Annular Solar Eclipse in Spain, 3rd, October, 2005: Eclipse light curve
I tried to obtain some photometric data in the annular eclipse from last 3rd, October in Spain. The method was simple: Only a compact digital camera was used (Olympus C-5050) adjusted in program mode. In fact, any digital camera able to show the used exposure values (shutter speed and f-stop) serves for this type of undertaking (in my experience the Olympus C-2000, for example, would have worked perfectly well, and it can be had for about 60$ or less these days on E-bay).

The camera was aimed always at the same area of grass in the hotel’s garden where we watched the eclipse, without varying the focal length of the lens, that is, without changing the zoom adjustment.

As you can see in the following charts, there is a small lack of continuity in the produced curve, probably due to some irregularities while recording the data. Although the grass is a more or less uniform source of reflected light, it would have been better to use a standard photographic grey card.

Scrolling down this page you can also see an interpolated curve using “CurveExpert” software and even download a file in MS Excel format where you can see the raw data and the performed calculations.

A more serious procedure for obtaining better results would have needed to take into account Airmass, but hey, nobody gave us a grant for researching on this :). In any case, I think that the important thing is to realize that simple equipment, sometimes, produces very interesting results.

Luis Argüelles

Figure #1: Processed data. Exposures values (shutter speed and f-stop) were normalized for f/4

Figure #2: Light Curve: Note some irregularities probably due to some deviations while gathering the
experimental data. In any case, the overal behavior of light intensity along the eclipse is clear
Figure #3: Fit of data using CurveExpert Software

Just click here to download the raw data and performed calculations in MS Excel format