SPECTRAL WORKSHOP OVERVIEW I STEP-BY-STEP GUIDE Equipment List Workshop guides II ADDITIONAL MATERIAL Picture of the lamps, professional spectroscopes and 'DIY' spectroscopes III Larger view of the 'DIY' spectroscopes HANDOUTS & WORKSHEETS Spectra of various gases Solar absorption spectra C. 'Guess the gas' answer sheet D. Extra-solar Planet atmosphere absorption plot www.sepnet.ac.uk 1
I STEP-BY-STEP GUIDE Preparation Before Workshop A1. FULL EQUIPMENT CHECKLIST Laminate showing HST extra-solar planet spectra Scissors (one per student or group) Opaque adhesive tape Card tube (one per student or group) CD (one per student or group) Four gas discharge tubes and power supplies Pocket spectrometers Laminates showing the spectra of different elements and the solar emission spectra A2. OPTIONAL EQUIPMENT Prism Diffraction grating paper Digital camera, video capture equipment and laptop Workshop Guides B1. Safety Notices B2. Introduction to Spectra B3. Making a 'DIY' Spectrometer B4. Using the 'DIY' Spectrometer B5. Applications of Spectrometers B4.1 The Sun B4.2 Extra-solar planets 2 Spectral Workshop KEY WORK TO BE DONE TALKING POINTS
B1. SAFETY NOTICES Do not look directly at the sun, with or without a spectroscope. B2. INTRODUCTION TO SPECTRA Ask if anyone knows what a spectra is, or if anyone has ever seen one. Mention rainbows, and ask if anyone knows how they are formed. Show a spectrum using a prism. Explain that spectra are like the colourful finger-prints of gases each gas has a unique spectral 'finger-print'. A solar spectra shows the finger-print of all the gases in the sun. Examining spectra allows us to see the chemical composition of stars and planets from afar. B3. MAKING A 'DIY' SPECTROMETER A spectrometer is a device for splitting light into it's constituent colours. Using the diagram below as a guide, construct a spectrometer. It is of particular importance that the slit should be 0.1 to 1mm. www.sepnet.ac.uk 3
Tape or card Card tube/box Gap <1mm Gap MUST be parallel to the CD 30O 4cm 7cm B4. USING THE 'DIY' SPECTROMETER Use the 'DIY' spectrometers to look at a light bulb, a fluorescent tube and the sky (a safe solar spectrum). Stress that science is about making observations and recording them. Set up the four gas lamps, and get the students to use their spectrometers (or the professional ones) to guess which gas is in each of the lamps. After 15 minutes or so, reassemble and reveal the answers. B5.1 THE SUN The sun is a collection of many different chemicals giving off light at many different wavelengths, so we see an almost continuous distribution of light. Explain the difference between an emission and an absorption spectra. 4 Spectral Workshop
Show a solar absorption spectra, and ask if the student can identify the element corresponding to the dark lines. These correspond to Helium, which was first discovered on the sun (hence the name from the Greek 'helios'). B5.2 EXTRA-SOLAR PLANETS In the last 15 years or so, telescopes have become powerful enough to observe planets orbiting distant stars. When the planet moves in front of the star, it hides some of the star's light this can be observed with a back-garden telescope as a periodic decrease in the light from the star. Professional telescopes can see what wavelengths are absorbed by the atmospheres of these planets. Ask the students to identify the elements corresponding to a laminate of a HST spectra. The spectra shows light from a planet with a sodium rich atmosphere something very strange for us. We are looking for a planet an atmosphere rich in oxygen, nitrogen and carbon dioxide one that can support life as Earth can. This is how we will first detect life on a distant planet with spectroscopy. www.sepnet.ac.uk 5
II ADDITIONAL MATERIAL Picture of the lamps, professional spectroscopes and 'DIY' spectroscopes: 6 Larger view of the 'DIY' spectroscopes: Spectral Workshop