Why Aurora Colours Change

Open on a northern night sky where one broad auroral curtain visibly shifts from green to red, blue and violet. Ask what changes in the atmosphere when the colour changes.

• Focus attention on a single auroral display
• Introduce colour as a clue rather than a decorative effect
• Frame the investigation around particles, gases and height

Ask the learner to choose the main reason an aurora can show multiple colours in one display.

• Commit to one explanatory hypothesis
• Distinguish gas-and-altitude effects from camera or weather effects

Move glowing particles through a layered atmosphere and compare the light produced when they excite oxygen or nitrogen at different altitudes.

• Change the gas and altitude
• Observe the resulting visible colour
• Compare matching emissions from the same gas at different heights

Explain that energetic charged particles transfer energy to atmospheric gases. The gas identity and the altitude—which affects collision conditions and energy—determine which wavelengths are emitted.

• Excited atoms and molecules release energy as light
• Oxygen commonly produces green light at lower auroral altitude
• Oxygen can produce rarer red light at greater altitude
• Nitrogen contributes blue and violet emissions

Present an altitude comparison: green oxygen lower in the display, red oxygen higher up, and blue-violet nitrogen especially near the lower edge. Emphasise that this is a pattern, not a universal rigid boundary.

• Read colour together with altitude
• Separate green oxygen from higher red oxygen
• Identify nitrogen as a source of blue and violet light

Explain that the simple colour-to-height map is an approximation. Rare red auroras can extend unusually low, strong solar activity can excite different layers, and cameras may exaggerate colours beyond what the eye perceives.

• Colour-altitude patterns are typical rather than absolute
• Red auroras can sometimes appear lower than expected
• Camera settings can change apparent auroral colour

Present a changed situation with mixed green, blue-violet and red regions at differing heights. The learner selects the most consistent gas-and-altitude explanation for each region.

• Apply the gas-and-altitude idea to unfamiliar colour zones
• Match green, blue-violet and red to likely sources
• Recognise that multiple gases can glow in one aurora

Return to the opening curtain and answer directly: the aurora does not change colour because the particles themselves are painted differently. Different gases at different heights and energies emit different wavelengths, allowing one aurora to display several colours at once.

• Directly answer the driving question
• Identify oxygen with green and red
• Identify nitrogen with blue and violet
• Resolve the tension between a single aurora and multiple colours