John W. Samouce
(copyright 1999)

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 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 ( 2) Stonyhurst Disks ( 3) Heliographic Data ( 4) The 150-Foot Solar Tower Sunspot Drawing ( 5) White Light Image from BBSO ( 6) Intensitygram Image from NSO ( 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

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