|Help and Advice|
|Transit of Mercury 2016|
|Giving long exposures on a digital camera|
|Photographing star trails|
|Predicting the ISS and other satellites|
|Using a mirror to view a partial eclipse|
|Simple Guide to Viewing the Space Station|
|Choosing a Telescope|
|Tips when projecting the Sun|
|Starting to Use Your Telescope|
|Imaging with a DSLR through the telescope|
|Buying a telescope for a child|
|Photographing a partial eclipse|
How do we look at the Sun with a telescope without harming our eyesight? We can use solar filters (more on this later) but for the beginner the safest and simplest way is to use the "projection" method. Be aware that some telescopes have internal plastic parts and these can be damaged by heat by projecting the Sun's image through them.
The projection method uses a telescope to project the image of the Sun onto white paper or card and we look at the projected image of the Sun instead of looking at the Sun directly. The amount of energy coming from the Sun is considerable but projection allows us to observe the Sun safely.
The first thing that you need to do is make either a projection screen, or box, to hold a white surface behind the eyepiece of the telescope. In some ways a projection box is often a better choice, as it will darken the projection screen and increase contrast, making it easier to see detail on the projected solar image.
The screen is best attached to telescope so it will remain behind the eyepiece as you move the telescope. Normally, you can attach the projection box or screen directly to the eyepiece but some prefer to attach it directly to the mounting. The projection screen must be securely attached and not able to fall off or stop the tracking of the telescope as you follow the Sun.
A projection screen will often require a second screen in front of the projection screen (see image right) to cast a shadow around the eyepiece. This helps increase contrast of the projected solar image allowing you to see more on the projected image of the Sun.
Once the projection screen is in place, pick a low-power eyepiece and put this in the telescope. If your telescope has a finder leave the dustcaps on it. We are ready to start.
Aim the telescope in the direction of the Sun. DO NOT LOOK AT THE SUN but instead, watch the shadow of the telescope on the floor, etc. Once the shadow has become small the telescope will be pointing at the Sun, and you should see a fuzzy white disk of light on the projection screen.
The image of the Sun will move slowly across the projection screen from right to left due to the rotation of the Earth. If you have an altazimuth mounting, you will have to move the telescope every two minutes or so, depending on the magnification you are using to keep the image centred on the screen.
Try various eyepieces to see what happens at different magnifications. A higher magnification will make the Sun drift quicker across the screen and will make the Sun's disk bigger meaning you won't see all of the solar disk at once. However, you will then be able to see more detail in the sunspots themselves.
Lastly, never leave a telescope unattended while it is pointing at the Sun with a projection screen or box. Be careful, if there are children present, that they don't try to look through the eyepiece while it is pointing at the Sun.
A solar projection box is another way of safely looking at the Sun. The projection box in the image here is made of balsa wood, some long wooden dowels cut to the right length (about 30cm) and some thin black or grey card. The whole lot is glued together and the card is wrapped around the outside (to act as a shade) and taped in place. The whole box is so lightweight it can be attached directly to the eyepiece. It is trapped between the eyepiece itself and the eyepiece tube (the eyepiece being held in place by the small chrome thumbscrew). This excellent solar projection box was made by former SPA Solar Section Director, John Chapman-Smith.
These filters are designed to enable you to look at the Sun directly through the telescope instead of projecting the solar image. These filters are called: "white-light" solar filters because they allow all of the colours in the spectrum through (but at greatly reduced intensity). Whit-light filters are unlike "Hydrogen-alpha" filters which only allow a specific part of the spectrum to pass through them. H-alpha filters are therefore often called: "monochromatic filters".
For a white-light solar filter to be safe to use it must be capable of several things. It must block infra-red radiation (heat) emitted by the Sun, it must block ultra-violet radiation and ithas to reduce the amount of visible light to comfortable levels. It must also be made so it is possible to securely attach it to the front (or aperture) of a telescope without any risk of being displaced or falling off while in use.