunrise = 30.375 degrees south of due East.
Translating this into degrees from true North, 30.375 + 90 = 120.375 degrees from true North. To find the corresponding Summer Solstice sunset, 120.375 + 180 = 300.375 degrees from true North. Magnetic North is 4.5 degrees east of true North, so to see what a magnetic compass must read, 300.375 + 4.5 = 304.875 degrees from Magnetic North. In 2009 Ray Urbaniak of Utah, while in Asheville, NC, measured the bearing of the prominent grooved line on the right side of Judaculla Rock and photographed the compass face, which read 304 degrees. He used a Sylva compass with 2 degree gradations. The mathematical calculation is less than a degree off of his compass reading.
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