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ECLIPSES SOLAR an eclipse safely How to observe SOLAR ECLIPSE, OCTOBER 2014, BY LEMAN NORTHWAY Solar eclipses are quite rare and are often a major event. The SOLAR ECLIPSES Moon passes right in front of the Sun, blotting out its disc. Every time a solar eclipse occurs there are various things to look for. However, it is extremely dangerous to just go out and look up. The Sun is so bright that just looking at it can blind you, so you’ll need to prepare beforehand. There are various ways to observe eclipses safely, using both everyday materials and telescopes or binoculars. So read this leaflet Introduction to find out what happens during an eclipse and how you can see all the stages of the event safely. This booklet was written by the Royal Astronomical Society with The Society for Popular Astronomy and is endorsed by the British Astronomical Association The Royal Astronomical The Society for Popular Formed in 1890, the Society, founded in Astronomy is for British Astronomical 1820, encourages and beginners of all ages. Our Association has an promotes the study of aim is to make astronomy international reputation astronomy, solar-system fun, and our magazine, for the quality of science, geophysics and Popular Astronomy, is full its observational closely related branches of information to help and scientific work. of science. you get to know the Membership is open to www.ras.org.uk sky and get involved. We even have a special Young all persons interested in HIGGS-BOSON.COM JOHNSON: PAUL BY D Stargazers section, run by TV’s Lucie Green. astronomy. www.popastro.com www.britastro.org DESIGNE When the Sun goes out solar eclipses would happen every month. A solar eclipse occurs when the Moon However, as is often the case with science, comes between the Sun and the Earth and things are a little more complex than casts a shadow on Earth. Anyone within a that, because the Moon’s orbit around the certain area will see the Moon cross in front Earth is tilted compared with the Earth’s of the Sun. In a very narrow band across orbit around the Sun, and both orbits are the Earth’s surface, the Moon passes squashed into an ellipse. So for an centrally in front of the Sun’s disc, eclipse to occur, the Moon has to be completely blotting it out for a “You’ll in the right place at the right time. remember it few minutes – this is a “total solar Because the Moon is smaller for the rest of eclipse”. Over a much wider area, than Earth, its shadow during an your life” the Sun is only partially covered eclipse covers only part of Earth’s by the Moon – a “partial eclipse”. It’s surface. So although there are always not as spectacular, but it’s a great thing to at least two solar eclipses a year, from watch, and something you’ll remember for any one spot you usually see a solar eclipse the rest of your life! only every few years, usually a partial Solar eclipses do not happen very often eclipse, though it may be total elsewhere. because the conditions are quite specific. See http://astro.ukho.gov.uk/eclipse for If the orbit of the Moon was in the same information on future eclipses. ● plane as Earth’s orbit around the Sun, total total eclipse (umbra) partial eclipse (penumbra) Sun Moon Earth How a solar eclipse works A solar eclipse occurs when the Moon comes between the Earth and the Sun and blocks out the light from the Sun. As the Earth and the Moon continue to move in relation to the Sun, the area of the total eclipse moves across the surface of the Earth. Thus the eclipse can be seen at different times from different parts of the world. N( ote that the diagram above is not to scale.) What is a solar eclipse? a solar is What Did You Know? The last total solar eclipse visible from the UK was in 1999, when thousands of people flocked 1: to Cornwall to catch a glimpse. But for most of them it was cloudy. Just a few places saw the event through a break in the clouds. What is a solar eclipse? (cont.) Solar eclipse buzz words First contact The moment when the not a solid surface but is actually a layer Moon first starts to block the Sun and the about 500 km thick, which is very thin first small “bite” appears in the edge of the seeing as the Sun is 1,391,684 km across. Sun. The photosphere is completely covered during the total eclipse. Second contact The moment during a total eclipse when the Sun is completely Chromosphere Above the photosphere covered by the Moon. is a pink-red layer of gas, about 2500 km thick, known as the chromosphere. Totality The period of time (usually a few During totality it is possible to see the minutes) in a total eclipse after second chromosphere in detail, as a ring around contact when the Sun is completely the darkness of the Moon’s silhouette. blocked by the Moon and a small part of the Earth is in full shadow. Baily’s Beads Because the edges of the Moon are not perfectly smooth, at the Partial phase The period of time when start and end of totality some sunlight only a section of the Sun is blocked by the shines through the valleys between Moon. In the UK none of us will see the mountains, with the appearance of beads. Sun completely covered, so the eclipse These are called Baily’s Beads after the will be partial throughout. scientist Francis Baily. Third contact The moment in a total Diamond Ring During a total eclipse, eclipse when the Sun reappears from if only one of Baily’s Beads is shining, a behind the Moon. Diamond Ring effect can be seen around Fourth contact The moment when the the lunar silhouette. Sun is completely uncovered again. Annular eclipse This occurs when the Photosphere The visible “surface” of Moon’s disc is smaller than the Sun’s, so the Sun. As the Sun is gaseous, this is the Sun is not fully covered. When is the next eclipse? ● To find global circumstances and animations of the Earth for locations across the globe, visit http://astro.ukho.gov.uk/eclipse. ● To find the exact viewing conditions and watch an animation of what to expect a solar eclipse to look like where you live, visit http://www.timeanddate.com/eclipse/solar. Safety first around the edge of the Sun. During totality, Remember, you can only view the eclipse the sky goes dark. If it is cloudy, you might using suitable filters or projection methods not notice a huge difference. But if it’s clear, – see section 3. when you look at shadows in the landscape, There are so many special features particularly at maximum eclipse, you may associated with solar eclipses because each see that they will have an odd shape, being one is unique due to weather conditions, sharper in one direction than another. location and several other factors. But, once During totality the temperature can change you’ve seen one, you’ll be smitten! and it can feel colder, animals go quiet and Totality only occurs in a narrow path birds may stop singing. across the surface of the Earth. At the If you have a telescope and are projecting midpoint of time of totality, which the image (see section 3), or are is known as the maximum point “You’ll viewing it using a safe solar filter, of the eclipse, it can go dark have to wait you may notice that there are (like twilight) for the duration. until 2090 to see dark spots on the Sun: sunspots. Away from the path of totality, a total eclipse These are places where the Sun’s from mainland the same eclipse will be a partial magnetic field restricts its light UK” solar eclipse of varying degrees, output. Although sunspots look visible across a region thousands of black, they are still part of the Sun and kilometres wide. if the Moon’s disc happens to cross one you An eclipse begins with first contact. You could notice that the Moon’s disc is darker can’t see details on the disc of the Moon, than the sunspot. or the whole of the disc, during a partial Also look at the edge of the Moon eclipse – all you see is that a bit of the bright (known as the limb) and you might see Sun is missing. It may take a minute or so that it isn’t completely smooth, as you before you notice it. can see mountains or valleys on the limb The Moon continues to move ever so silhouetted against the Sun. But you’ll slowly across the Sun until second contact probably see a lot of shimmering at the Whatsee you’ll is achieved. This is when the entire disc limb, which is caused by turbulence in of the Sun becomes covered by the Moon. our own atmosphere rather than anything The total eclipse begins at second contact. astronomical. Observers may also be able to see Baily’s Observers may be able to see Baily’s 2: Beads and the diamond ring effect, which Beads and the diamond ring effect again, occur just before totality. just as totality ends. During totality, which is the maximum Third contact is when the total eclipse eclipse, the Moon entirely blocks the face ends and the Moon starts moving away of the Sun.
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