by Dick Land
The Schepens Eye Research Institute
Having traveled to view a dozen solar eclipses, I am often asked, why bother?
Answer: As yet there is no technology that can reproduce what the eye can see.
Since my first (rained out) eclipse I went to in l959, optical capture technology has improved greatly. But several aspects of an eclipse will probably elude technological reproduction for a long time to come. The color is unique. The contrast range is more than three orders of magnitude. The expanse is nearly 180 degrees, from one horizon to another. The human eye seems uniquely adapted for enjoying this phenomena, with its scanning system, adjustable gain, central high resolution, color resolving system, and most peculiar of all, a storage system, albeit short-term, such that we think we see the whole sky. Always the black, unlit face, of the moon surrounded by the corona looks gigantic, very like the “moon illusion”, as we stare, the central feature “fills our field of view.” Actually the eye has to scan since it subtends several degrees either side of the half degree central disk. This scanning is an advantage since it allows the variable gain to adjust to the extraordinary brightness range. When looking at the black sky at the ends of the streamers, our sensitivity is increased, when looking close to the limb where the bright red prominences are observed the sensitivity is least. Our mind composites these scans during the brief minutes of totality at a resolution that rivals telephoto lenses and the best films. But our eyes handle the contrast in a locally adjusted manner, very distinct from the typical radial gradient filters, and indeed, most filter programs used to enhance eclipse observations these days.
Yes, during the February eclipse in the Caribbean I managed to photograph both the corona and the planets Mercury and Jupiter in one image. It is not at all like what we saw! The planets were brilliant and showed color against the black sky. The coronal structure extended some two diameters either side of the central disk. The red prominences were nearly overwhelmed by the brightness of the inner most corona. Then off to the west was the even more brilliant Venus, dazzling in the darkness, and directly overhead and difficult to see was the reddish Mars. The span of sky, nearly 90 degrees, makes the human response enjoyed in participating in this experience, awesome.
Colors observed are not reproducible in laboratories here on earth. The corona is gas in a vacuum less dense than we can make, and the energy or temperature is about where our thermonuclear experiments get briefly. The result is emission from highly ionized gas that will elude our laboratories for decades to come. Ah, the red of the prominences – this is hydrogen emission, and yes the color can be made in laboratories.
But should any of this matter? Yes! When we look at phenomena our experience seeing informs us about structure. Many illusions, like mirages, give us miss-information. We have learned to correct or ignore such circumstances. But for the brief spectacular view of the solar atmosphere, we are seeking to understand a great three dimensional flow of energy in which our planet earth has to survive. The apparent structure of the streamers and their directions, perhaps toward us or away from us, now when understood in relation to – say the SOHO , sun tracking satellite, images – suggests the volume filling flow we call the solar wind. Corruption of this view makes understanding difficult or impossible.