Colour and Temperature of Stars

A lamp connected to a variable resistor demonstrates how the color of light changes with temperature, helping to explain why cooler stars appear red while hotter stars shine white or blue.

1. Connect a lamp in series with a variable resistor and a power supply.
2. Begin with a low current so that the lamp filament glows faint red or orange.
3. Slowly decrease the resistance to increase the current through the lamp.
4. Observe how the filament changes color as it gets hotter, moving from red to yellow to white.
5. Relate these changes to the way star colors correspond to stellar temperatures.

Classroom Demonstrations: Colour and Temperature of Stars - Institute of Physics:

📄 Colour and Temperature of Stars - IOP: https://spark.iop.org/colour-and-temperature-stars

• Use a school theatre or hall with dimmable lights to better observe color changes.
• Compare the lamp with a discharge lamp that can produce blue-white light.
• Photograph the lamp at different brightness levels and discuss “color temperature” in photography.

• Ensure wires and connections are secure to prevent overheating.
• Do not exceed the lamp’s rated voltage or current.
• Keep liquids away from electrical apparatus.

• Why do cooler stars appear red while hotter stars appear white or blue? (Cooler objects emit longer-wavelength light like red; hotter objects emit shorter-wavelength light, including blue.)
• Why does the lamp not reach blue light in this demonstration? (The filament cannot reach the extremely high temperatures needed without burning out.)
• How do photographers use the idea of color temperature? (They adjust for the color of different light sources to capture natural-looking images.)