May to early August is the season. The puffins arrive at Hermaness in late April and leave by mid-August; the cliffs are at their loudest and most populated in June and July. The rare flora at Keen of Hamar peaks in late May and June. Summer daylight is extreme — at midsummer there is no real darkness, only a long blue twilight known locally as the "simmer dim".
Outside the seabird season the island goes quiet. Autumn brings dramatic skies and good chances of seeing the Northern Lights from October onwards. Winter is short days, strong wind, and the possibility of ferries cancelled by storms for a day or two at a time. Spring and autumn are the best time for the aurora; deep winter has the longest dark hours but worse weather odds.