Observing the Sun safely

Credit Lee Macdonald

In this section we provide a guide to amateur astronomers who want to observe the Sun and also to teachers who would like to carry out some solar astronomy at school. The first question one might ask is “Why observe the Sun?”. For a start, the Sun is our local star and it is always changing. It can be observed during that daytime, which is a distinct advantage for school projects and clubs. The Sun can be observed at any time during the year, providing of course that it is not cloudy. Amateurs can make useful observations. Only a relatively small telescope is needed. Light pollution is not a problem.

Warning! Before a description is given of how to make solar observations, there must be a strong warning! Observing the Sun can be dangerous. NEVER look at the Sun directly through a telescope – you could be blinded.

Do not assume that a filter which makes the Sun look dark is safe to look through: it may let through infra-red and/or UV. Only use filters from reputable suppliers intended for solar observing.

Credit Lee Macdonald

Telescopes A refractor is the best all-round telescope and can be used to project an image. A small telescope is best, since it is portable and can be used on short notice. An equatorial, driven mount is desirable but not essential.   Viewing the Sun’s image The Sun’s image can be viewed in projection or with a filter. The advantage of projection is that it is cheap, completely safe, comfortable to view and the Sun can be viewed by groups (good for schools). The disadvantage is that the projection box has to be home-made and it is unsuitable for photography. The advantage of a filter is that it can be used on all telescopes and is good for photography. The disadvantage is that not all filters are safe. Even if a filter makes Sun look dark, it is not necessarily safe. NEVER use eyepiece filters or home-made filters, e.g. photographic film.

For further advice on filters for solar observing download our Beginner’s Guide to Observing the Sun PDF (128K)

Credit Lee Macdonald

Observing Sunspots
Sunspots are regions where the Sun’s magnetic field breaks through the surface (find out more about Sunspots in the Sun|trek section). They appear dark because they are cooler (4000K) than surrounding solar ‘surface’ (6000K). They range in size from tiny pores at limit of professional images to giant complexes several times Earth’s diameter. Sunspots are only the visible ‘tip of the iceberg’ of magnetic active regions, which can be violent enough to affect radio communications and cause aurorae on Earth (find out more about the effects of solar storms in the Sun|trek section)

Credit Lee Macdonald

The Solar Cycle and Counting Sunspots
Solar activity, including sunspots, waxes and wanes in an 11-year cycle ( find out more about the solar activity cycle in the Sun|trek section). We are now (2009) at the minimum of the cycle of solar activity, and on many days no sunspots are visible. The last solar maximum was in 2000, when the Sun was heavily-spotted on most days. The peak of the next solar maximum is predicted to occur in about 2012, but the number of sunspots will start increasing well before then.

One solar cycle is never the same as the next and an important task for the amateur solar astronomer is to monitor the Sun for changes. At the moment (2009) there are very few, if any, Sunspots on the Sun, but soon the number will start to increase and by 2011 there should loads!

For more details about solar photography download our Beginner’s Guide to Observing the Sun PDF (128K)

The Solar Chromosphere
The Sun has an atmosphere, which is in two parts: the corona (outer atmosphere) (find out more about the corona in our Sun|trek section) and the chromosphere (inner atmosphere) (find out more about the chromosphere in our Sun|trek section). The corona is not visible from Earth except during a total eclipse or with aspecial telescope called a coronagraph. The chromosphere can be observed with special (and expensive) filters known as H-alpha filters. In the chromosphere we can see some of the activity surrounding sunspots.

H-alpha filters

H-alpha equipment is expensive, but less so than it used to be. Prices now start at around £500. The Intitute of Physics (with STFC) runs a grant scheme for schools which teachers could apply to (Find out more about this grant from the IOP here). The Sun can be observed in H-alpha using a dedicated H-alpha telescope (e.g. Coronado PST) or H-alpha filters adapted to an existing telescope. Filters made by Coronado, DayStar, Lunt and Solarscope show disc features and prominences.

Prominences
The Baader coronagraph can be used to show prominences (find out more about prominences in the Sun|trek section). It uses an occulting disc to ‘eclipse’ the Sun. A coronagraph is ideal for photographing prominences, although other H-alpha filters can be used as well. A coronagraph gives a bright image – and so allows short exposures with small telescopes

Going further

If you are keen on observing the Sun, or any other aspect of astronomy, it is a good idea to join a local astronomical society. Such a society is very likely to have experienced members, who will be able to give you much valuable advice on solar observing. Some societies also give talks and astronomical advice to schools. A search on the Internet or an enquiry at your local library should find the nearest astronomical society to you.

The best national society for beginners is the Society for Popular Astronomy (www.popastro.com). For more advanced observers, there is the British Astronomical Association (www.britastro.org). Both societies have active solar sections, which will be able to guide you and offer advice on more advanced techniques than have been discussed here.

International Year of Astronomy Solar Physics Group

The IYA2009 Solar Physics Task Group webpage provides lots of useful information and the solar oriented activities.   http://solarastronomy2009.org/