Coll The Coll Magazine

Article by J.L. D. (2000)

The 1999 Solar eclipse as seen from Coll
The 1999 Solar eclipse as seen from Coll

The much heralded solar eclipse of 1999 finally arrived on Wednesday August 11th & sadly turned out to be a bit of a damp squib for those who made the pilgrimage to Cornwall, where it would be total. Rain in the West Country meant that umbrellas were the order of the day rather than safety viewing glasses. Here on Coll, where the eclipse would unfortunately only be partial, we were a little more fortunate although early morning cloud led you to believe that this might not be the case. For my part I was keen to try & get a few photographs of the event & the cloud cover that we had turned out to be an asset.

So why do eclipses occur? I hear you cry with one voice. Well it's due to a couple of chance & fortunate characteristics of our own solar system. The Moon for the purposes of this discussion, goes round the Earth (although in truth the Earth & Moon go round a common centre of gravity which happens to be located at a point below the Earth's surface but not at its centre). The Earth-Moon pair in turn go round the Sun.

One fortunate aspect of this arrangement is the fact that on occasions the Moon passes between the Sun & the Earth & in so doing casts a shadow of itself across the Earth. That is not the end of the story for it so happens that although the Sun is about 400 times further away from us than the Moon, it is also about 400 times larger in diameter than the Moon. This is a bit of luck as it makes the Sun & Moon appear to be the same size in the sky. There are a few more considerations but suffice to say that the Moon's shadow is generally less than 160 km (100 miles) wide & if you are on the Earth within that shadow you will see a total eclipse of the Sun. Either side of the shadow you will see a partial eclipse where the Sun doesn't get blocked out completely. Such was the case here on Coll where the eclipse was deemed to be about 75% - 80%, i.e. about three quarters covered.

For my photographic attempt I was going to use a lens combination of 600mm focal length on my camera. Such a telephoto lens will yield a decent size image on the negative. For the benefit of those interested but without going into the mathematics here, the size of the image on the negative of the Sun & Moon is roughly 1/100 (one hundredth) of the focal length of the lens (or telescope) being used. A standard camera lens of (say) 50mm will yield an image size of a mere 0.5mm (half a millimetre). Frankly, this is pathetic & even enlarging it by a factor of 10 would only produce an image size of 5mm on a print. With my 600mm lens combination the image on the negative is 6mm to start with. Enlargement by 10 times would produce a print image of around 60mm (nearly 2.5 inches) diameter. Now we're talking! The next problem was going to be light level. The Sun is bright (& dangerous). Pointing a camera at it will most likely punch a hole through the back of the camera.

My lens combination enlarges the Suns image & spreads the light over a greater area but even so there is far too much light for taking a photograph without a filter. Unfortunately I didn't have a Solar filter which is why I was praying for some light cloud cover to act as a natural filter. And so it was that on the day of the eclipse I set the camera up on its tripod & waited. Initially the cloud cover was too thick & the Sun was obscured from view. Totality was scheduled for about 11:11 am (BST) but I wanted to take pictures about half an hour either side of that. The gods were obviously looking down on me that day because at the appointed time the cloud thinned (albeit erratically) to reveal the Sun with the Moon already taking a 'bite' out of it. The filtering effect of the cloud was spot on & as the island fell eerily quiet with the fading light, I took a series of photos at:- 10:38, 10:56, 11:06, 11:13, 11:16, & 11:28 hrs (BST). The results are shown in the accompanying pictures. Not as stunning as the phenomena seen during a total eclipse & not the detail seen when photographing craters on the Moon but nevertheless I am pleased with the end results & for once I was grateful for a bit of cloud cover.

Coll Magazine - Article by J.L. D.

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