Monday, June 27, 2011

Solstice Sun Alt-Azimuth

I've finally got some preliminary results for the Solstice observations last week. The high for the day was 105°F (41°C) and NIO had to shut down due to overheating after being exposed to direct sunlight for about an hour. The solution was to hang a towel over him and to provide some additional shade for the wrist wacth between photos. Since then NIO has been helping with the photo analysis by locating the positions of the corners of the 1 inch square grids as well as the grid coordinates of the Sun's position. The position of the camera was lowered closer to the plane of the graph paper and 14 megapixel images were captured. An example of one of the clipped images is shown below along with expanded views about NIO's coordinates for the corners. He used the intersecting line method to locate the corners but got confused when light from the Sun or outside the shaded region changed the appearance of the lines so some corrections were necessary.

The position of the Sun was found by determining the upper, lower, left and right bounds of the image of the Sun. The grey scale of the clips were "stretched" to make the grid lines and the Sun easier to see.

The grid coordinates of the Sun's image were used to find the Sun's altitude and azimuth as a function of the time. The height of the lens aperature was found by measurement to be 24.8 inches. A check against my longitude turned out to be worse than expected being almost 1 degree off. I set the wrist watch to UT just before starting the observations. Time was measured to the second so its precision was about 1 part in 3600. The μ coordinates were rather flat and so its errors were probably more significant. They may have thrown off the time of the peak slightly.

Supplemental (28 Jun 2011): The "platform" I used was warped being shaped somewhat like an inverted bowl. I noticed some curvature when leveling the platfrorm with a spirit level and tried to compensate for it. This is probably the major source of the error in the observed latitude and longitude since the measurements are relative to the platform and its grid system.

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