Spiders Web Graticule

 I like to make daily drawings of the sun, using the projection method and a screen with a circle the same size as the solar image divided into squares, 8 by 8. When looking through an eyepiece with a white light or H alpha filter, it can be difficult to accurately relate features seen with those drawn from the screen grid. What is needed is a graticule, having a grid the same size as the solar image seen with a particular objective.

I had heard a legend when I lived in York that Cooke, Troughton and Simms used to send people out to collect spider webs on nearby Haxby Common, for their graticules. It probably was untrue but I thought for long enough, “why not?”  My garden is full of spiders at this time of year. Collecting the material is tricky and fitting it is more so, but the result is worth the effort as it produces a very fine and straight line at the focus of my 20mm eyepiece. The main web support is the stuff to use, it’s not sticky, is stronger and can be glued in place with a dab of glue.

I collected my pieces by wrapping it round a piece of stiff wire bent into a large hairpin shape, gluing it on and then each strip was put onto a holder that fitted into the bottom of the eyepiece, gluing each strip as it was applied.  The dimensions need to be worked out first; the image size is sine 0.5 degrees times the focal length. I find it makes accurate positioning easy and I’ve not yet had complaints from the spider’s union!

 Brian Mitchell.

N.B.  I think the ‘legend’ is in fact true as members of the York AS went out to prove it could be done and demonstrated that it could.

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