Package travelers book three to nine months ahead for the deep-winter weeks. Photographers watch a solar forecast and move within hours to days, usually regionally rather than internationally.

Underlying both is the solar cycle, which runs over roughly eleven years and is now past its recent maximum, meaning the next several seasons are likely to be quieter than the last few. That is a demand headwind no other row in the catalog has.

The photographers share forecast readings, drive out together to escape cloud and light, hold local knowledge about which fjord or lake is clear when the coast is not, and critique each other's images. The bucket-listers do nothing together, before or after.

Regional aurora alert groups which are unusually active and locally organised, night-photography communities, forecast services checked hourly during a season, and operator client lists. The KP, a substorm, the corona, clear skies as the only thing that matters, the green as distinct from the reds, light pollution, a bust, going out, foreground.