Hammerfest divides dramatically into two seasons. In winter (mid-November to late January), the sun does not rise at all — the polar night. This is one of the best places in Norway to see the northern lights, which are most active from October to March. The lights are not guaranteed, but Hammerfest's latitude and relatively low light pollution make it a serious contender. Temperatures typically fall to -10°C to -20°C and the wind can be biting.
In summer (mid-May to late July), the midnight sun means continuous daylight. This transforms the town: boat trips run at all hours, the harbour is active late into the night, and the surrounding hills are lush and walkable. Summer temperatures are mild, typically 10–15°C. King crab safaris run year-round. If you want the full Arctic drama of polar night or midnight sun, plan your visit at the extremes rather than the transitional spring and autumn.