Day One

Ellen and I are assigned the task of building a telescope to measure the size of a crater on the Moon. Unlike other Rough Science series we have been allowed a step-up in technology and they have given us polished mirrors and lenses with which to make the scope. This is great as without them there simply would not be time to make a decent scope and make observations.

Kathy and Iain go off to Meteor Crater in Arizona while Mike is starting to do experiments on projectiles hitting the ground from various heights - their challenge is to work out how big the meteorite that made Meteor Crater would have been.

The first thing Ellen and I have to do is work out the properties of the mirror. It is the mirror that collects the light from the distant object and it is the mirror that, along with the eyepieces, provides the magnification.

The mirror collects light from the distant object and focus it to a point some distance in front of the mirror (this is called the focal length). This is the point where you want the eye to be but unfortunately if you look there, your head obscures the very mirror and light coming in. So what you do is put a small slanting mirror (called the diagonal) a little closer to the mirror. This reflects the light from the mirror allowing the focus to take place at right angles to where it would have been without the mirror, and in a place where you can put your head without blocking any of the light.

In order to make up the telescope we need to hold the mirrors in a frame and the size of this telescope frame is dependant on the focal length of the mirror. So our first job is to take the mirror and work out its focal length.

We did this by taking the mirror outside and arranging it so that it ‘looked’ straight at the Sun. Then we took a long piece of wood and moved it between the front of the mirror until the reflected light shone on the wood. As we moved it further away the reflected light became a bright spot because all the suns energy collected by the mirror was being concentrated. At one place the spot was so small and powerful it burned a hole in the wood - the distance from the front of the mirror to the wood is the focal length of the mirror.

We had a lot of fun playing around with the mirror burning pieces of wood. We had to be very careful when moving the mirror so that no reflected light shone on our faces. This basic experiment got us a focal length of about 1 metre for the mirror. This is an important piece of information because, since the diagonal mirror bends the light away, it means that our telescope will be less than 1m long – we can start making up the frame.

Ellen and I start to make up the woodwork for the telescope, she made up a ‘cell’ - a wooden base with three bolts that holds the mirror in place on the telescope frame and will allow us to position it perfectly in alignment later on.

I make up a simple wooden frame to hold the mirror cell and the various other parts of the scope including the eye piece holder, the diagonal and the fitting / mounting brackets to hold the thing in place. The telescope mount will have to wait.

We both get on very well, Ellen is so excited about both making the telescope and using it for observations, especially as Mars is so close at the moment (it won't be this close for many, many years).

At the end of the day we were able to test the scope out with it lying on the floor propped up with a few pieces of wood and use it to look out onto the scrubby hills of the desert floor. It's beginning to work!

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Content last updated: 19/07/2006