A beginners' guide to solar observing

With a little eye protection, our nearest star offers up some exciting viewing opportunities

A
a
-

The Sun, our source of natural light and warmth, and the star that made life possible on our planet, is just next door in astronomical terms. It’s only, on average, 150 million km away.

It’s possible to get great, close-up views of our star with the right equipment, but it’s really important to realise that the Sun’s intense heat and light can be very dangerous if not treated with respect. Never observe the Sun with any optical apparatus that has not been fitted with a proper solar filter. Don’t use sunglasses or layers of photographic film – it’s just not worth the risk.

So what is a proper solar filter?

For starters, it’s very dense. It has to be able to filter all visible wavelengths to a safe level, as well as blocking infrared and ultraviolet light – all wavelengths that can cause permanent damage to the eyes.

One of the simplest ways of looking at the Sun is to get hold of some welder’s glass. To be dense enough it should be a grade 14 shade. With one of these placed in front of your eyes before you look at the Sun, you’ll be able to see any large sunspots and watch solar eclipses safely. There are also cardboard eclipse viewer glasses, with which you can safely get the same views. But make sure they are absolutely clean and scratch-free.

If you want to get more than just a safe, naked-eye view of the Sun you’ll need something a bit more substantial than basic protection. With a telescope or binoculars on a tripod, you can project the Sun’s image onto a large piece of white card to see features on the photosphere (its visible surface). The card is simply placed in front of the eyepiece where your eye would normally go. Once everything is set up, and after some focusing, you can easily see any sunspots.

You can also get safe solar views through reflectors and refractors by fitting a solar filter over the front, objective end of the telescope. These cut out all of the ultraviolet and infrared radiation (heat) from the Sun and also 99.9 per cent of its brightness, so the internal workings don’t heat up. Solar filters are made from materials such as aluminium-coated Mylar, or coated glass – but do get advice from a reputable dealer. It’s important never to use a solar filter that screws into an eyepiece. These are very dangerous because they sit at the point where the full power of the Sun is focused and could shatter and let in blinding sunlight.

There are also specialist solar telescopes. The most popular and affordable of these is the Personal Solar Telescope, or PST, from Coronado. This shows just one wavelength of light – the most active – that’s given off by hydrogen atoms. This will reveal features such as prominences and filaments – solar activity that is invisible when projecting the view or using solar filters.


Solar safety

Solar observing is the one time that astronomy poses a real risk of physical injury. Here’s how to do it safely...

Solar Projection

All you need is a piece of white card, onto which you project the image of the Sun from your scope or binoculars. You could also fix another piece around the front end of the scope to create a shadow around the projection. Good for eclipses and sunspots. Cost: free


Cardboard sun projector

These kits are simply a small telescope and mirror that projects an image of the Sun onto a white screen on the inside of the box. It will show much the same views as the solar projection setup – great if you don’t have a scope.
Cost: from £49


Solar filters

These glass or film coverings fit completely over the light-gathering front end of the scope, stopping all heat and virtually all light from the Sun entering the scope. Good for viewing sunspots and granulation. Cost: film filters from £40, glass filters from £70


Personal Solar Telescope

The Personal Solar Telescope (PST) is made to reveal one specific wavelength and can show much more than your naked eye will see with film or glass filters. Good for prominences, active regions, filaments and faculae. Cost: from £480


What you’ll see...

 

Prominences

A prominence is a dense cloud of material that can be seen just outside the bright photosphere of the Sun. The gas is created and held there by the Sun’s vast, arching magnetic fields. Best seen with a PST.


Sunspots

Sunspots are caused by immense magnetic fields. These reduce the temperature of regions of the photosphere producing dark spots. You can see them with solar projection, a PST or solar filters.


Filaments

A filament is the same as a prominence, except that whereas prominences are seen outside the Sun’s disc, filaments are seen against the disc – which makes them a little harder to pick out. Best seen with a PST.


Flares

Flares are the most explosive features on the Sun and are associated with sunspots. They are believed to be caused by sudden changes in the Sun’s magnetic field. They are best seen with a PST.


This article originally appeared in the June 2011 issue of Sky at Night Magazine.
 

Like this article? Why not:
Where to see the Transit of Venus
previous feature Article
The 2012 transit of Venus guide
next feature Article
We use cookies to improve your experience of our website. Cookies perform functions like recognising you each time you visit and delivering advertising messages that are relevant to you. Read more here