Aurora colours explained

Why aurora produces different colours

Charged particles from the solar wind collide with gas molecules in the upper atmosphere. Each gas at each altitude emits a specific wavelength of light when excited. The colour you see depends on which gas was hit and at what altitude the collision happened.

This is the same principle as a neon sign: a sealed tube of gas produces a fixed colour because you are always exciting the same atoms at the same pressure. The atmosphere works like a stack of tubes at different pressures, each producing a different output when energised.

Colour by colour breakdown

Each aurora colour corresponds to a specific gas, altitude range, and physical process. The rarity of each colour tracks with how unusual the conditions required to produce it are.

What colours are visible to the naked eye

Camera sensors are more sensitive to certain wavelengths than the human eye at night. Green (557.7 nm) falls within the range of the rod cells used in scotopic (dark-adapted) vision, so green aurora registers clearly. Red (630 nm) is harder for dark-adapted eyes - most people see faint red displays as pale grey or white until activity is strong enough to make the emission bright.

Blue and violet are also difficult for the naked eye but appear clearly in photographs with appropriate exposure times of 5-15 seconds. A test shot facing north will often show colour the eye cannot detect. This is particularly useful at Kp 3-4, where the display may look faint to you but is clearly green on camera.

During a strong storm (Kp 7+), red aurora becomes clearly visible to the naked eye. The May 2024 G5 storm produced red aurora visible across Spain, Texas, and New Zealand - levels bright enough that even the eye's reduced red sensitivity was overcome.

What aurora colour tells you about Kp

Green aurora can appear at Kp 3-4 from high latitudes. Red at the top of a display usually indicates Kp 5+. A full multi-colour display with visible red and pink requires Kp 6 or higher and typically a genuine geomagnetic storm.

If you can see clearly distinct red above the green, Kp is almost certainly at G2 or above. Pink borders at the base of curtains suggest G3. An overhead display with green, red, and pink all visible simultaneously is consistent with G4-G5 conditions. Colour can serve as a rough on-site activity gauge when you do not have a data connection.

Solar maximum and colour variety

During solar maximum - which spans 2025-2026 for the current cycle - higher energy particle fluxes penetrate deeper into the atmosphere and also excite oxygen at greater heights. This produces more frequent red displays and extends the vertical extent of the aurora visible at any given latitude.

The number of displays increases near solar maximum, but the colour variety is one of the most pronounced changes. Observers at mid-latitudes who have watched aurora for years consistently note that red and pink are more common at cycle peaks. If you have not seen a multi-colour display before, the 2025-2026 window offers better odds than any other period in the next decade.