{"id":1646,"date":"2017-01-22T16:13:02","date_gmt":"2017-01-22T16:13:02","guid":{"rendered":"http:\/\/www.popastro.com\/main_spa1\/solar\/?page_id=1646"},"modified":"2023-01-24T11:17:59","modified_gmt":"2023-01-24T11:17:59","slug":"2-looking-at-the-sun-safely","status":"publish","type":"page","link":"https:\/\/www.popastro.com\/solar\/solar-observing-guide\/2-looking-at-the-sun-safely\/","title":{"rendered":"2. Looking at the Sun safely"},"content":{"rendered":"

PROJECTION:<\/strong>
\nHow 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\u00a0way\u00a0is to use the “projection” method. Be aware that some telescopes\u00a0have internal plastic parts and these can be damaged by heat by projecting the Sun’s image through them<\/strong>.<\/p>\n

The projection\u00a0method uses\u00a0a 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\u00a0coming from the Sun is considerable but\u00a0projection\u00a0allows us\u00a0to observe the Sun\u00a0safely.<\/p>\n

The first thing that you need\u00a0to do is make either a projection screen, or box,\u00a0to hold\u00a0a 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\u00a0and increase contrast, making it easier\u00a0to see detail on the projected solar image.<\/p>\n

\"solar
Image of telescope pointing skywards, taken by Geoff Elston<\/figcaption><\/figure>\n

The screen\u00a0is 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\u00a0directly to the eyepiece but some prefer to\u00a0attach it directly to the mounting. The projection\u00a0screen\u00a0must be securely attached and not able to fall off or stop\u00a0the tracking\u00a0of the telescope as you follow the Sun.<\/p>\n

A\u00a0projection screen\u00a0will often require a second screen in front of the projection screen\u00a0(see image right) to cast\u00a0a shadow around the eyepiece. This helps\u00a0increase\u00a0contrast of the projected solar image allowing\u00a0you to see more on the projected image of the Sun.<\/p>\n

Once the\u00a0projection\u00a0screen is in place, pick\u00a0a low-power eyepiece and put this in the telescope.\u00a0If your telescope has a finder leave the dustcaps on it. We are ready to start.<\/p>\n

\"Projected
Image of the projected Sun on a screen, taken by Geoff Elston<\/figcaption><\/figure>\n

Aim the telescope in the direction of the Sun. DO NOT LOOK AT THE SUN<\/b>\u00a0 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\u00a0white disk of light on the projection screen.<\/p>\n

Now focus the telescope\u00a0until the round\u00a0image becomes clear. This is the projected image of the Sun, and you will likely see\u00a0some sunspots somewhere on the white disk. The sunspots may be big or very small. There may be very few or many sunspots. The size and number of sunspots varies with the 11-year sunspot cycle. If you can, try to make the size of the projected image 6 inches (152mm) in diameter as this is the standard image size used widely by amateur solar observers.<\/p>\n

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\u00a0the telescope\u00a0every two minutes or so, depending on\u00a0the magnification you are using to keep the image centred on the screen.<\/p>\n

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.<\/p>\n

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.<\/p>\n

\"solar
Image of a solar projection box taken by John Chapman Smith<\/figcaption><\/figure>\n

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 solar projection box was made by John Chapman-Smith.<\/p>\n

FULL APERTURE “WHITE-LIGHT” SOLAR FILTERS:<\/strong><\/p>\n

These\u00a0filters are\u00a0designed\u00a0to enable you to look at the Sun directly through the telescope instead of projecting the solar image. <\/strong>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\u00a0are unlike “Hydrogen-alpha” filters which only allow a specific\u00a0part of the spectrum to pass through them. H-alpha filters are therefore\u00a0\u00a0often called: “monochromatic filters”.<\/p>\n

For a\u00a0white-light solar\u00a0filter to be safe to use it must\u00a0be capable of several things. It must\u00a0block\u00a0infra-red\u00a0radiation (heat) emitted by the Sun, it must block ultra-violet radiation and ithas to reduce the amount of visible light to comfortable\u00a0levels. It must also\u00a0be made so it is possible to securely attach it\u00a0to the front (or aperture) of a telescope without any risk of being displaced or falling off while in use.<\/p>\n

\"solar
Image of a full aperture solar filter securely fitted over the front of a telescope, taken by Geoff Elston<\/figcaption><\/figure>\n

Just because something\u00a0looks opaque or highly reflective\u00a0does not mean it is safe to use as a solar filter. Only use a purpose-made safe solar filter that has been tested and certified as safe to use as your eyesight depends on it.<\/p>\n

