Pete Lawrence is your guide to making safe visual observations of our nearest star this summer
Observing the Sun in white light is rewarding and relatively simple to do. It’s also inexpensive, especially if you already have a telescope; all you need is a white-light solar filter. There are many different ways to make a record of white-light solar activity, including simple counts of surface features, full-disc images, generic sunspot classifications and detailed classifications. In this article we’ll guide you through solar observation, from the basics to performing detailed, daily sunspot classifications. Your observations will really help solar science, and don’t forget that this is a unique opportunity to study a star close up!
First, though, we have to address the issue of solar safety. Concentrating the Sun’s energy through a lens or with the concave mirror of a reflecting telescope raises it to potentially dangerous levels, so never look through or point any unfiltered telescope directly at the Sun. This includes small finder telescopes too, as apart from the obvious fire risk, there’s a good chance you’ll burn out their crosshairs. We’d recommend capping, filtering or removing finderscopes just to be sure.
A certified white-light solar safety filter fitted over the front, open end of the telescope reduces radiation levels, making the Sun suitable for direct observation. Ready-made full-aperture solar filters can be ordered for your scope size or you can buy certified solar safety film at relatively low cost and make your own full-aperture filter. If you have a large scope, larger rolls of film are available or an alternative is to make an offset aperture filter. This is a large piece of opaque card that covers the full scope aperture with a smaller circular opening cut in it, which is covered with the solar filter. If your scope has a secondary obstruction, the opening needs to be offset from the centre. Always make sure to check the filter before you fit it. If it’s ripped or lets light through, discard it and buy or make another.
Get to know the features
With the filter fitted to the scope, it’s time to turn it towards the Sun. The best way to do this is to look at the shadow of the scope on the ground, adjusting the scope’s position until the shadow size is at its smallest. If you’re using a neutral density (ND) 5.0 or higher film, you can view the Sun through the eyepiece. Most DIY filter
