SunGrid - Determining Positions on a Solar Photograph
Description
SunGrid is a MS Windows (c) based VB.NET program for digital astrophotographers who specialise in imaging the Sun. It is used to locate features on the sun, such as sunspots, faculae etc. in terms of their latitude and longitude on the sun’s surface. It is based on the idea of a Stonyhurst Disc. (How a Stonyhurst Disc is used is well described on page 69 of the book “The Sun and How to Observe It” by Jamey L. Jenkins, Springer (2009). ) Note that to measure a solar photograph, the user must be aware of the camera’s orientation when the photograph was taken. This requires the upper or lower edge of the photo frame to lie in the E-W direction. These procedures are described in the book by Jenkins.
To use SunGrid, first click on the SunGrid icon to start it up, then minimise it temporarily to stop it blocking your desktop. Next bring up a digital solar photograph on the computer screen using your favourite viewer and expand it to a convenient size. Restore the SunGrid so it now overlays the photograph. Sungrid is transparent and allows the sun’s image to be seen beneath the grid. The SunGrid window must be repositioned, by dragging the top with the cursor, and resized by “pulling” the window from any of the corners or sides in the usual way to obtain a fit of outer circle of the grid to the sun’s diameter.
If required, the transparency of the SunGrid window may be altered using the slider at the bottom of the window, and the brightness of the grid may be altered using the slider at the top of the window. You probably will not need to touch these.
To use the grid, three parameters are required:
Lo – The heliographic longitude of the centre of the Sun’s disc
Bo – The heliographic latitude of the centre of the Sun’s disc
P – The position angle of the north end of the Sun’s axis of rotation
All of these parameters can be obtained, for any particular day, from the Association of Lunar and Planetary Observers (A.P.L.O.) website at http://www.alpo-astronomy.org/solarblog/ in the section “A.P.L.O. Solar Ephemerides”.
Setting the Bo parameter on SunGrid is achieved through the slider on the left of the window. The current Bo value is shown in the SunGrid window, bottom left (see above figure). Setting the P parameter on SunGrid is achieved through the slider on the right of the window. The current P value is also shown bottom left. Now, positioning the cursor over a feature of the Sun and clicking will mark the position with a cross and report the true latitude and apparent longitude (with respect to the grid centre) in the SunGrid window, bottom right. Both are reported in decimal degrees. The true longitude is obtained by adding the parameter Lo to the apparent longitude.
Obtaining SunGrid
SunGrid is supplied free of charge without any warranty whatsoever. The responsibility for any consequences arising from using it lies entirely with the user. It may be freely distributed to anyone provided it is done at no cost to the recipient and the author's name is not removed from any part.
The program may be obtained from here: sungrid_distro.zip
SunGrid is a MS Windows (c) based VB.NET program for digital astrophotographers who specialise in imaging the Sun. It is used to locate features on the sun, such as sunspots, faculae etc. in terms of their latitude and longitude on the sun’s surface. It is based on the idea of a Stonyhurst Disc. (How a Stonyhurst Disc is used is well described on page 69 of the book “The Sun and How to Observe It” by Jamey L. Jenkins, Springer (2009). ) Note that to measure a solar photograph, the user must be aware of the camera’s orientation when the photograph was taken. This requires the upper or lower edge of the photo frame to lie in the E-W direction. These procedures are described in the book by Jenkins.
To use SunGrid, first click on the SunGrid icon to start it up, then minimise it temporarily to stop it blocking your desktop. Next bring up a digital solar photograph on the computer screen using your favourite viewer and expand it to a convenient size. Restore the SunGrid so it now overlays the photograph. Sungrid is transparent and allows the sun’s image to be seen beneath the grid. The SunGrid window must be repositioned, by dragging the top with the cursor, and resized by “pulling” the window from any of the corners or sides in the usual way to obtain a fit of outer circle of the grid to the sun’s diameter.
If required, the transparency of the SunGrid window may be altered using the slider at the bottom of the window, and the brightness of the grid may be altered using the slider at the top of the window. You probably will not need to touch these.
To use the grid, three parameters are required:
Lo – The heliographic longitude of the centre of the Sun’s disc
Bo – The heliographic latitude of the centre of the Sun’s disc
P – The position angle of the north end of the Sun’s axis of rotation
All of these parameters can be obtained, for any particular day, from the Association of Lunar and Planetary Observers (A.P.L.O.) website at http://www.alpo-astronomy.org/solarblog/ in the section “A.P.L.O. Solar Ephemerides”.
Setting the Bo parameter on SunGrid is achieved through the slider on the left of the window. The current Bo value is shown in the SunGrid window, bottom left (see above figure). Setting the P parameter on SunGrid is achieved through the slider on the right of the window. The current P value is also shown bottom left. Now, positioning the cursor over a feature of the Sun and clicking will mark the position with a cross and report the true latitude and apparent longitude (with respect to the grid centre) in the SunGrid window, bottom right. Both are reported in decimal degrees. The true longitude is obtained by adding the parameter Lo to the apparent longitude.
Obtaining SunGrid
SunGrid is supplied free of charge without any warranty whatsoever. The responsibility for any consequences arising from using it lies entirely with the user. It may be freely distributed to anyone provided it is done at no cost to the recipient and the author's name is not removed from any part.
The program may be obtained from here: sungrid_distro.zip
Download the sungrid_distro.zip file to your desktop (or other convenient location) and double click on the icon to enter the .zip file using the Windows explorer. Enter the SunGrid_Distro directory and double click on the setup program. SunGrid should now install. This may take several minutes if you do not have the required elements of VB.NET installed on your computer (it will download what it requires - please be patient). The program should run straight away and it also puts a link on the Start menu (though you may have to look hard to find it.) I advise that you create a shortcut to the SunGrid executable on your desk top. The program can be uninstalled in the usual Windows manner. (Note the uninstaller does not uninstall the downloaded VB.NET components).
Comment and queries may be addressed to the author at:
stargazy (at) btinternet.com
Note: A Java version of SunGrid may be downloaded or run from here: sungrid.jar
Comment and queries may be addressed to the author at:
stargazy (at) btinternet.com
Note: A Java version of SunGrid may be downloaded or run from here: sungrid.jar