A total eclipse of the sun! Well…almost!

Total Solar Eclipse Bangladesh 22 July 2009 CC-BY Lutfar Rahman Nirjhar


By Becca Smithers

Here in the UK on 20th March between 8:35 am and 10:41 am there will be a massive partial eclipse of the sun.

The further north you go, the moon will obscure more and more of the sun. In Penzance about 88% of the sun will be blocked out, and up in Aberdeen around 94% of the sun will be obscured.

This blog helps you make your own pinhole camera so that you can view it safely before exploring what causes a solar eclipse.


Activity: Build a pinhole projector

It is very important that you do not look directly at the eclipse! The ultraviolet light given out by the sun can damage your eyes. This does not mean that you should miss out on this phenomenon.

To view the eclipse directly you could order yourself some eclipse glasses, which are available online. Eclipse glasses are not like normal sunglasses, they have extra dark lenses to filter the UV light to protect your eyes, only use C E approved eclipse glasses. Unfortunately these glasses degrade over time and even a tiny scratch on them could mean damage to your eye. Alternatively, you can make a pinhole camera to project the eclipse on to a bit of paper!

Things you will need:

  • A large piece of paper or card
  • A pin or a sharp pencil

It is very simple to make a pinhole camera. All you need to do is make a small hole using the pin or a sharp pencil in the middle of your large piece of paper or card. And your pinhole camera is ready to go!

You now need to find a suitable place outside to project the eclipse onto. Ideally you want to find a smooth, light surface (concrete is perfect). If you cannot find somewhere like this you can use a second sheet of white paper or card placed on the floor, at least a metre away from your pinhole camera.

Now you are all set! Remember that the eclipse will take place in the morning of the 20th March 2015 and is due to peak at around 9:30 am so make sure you are ready and waiting.

When you are ready you need to stand with your back to the sun and hold your home-made pinhole projector above your shoulder. Make sure that your head is not blocking the hole. If you have this in the right place you should see a perfect circle on the ground. This circle is a projected image of the sun.

As the eclipse progresses you will be able to watch this circle shrink and become a crescent as the shadow of the moon moves across the sun. Try tracing the shape as it changes and experiment with multiple pinholes or a colander.

You’re now set to view the eclipse! But why is this eclipse happening?

What causes a solar eclipse?

Solar eclipses happen when the moon passes directly between the earth and the sun. The moon orbits the earth taking 27 days, 7 hours, 43 minutes and 11.6 seconds to complete one full journey around the planet.

Given this orbit, you might expect that we would get a solar eclipse every month. However due to the path of the moon’s orbit, and the phase of the moon, solar eclipses are actually much less frequent.

File:Eklipsi i plote lunar.JPG

How a solar eclipse occurs CC-BY-SA QHyseni

Half of the moon faces the earth. We can only see the part of the moon that the sun is shining on, the rest of the moon facing us is cast into shadow. Throughout the month the amount of the moon that we can see from earth changes and we get half moons, a full moon and crescent moons. Eclipses only happen during the phase called the new moon. This is where the moon passes between the earth and the sun on its orbit, so there is no sun shining on the side of the moon we can see.

We miss out on a monthly eclipse because the moon’s orbit around earth is tilted at a 5 degree angle to earth’s orbit around the sun. As a result the moon doesn’t always block out the sun. However, every once in a while, the moon’s orbit and the earth’s orbit line up perfectly and it is in these new moon phases that the moon will obscure some or all of the sun, and we get an eclipse.

When is a solar eclipse a total solar eclipse?

The moon’s orbital path is slightly tilted in a squashed circle shape called an ellipse. This ellipse shape means that the distance of the moon from the earth varies during the moon’s orbit. We see this as the moon appearing to change size in our night’s sky; sometimes looking smaller and sometimes looking bigger (not to be confused with the moon illusion).  If the moon is close to the earth when it passes between the Earth and the sun, we will get a total eclipse of the sun. If the moon is further away then we will only get an annular eclipse and we will see a “ring of fire” or annulus around the moon.

What makes this solar eclipse special?

This eclipse is special to us in the UK because we can actually see it! Because the moon is a lot smaller than the sun it will only block out the sun over a certain part of the world. This eclipse will occur only in Europe and parts of Northern Africa. The UK isn’t in the centre of the path the moon’s shadow will take, so we will only see a partial eclipse.

The 20th of March 2015 is also the spring equinox, a day where the sun spends almost equal amount of time above and below the horizon. This means that day and night last for nearly the same amount of time. The March equinox marks the first day of spring in the northern hemisphere, and this year the moon has decided to make this seasonal occasion extra special!

The path of the moon's shadow

The path of the moon’s shadow

When is the next solar eclipse?

If you’d like to see another partial solar eclipse as good as this one, and you don’t want to leave the UK, then put the 12th of August 2026 in your calendar. The next total solar eclipse visible in the UK won’t be until the 23rd of September 2090, so make the most of this eclipse and hope for a cloud free sky!

The Royal Astronomical Society have produced a brilliant Solar Eclipse Leaflet with links to resources and more information.




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Posted in Activity, Exploring Science, Physics, Space
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