Total Eclipse of the Sun

29 March 2006

Image processing reveals the exquisite structure of the corona


Image 1: First Contact plus 4 minutes ... Image 10: Second Contact minus 1 minute


Second Contact

Note the prominence at 11 o'clock


The poles of the Sun's magnetic
field can be seen at 1 and 7 o'clock

Third Contact

More prominences can be seen

The following sequence of images shows how raw images can be processed to create an image
that reproduces the appearance of the corona as seen by the naked eye or through binoculars


A single raw image (exposure 1/15 s) shows
the outer corona reasonably well but shows
no detail in the inner corona as this has saturated


Taking the difference between the raw image
and a smoothed copy of the image (called an
'unsharp mask') reveals fine structure in the corona


Combining a raw image with a composite of
difference images (taken at various exposures)
shows detail not seen in the raw image alone

Changing the gamma (the mapping between
pixel values and pixel intensities) shows
more of the streamers in the outer corona

[ Note that the ghostly circle of light seen in the lower left of these images is a reflection of the very bright inner corona.
The inner corona is 1000x brighter than the outer corona, and even multicoated lenses will reflect some of this light. ]

Technical details:

Nikon D70 digital SLR camera
Sigma 100-300mm f/4 lens with x1.4 teleconverter (equivalent to 420mm f/5.6)
Exposures vary from 1/4000 s for the bright prominences and inner corona to 1/4 s for the outer corona
The solar corona varies in brightness by many orders of magnitude at different distances from the Sun's
surface (photosphere) and so no single exposure can capture all of the detail seen by the human eye.
The image at the top of this page is a composite of five exposures ranging from 1/250 s to 1/4 s.
The image processing was carried out using the freeware application Image SXM.


Sahara Desert, Libya
Longitude: 21° 31' 13'' E
Latitude:   28° 14' 34'' N


First Contact

09:08:41 UT

Second Contact

10:26:38 UT

Third Contact

10:30:41 UT

Totality 4 m 03 s

Fourth Contact

11:50:12 UT

Photos taken during the cruise to and from the eclipse site in Libya,
including the elusive green flash at sunset, can be found

Steve Barrett    May 2006

All images © Steve Barrett 2006


Back to top