What the Kp number does not tell you
entry 41
A forecast of Kp 5 sounds promising, but the number is a three-hour planetary average. What actually decides whether the sky lights up overhead is the north–south component of the solar wind's magnetic field, Bz. When it swings south and stays there for twenty minutes or more, the curtains start moving. When it flips north again, a "storm" can fizzle into a faint grey arc that the camera sees better than your eyes.
My rule now: watch the real-time Bz trace, not the headline index. A modest Kp with a steady southward Bz has given me better nights than a big Kp with a field that keeps wobbling.
Cameras see green; eyes see grey
entry 38
Rod cells in the eye are not very sensitive to the 557.7 nm oxygen line, so a faint display often looks like a pale cloud that refuses to move with the wind. A ten-second exposure on a phone will reveal the colour. If the "cloud" turns green on the screen, it is aurora. Brighter displays push past that threshold and the colour becomes obvious without any help.
Settings that keep working
entry 35
| Display | Exposure | ISO | Aperture |
|---|---|---|---|
| Faint arc, no motion | 10–15 s | 1600–3200 | widest |
| Active curtains | 3–6 s | 1600 | widest |
| Fast pulsing / corona | 1–2 s | 3200–6400 | widest |
Focus manually on a bright star and tape the ring. Spare batteries go in an inside pocket — cold drains them in under an hour.
On patience
entry 29
Most of my clear nights have produced nothing at all. The good ones tend to arrive around local midnight, after I have already decided to pack up. I now give every clear night at least until one in the morning.