Astronomical Society of Edinburgh
Journal 39

Doing anything on August 11th?

I'm sure that I don't need to tell members that there will be a Solar Eclipse on August 11th. But what are you planning on doing then? I'm sure that some will be going off to Cornwall or further afield to the path of totality and my best wishes go with you.

But for those of us staying in Edinburgh, what plans can we make?

Weather permitting, the Observatory will be open for members of the public to see the eclipse in safety. We will have a couple of telescopes projecting the Sun's image - the only guaranteed safe way of viewing the sun, even when 80% or more is covered by the moon.

Elsewhere in this journal we have included a paper on Eye Safety And Solar Eclipses published by NASA. Please do read it and be careful whenever trying to observe the Sun. There are a lot of myths about 'safe' observing methods - many of which could result in permanently damaged eyes.

If you cannot be at the observatory on the 11th here are some methods I have used to observe the sun recently.

Projecting with a telescope

This is a matter of allowing light to pass through the telescope and on to a screen of some sort (for example a sheet of paper on a clip-board).

It is important to remember, when pointing the telescope at the Sun, that it is not safe to use the finder (which should have its cap on or have the front covered in some way). It is even more disastrous to look through the main telescope - you are likely to go permanently blind. Instead, stand with your back to the sun, and adjust the telescope to make it's shadow as small as possible. When it's shadow is smallest the front of the telescope will be pointing at the sun and the sun's light will be shining through it. Then you can hold your screen in place and adjust the focus to give a clear image.

Generally you will not want a very high magnification for projecting the Sun's image - chose an eyepiece which would allow you to see all of the full moon in the field of view.

If your telescope has a drive you can start it running while undriven telescopes will require constant manual adjustment. But in either case never leave the telescope unattended in case the focused image of the sun drifts off and burns the inside of the tube - or even worse, someone tries to look through the eyepiece.

The image from a refractor is usually directly behind the telescope and you may find it helpful to attach some sort of shade around the telescope or project into a box - to minimise the light hitting the screen that is not from the telescope.

A Newtonian reflector (or a refractor with a 90° elbow mirror) can quite easily be used to project the image to side of the telescope. Careful positioning can allow projection on to a shaded wall or in a doorway or open window.

The image projected on to a screen is quite likely to be amenable to being photographed with a simple camera with automatic exposure setting - just make sure that you are not too close to the screen for the camera's focus. Further information about photographing the eclipse is in the article Eclipse Photography also reproduced from the NASA Eclipse Bulletin.

Projecting from a pair of binoculars

Quite acceptable results can be achieved by projecting from one side of a pair of binoculars (cover the objective of the other side) to a screen in a box. With my 8x25 'Practica Sport' binoculars stuck through a hole cut in an old A4 paper box I can get an image about 2cm across 14cm from the eyepiece. While this is not enough to show any but the largest of sun-spots it will be easy to see the partial phases of the eclipse.

Pin-hole camera

A bit less satisfactory, but workable, method is to use the same box but with a sheet of card instead of binoculars. A single pin-hole in the card results in a 4mm diameter disk - enough to see the shape of the eclipse.

Solar eclipse viewers

There are a number of sources of cardboard specs with filters in them but it is important to remember that they must never be used if they are damaged in any way. Only use those with a "CE" mark indicating that they have been properly tested and approved.

With these you will be able to see the partial eclipse but are unlikely to see any sun-spots.

Castle Photographic, Bank Street (at the top of the Mound) have safe viewers for £1.99. The booklet Preparing for the Solar Eclipse over Britain and Europe by Peter Smith, ISBN 0-9535657-0-X, £2.99 contains a viewer. (I have seen this in Waterstone's Bookshop, at the East end of Princes Street.) I believe that that August issue of Astronomy has a viewer on the cover.

There may be others - but watch out for that CE mark.

Exposed film, smoked glass etc - an easy way to lose your sight

Do not look at the Sun without being sure that the 'filter' has been properly tested and approved. While some people may have been lucky enough to escape serious damage to their eyes when using makeshift 'filters' it has been just that - luck. The lens in the eye is quite capable of focusing harmful radiation on to the retina and causing permanent damage.

Pass this message on to anyone you know who might be tempted to take risks with their eyesight. Its just not worth it. Anyone wanting a look at the eclipse can use one of the safe methods outlined above, or just come and join in the fun at the Calton Hill.

Time of Eclipse

The eclipse will start (in Edinburgh) at 10:05 BST, will reach its maximum extent (over 80% covered by the moon) at 11:18 BST, and will end at 12:33 BST.

Anyone wanting the exact times (to 0.1 second) or for other places in Scotland (or Europe) should refer to "Total Solar Eclipse of 1999 August 11", Espenak and Anderson, 1997. (Available for reference in the Society's Library or online at http://umbra.nascom.nasa.gov/eclipse/990811/rp.html)

Graham Rule