Solar Eclipse
If the Sun is much bigger than the Moon, why does the Moon appear to be the same size as the Sun during an eclipse?
Find out here.
How can we see the eclipse?
How can we make our own viewers to see the eclipse?
Model your own eclipse!
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Relative size of the Sun and Moon
If the Sun is much bigger than the Moon, why does the Moon appear to be the same size as the Sun during an eclipse? This is a question that is frequently asked and is best explained with some simple modeling.
Take a soccer ball, (or any other large ball such as a basket ball, beach ball, etc.) and a cricket ball, (again any smaller ball such as a tennis ball, baseball etc. will do).
Place the soccer ball on a table, or get a friend to hold it up. Stand about 2m away from the soccer ball and hold the cricket ball in front of you as shown in
the figure below. Move the cricket ball backwards and forwards and you will find that in one position the cricket ball appears to be the same size as the soccer ball.
During an eclipse of the Sun, the Moon only appears to be the same size as the Sun for the same reason. The Sun is in fact very much larger than the Moon, but it is also very much further away.
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Never look directly at the Sun
Looking directly at the Sun can blind you and even a quick "peek" can cause permanent damage to your eye. The only safe way to look at the Sun is to project the Sun's image onto a screen or to use an approved device such as a solar viewer from the Observatory. Do not use foil from crisp packets, exposed negatives, stiffy from a computer. The only safe way to look at the Sun is to project the Sun's image onto a screen and look at that or else use a properly designed and approved solar viewer. These will be available from observatories and planetariums. There are several ways in which the Sun's image can be projected onto a screen.
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Project the Sun's image onto a screen -
do it yourself!
1. Pinhole.
Take a large cardboard box and cut out a piece large enough to put your head through as shown
above. Cut a smaller hole in one end and glue a piece of kitchen foil over it. On the opposite end, glue a piece of white paper to make a screen. Use a pin or a small nail and carefully make a small hole in the kitchen foil - it should be 1mm or less in diameter.
Align the box so that the pinhole faces the Sun, move the box around until a bright patch of light falls on the screen. This is an image of the Sun. Put your head into the box to study the small image at your leisure. The longer the box the larger your image will be.
Another way that a pinhole can be used is in a room that can be darkened and has a north facing door or window. Darken the room and cover the window/door with some dark cloth, cardboard or black bags. The make a small hole as high up as possible as shown
below. The Sun's image can then be seen on small piece of stiff card covered with some white paper. The advantages of this method are that a larger number of people can see the image and that it will be larger than the one seen in the box.
2. Optical Projection
Never look directly at the Sun through binoculars or a telescope.A pair of binoculars can also be used to project an image of the Sun onto a screen. Take a piece of card and cut two holes in it so that the ends of the binoculars stick through the card. Cover one of the lenses of the binoculars with some kitchen foil as shown
below. The card and binoculars can be mounted a tripod and an image of the Sun projected onto a screen as shown below.
3. Large scale projection
The sunlight that falls onto the mirror is reflected onto the wall some distance away to produce an image. All the sunlight collected by the small mirror is now spread out over a much larger area and the image is dimmer.
If a small mirror is used to project an image of the Sun onto a south facing wall or the south side of a large building 50m or more away, then a large image of the Sun will be seen,
as shown in the picture below. This is because the small mirror acts like a large "pinhole", and the further the mirror is away from the wall the larger the image will be. The image will not show a great deal of detail and it will be much dimmer
but a very large number of people can see the progress of the eclipse.
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