One of the simplest yet trickiest tools in physics: the diffraction grating hand spectroscope. Getting students to read the spectral lines and measure wavelengths opens the door to understanding how we identify elements in stars—by their light.
Unlocking the Colours of the Universe: Using a Spectroscope in the Lab
Light is more than just what we see — it's a code waiting to be cracked. Hidden within every beam of light is a spectrum, a rainbow fingerprint that can tell us what the light is made of, where it came from, and even what elements are present in distant stars. The key to unlocking this secret? A simple but powerful tool: the spectroscope.
What Is a Spectroscope?
A spectroscope is an optical instrument that splits light into its component colours, or wavelengths, allowing us to see the spectrum. This can be continuous, like a rainbow, or broken into distinct coloured lines — known as spectral lines — depending on the source of light.
The most common type used in classrooms and labs is a diffraction grating spectroscope, which uses a fine grid (grating) to diffract, or bend, light into a spectrum. Older models might use a prism instead, but the principle is the same: bend light to reveal its hidden structure.
How Does It Work?
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Light enters the spectroscope through a narrow slit.
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It then passes through a collimating lens which makes the rays parallel.
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The light encounters the diffraction grating (or prism), which separates it into its component wavelengths.
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The resulting spectrum is viewed through an eyepiece or projected onto a screen.
Types of Spectra
When using a spectroscope, you might observe three types of spectra:
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Continuous Spectrum: Produced by incandescent solids or dense gases. Shows all visible colours blended smoothly (like a light bulb).
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Emission Spectrum: Bright lines at specific wavelengths, emitted by excited atoms in a gas (e.g. hydrogen or helium lamps).
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Absorption Spectrum: Dark lines superimposed on a continuous spectrum, where specific wavelengths have been absorbed by a cooler gas (as seen in sunlight).
Using a Spectroscope in the Lab
What You Need:
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A handheld spectroscope (or one connected to a digital sensor)
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Light sources: incandescent bulbs, gas discharge tubes (e.g. hydrogen, helium, sodium), or sunlight
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A darkened room for best results
Steps:
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Align the spectroscope with the light source. For gas tubes, use a holder or clamp.
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Look through the eyepiece to view the spectrum.
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Record observations: note the number, position, and colour of spectral lines.
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Compare with known spectra of elements (charts are widely available).
Safety Tip:
When using gas discharge tubes, always handle with care and switch off when not in use — the tubes can get hot and are fragile.
Applications: From Classroom to Cosmos
Once students master using a spectroscope, they can begin to appreciate its wider applications:
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Identifying elements in unknown gas samples
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Studying flame tests by observing emitted light
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Astronomy: Analysing starlight to determine the chemical composition of stars and galaxies
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Forensics and industry: Detecting substances based on their light emission or absorption
Why It’s Challenging (and Rewarding)
At first, it can be tricky for students to line up the spectroscope correctly and focus on the faint spectral lines. But with practice, they begin to see the patterns — and once they realise they’re looking at the same light patterns astronomers use to identify elements in stars, it becomes magical.
Learning to use a spectroscope combines practical skills, analytical thinking, and a sense of cosmic wonder. It bridges the tiny world of atomic structure with the vastness of the universe — all through the simple act of bending light.
Final Thoughts
The spectroscope is one of those pieces of equipment that looks simple, but unlocks deep truths. Whether used in a school lab or by a professional astronomer, it reminds us that science is often about looking more closely — and sometimes, what looks like a beam of white light is a message from the stars.
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