Using a full aperture\u00a0solar filter is a must\u00a0if you have a telescope which has\u00a0plastic internal parts. If you have a Maksutov\/Schimdt-Cassegain or other compound telescope then only use a full aperture solar filter as solar projection will damage them.<\/p>\n

These\u00a0types of full aperture white-light solar filters are safe (but always follow the manufacturers instructions):<\/p>\n

Baader Astro Safety Solar Film<\/strong> <\/b>is about the best\u00a0solar\u00a0filter you can get.\u00a0It\u00a0is very safe and gives excellent views of\u00a0sunspots. Personally, I believe it to be better than Mylar as it gives clearer, sharper,\u00a0\u00a0views of sunspots. It must be handled with care but is “pin-hole” resistant as it is usually coated on both sides of the film. It\u00a0can be purchased\u00a0in flat A4 sheets or comes pre-mounted in\u00a0purpose-made filter mounts (you just need to say to the retailer what size aperture scope you have).<\/p>\n

Glass-coated Inconel\u00a0type filters<\/b> as these are\u00a0glass-coated\u00a0mounted solar filters. They tend to cost more due to the use of\u00a0a\u00a0reflective\u00a0coating on one side\u00a0of optically-flat glass. There are a number of manufacturers: Orion, for example, or probably the most well-known is: Thousand Oaks, USA. Their filters\u00a0are available in three\u00a0types: “Type 1” and “Type 2” are used for visual and photographic use,\u00a0“Type 3” is used only<\/b>\u00a0for photography, <\/strong>never for\u00a0visual use\u00a0as the solar image is far too bright to be safe.\u00a0 These filters are robust but can still be damaged by rough-handing and can suffer pin-holes, but if you\u00a0look after them, they will last a\u00a0long time.<\/p>\n

Mylar <\/strong>is a type of aluminised plastic film. It can come in A4 flat sheets or ready-mounted.\u00a0This plastic reflective film is quite tough, but the coating may deteriorate in roughly\u00a0handled.\u00a0 The film\u00a0does give a bluish tint to the solar image but this colour cast can be removed during digital processing. Always check Mylar\u00a0before use to\u00a0ensure there are no pin-holes or tears in the aluminium coating. If there are any, do not use it but\u00a0replace the film with a new piece.<\/p>\n

ADVANCED SOLAR OBSERVING ONLY:<\/strong><\/p>\n

The “Herschel Wedge” <\/b>(or “Solar\u00a0Diagonal” as it is sometimes called) allows you to observe the Sun in white-light. The Herschel Wedge can only be used with the refractor telescope (never with a reflector or catadioptric telescope).<\/p>\n

This\u00a0is a\u00a0piece of equipment that goes at the eyepiece-end of the telescope and\u00a0looks like\u00a0a normal star diagonal. The\u00a0exception is that\u00a0\u00a0there is a piece of wedge-shaped glass\u00a0inside which is un-silvered. As the Sun’s image hits this glass wedge,\u00a0about 95%\u00a0of the solar energy (infra-red and light)\u00a0is allowed to pass right through it and out the back, well away from the eyepiece.\u00a0Most modern Herschel Wedges have a cover to prevent the heat from accidentally scorching your clothing! The remaining\u00a05% of solar enery\u00a0is reflected upwards towards the eyepiece by the glass wedge. The solar image is still far too bright (and there is still some infra-red there too) so a\u00a0Neutral Density filter and in some a\u00a0variable polarizer filter in between\u00a0the glass wedge and the eyepiece to reduce\u00a0the energy\u00a0to a safe comfortable\u00a0level.<\/p>\n

Herschel Wedges\u00a0can be expensive but they can give breathtaking\u00a0views of the Sun. They are not recommended for the beginner. If you do own one then please ensure you use\u00a0a Herschel Wedge by following exactly\u00a0the makers instructions.<\/strong><\/p>\n

Monochromatic filters such as Hydrogen-alpha\u00a0and CaK scopes do not show you the sunspots very well but they do show the features lying in the middle and lower solar Chromosphere. More here<\/a><\/p>\n

Next: Which telescope is best for solar?<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

PROJECTION: 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\u00a0way\u00a0is to use the “projection” method. Be aware thatRead more<\/span><\/a><\/p>\n","protected":false},"author":17,"featured_media":0,"parent":1643,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_monsterinsights_skip_tracking":false,"footnotes":""},"categories":[],"tags":[],"class_list":["post-1646","page","type-page","status-publish","hentry"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t