GRAPHICAL METHOD for DETERMINING HELIOGRAPHIC COORDINATES of SUNSPOTS

   

HELIOGRAPHIC COORDINATES of SUNSPOTS

   Described here is a graphical method for determining the
heliographic coordinates of sunspots utilizing white light
projection of the solar disk onto a Stonyhurst disk.  Such
projection is imaged with a Logitech QuickCam Pro which is mounted
inside the projection tube.  The Samouce Solar Facility, 6" f/10
refractor in "Projection Mode" is utilized for generating this
image.  The attached jpg file is made available to the SolNet
community through the Rik Hill site
www.lpl.arizona.edu/~rhill/alpo/solstuff/recobs.html and may be
freely distributed.

The Instrument (projection mode):
     Location: Bitterroot Valley, Sula, Montana, USA (40 deg 15 min
N, 114 deg 09 min W, alt 4220')
     Optics: Jaegers 6", f/10 achromatic objective w/Optica b/c 50mm
Huygenian projection eyepiece
     Mount: Parallax Instruments 125 German Equatorial w/Losmandy
482 digital drive
     Camera: Logitech QuickCam Pro w/Optica b/c 1.0 ND filter (1%
transmission)
     Computer: CTX EzBook, Win 98
     Software: Logitech QuickCam PRO, v  4.1.1, Diffraction Limited
MaxIm DL, v 1.61

Method:
     1)  Heliographic data for the day is selected ( resource 3).
     2)  Appropriate Stonyhurst disk (nearest degree, resource 2) is
selected and mounted to the projection screen with the top oriented
to solar north and solar east to the right.
     3)  The x-axis is oriented parallel to the Earth's equator as
projected onto the sun by allowing a prominent sunspot to drift
across the Stonyhurst disk East-West axis with the drive turned off.

     4)  The Stonyhurst disk is oriented to the heliographic
coordinates by  rotating to the Position Angle, P (+ rotate CW, -
rotate CCW) to align the y-axis to the sun's axis of rotation
(resource 4).  The solar disk is centered on the Stonyhurst disk.
Then the exposure taken (see A]  Quick Cam Pro Settings:).
     5)  The image is saved as a jpg file having the following
convention: YYMMDDhhmm for year (YY), month (MM), day (DD), hour and
minute UT (hhmm).
     6)  The image is further processed by MaxIm DL (see B]  MaxIm
DL Settings:).
     7)  The resulting sunspot image has rather poor definition with
only prominent spots being seen.  Their heliographic coordinates can
be determined by comparing the spot relative to Lo and Bo (see
resource 1, "Sunspot Location", "Graphical Method") and matched to
higher resolution images (resources 5, 6 & 7).

Resources:
     1)  Solar Observing by Peter Meadows
(http://www.meadows3.demon.co.uk)
     2)  Stonyhurst Disks
(http://www.meadows3.demon.co.uk/stonyhurst.html)
     3)  Heliographic Data
(http://www.meadows3.demon.co.uk/hellocoords2000.txt)
     4)  The 150-Foot Solar Tower Sunspot Drawing
(http://www.astro.ucla.edu/~obs/150_draw.html)
     5)  White Light Image from BBSO
(http://www.bbso.njit.edu/Images/daily/images/wfullb.jpg)
     6)  Intensitygram Image from NSO
(http://www.nso.noao.edu/synoptic/pi2.gif)
     7)  MDI Continuum Images from SOHO

A]  QuickCam Pro Settings:
          Lightning tab:
              Brightness =180
              Contrast = 225
              Automatic Brightness = off
              Cyan/Red Value = na
              Yellow/Blue Value = na
              Saturation Level = 0
              Automatic Color = off
              Advanced... button:
                  Exposure Time = 68
                  Compression Level = 0
                  Light Sensitivity = 255
                  Low Light Filter = off
         Format tab:
              Large Size 640 x 480
              Number of Colors = Millions (24-bit)
              Mirror = off, Rotate = off, PictureSmart = off

     B]    MaxIm DL Settings: (default except)
                 Process - Stretch:
                     Permanent Stretch Type: Gamma = 0.8
                     Input Range: Screen Stretch
                     Output Range: 16-bit (0-64K)

        JWS