Spectroscopy – 2 Ways 2 Science

Science Burrito sneaks into your home once more to leave science all over the place like some kind of educational Santa Claus. This time, I thought I’d show you all a bit of what I do for a living.

I am a spectroscopist. That sounds super fancy. I am not super fancy. Maybe I’m a little fancy, but that’s not really important right now. All this word means is that I use light to find out about stuff. Light is really awesome because it can tell us so much about what things are made of and how they work. We can take the light from stars and split that light into a spectrum. That means we take all the different colours of light that come from a star and separate them into individual colours. By looking at what colours are present, and often more importantly, what colours are absent, we can see what the star is made of, or what the light that reaches us has passed through on the way.

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I’ve shown you in previous blog how light can split up by prisms and water and even the atmosphere. There is another way of producing a spectrum through. You can use a grating. This is pretty much just what it sounds like. A grating is a piece of reflective material that is made of lots and lots of lines. But the lines of the grating, to split light up, have to be very, very small (usually hundreds or thousands of lines in every millimetre).

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What you might not realise if you are surrounded by gratings like this every day. A CD or a DVD works by a laser following a track around the disc. This track is very, very small and so the CD acts as a grating. Put a disc up to the light, and you’ll see the different colours appear.

That’s great, but we can be smarter than that. Let’s make our own spectrometer. We can do this two ways. The easy way, and the not quite as easy but still pretty easy way. We’ll look at the second way first.

You’ll need, a CD which you are willing to destroy (DVD’s don’t work as well, so make sure it’s a CD), a box, a toilet roll tube, some scissors, a knife, maybe some tape, and not much else.

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First, you need to make sure your box is sealed all the way around so no light can get in.

Next, use your knife to cut a slit in one side of the box about an inch down. BEWARE! Knives are sharp, this is definitely responsible adult time.

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Next, use your scissors or knife (CONTINUE TO BEWARE and seek assistance from your domesticated responsible adult) to cut a slot for the CD to go in. This needs to be opposite the slit and at a fairly steep angle. Copy and paste the figure below, print it out, and use that as a guide to your cut.

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Now, make a hole to look trough.

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Next, you’ll want to break the CD apart so it fits nicely inside the box. The best way is to score the CD where you want it to break, nice and deep to make sure it breaks right. AGAIN, BEWARE, the CD edges will be sharp. Use tape to round them off.

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Finally, make a viewport by taping the toilet roll tube to the hole over the CD. Now just hold your box, slit side first, up to the light and see the colours on the CD.

The second, even easy way only needs the rest of the CD, the scissors or knife, the tape and your phone.

Use the scissors or knife to scratch the sliver coating off the disc, or, more safely, you’ll probably be able to use you thumb nail. The lines that make the grating are still there on the plastic! Now, tape off the corners and tape the transparent bit of CD over your phone’s camera lens. When you point the phone near lights with the camera on, you should see the light split up into its different colours.

You’ll notice that some lights, like LEDs, make all the colours, but other lights, like fluorescent tubes or energy saving bulbs, have gaps in the spectrum where there is no light. That’s because of the different ways those bulbs produce light.

White LEDs tend to layer different chemicals to merge together a lot of different colours so there aren’t any gaps in the spectrum.

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In energy saving bulbs, a lot of the light comes from exciting mercury with electrical energy. It gets rid of the electrical energy by emitting light, but because it is single atoms of mercury that do this, it is lost at very specific colours instead of a whole range of colours.

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An orange flame shows a bit less blue in its spectrum and a bit more red.

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You can do this with all sorts of other lights too, like street lights or car lights (but don’t wonder into the road!) or Christmas lights (but don’t… actually this one is probably fine, unless they’re on the roof or something, don’t go on the roof!).

And now you’ve done what astronomers do when they study stars millions of miles away. Pretty neat.

 


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