What do a tree, a colander and a piece of cardboard have in common? The answer: they can all be used to observe a solar eclipse!
Our Sun – the brightest star in the sky – has been the subject of intense scrutiny ever since human beings began to interrogate the world around them. As individuals, we depend on it for light and warmth as we go about our everyday lives.
Never does the Sun attract so much public attention as during a solar eclipse. This is when the Moon appears to take a bite out of the Sun or, on rare occasions, hide it completely. We can now predict eclipses to the nearest second thanks to the availability of historical records going back millenia.
Solar eclipses present opportunities to observe – and image – the disk of the Sun safely using ordinary household items, no telescope or filter needed. Indeed, unless you are an experienced solar observer and know exactly what you are doing, it is extremely ill-advised to look at the sun through any sort of optical instrument ever for a brief period – your eyesight is much more valuable than any measure of enjoyment you might obtain.
There are, in fact, much safer ways to observe the Sun without having to invest in astronomical instrumentation. These rely on the fact that the Sun is very very bright and use the pinhole camera principle.
This is how it works: Take a piece of cardboard and make the tiniest hole using a pin, the tip of a sharpened pencil or a pen. Then project the Sun – you do need a sunny day for this – through the hole onto a sheet of white paper or another piece of white cardboard. Ideally, you should see a nice, sharp circular disk of light on the sheet -that’s the Sun. If you don’t, experiment with moving the sheet to and fro. You may find that, if the sheet is too close to the hole the image is too small, if it is too far the disk is too faint. If the image is too faint and too small, try making the hole a tad wider to let more light through.
Take care not to make the hole too large – more than a few mm across, say. If you do, the image of the solar disk may become blurry or indistinct, then you will have to start again!
For those wishing to try their hand at making your own pinhole camera, there is quite a number of step-by-step guides available online. Here is a selection:
Interestingly, the pinhole camera principle would also apply to other kinds of apertures, for instance the holes on a colander or the gaps between tree leaves in dense foliage that the sun can shine through. The pictures shown below were taken by the author from near the town of Agrinion, Greece, during the 4th January 2011 partial eclipse of the Sun. At that time up to two-thirds (67%) of the disk was hidden by the Moon. Similar vistas await us come June when the Sun will lose about 45% of its disk on the morning of Thursday the 10th of the month. More details about this event may be posted on this forum shortly.