Reindeer eyes change colour with the season. They shine gold in summer and deep blue by midwinter, an adaptation to the low, slanting light of 69 degrees north. Vision researchers described the shift in 2013. It is one small measure of how thoroughly Rangifer tarandus belongs to this latitude, and of why reindeer feeding and northern lights evenings hold their audience. Sámi herding on the Tromsø coast follows a rhythm set long before tourism. Families moved semi-domesticated herds from inland winter pastures on the Finnmark plateau to island summer grazing on Kvaløya and Ringvassøya, a migration recorded in tax rolls from the sixteenth century. Lichen, chiefly Cladonia rangiferina, sustained the animals through winter; birch leaf and sedge fattened them through the light months. The lavvu — a portable pole tent — sheltered the herders. Norway now counts roughly 250,000 semi-domesticated reindeer, and herding remains a legally protected Sámi livelihood. A reindeer feeding and northern lights tour sits inside that older economy rather than beside it. The Sámi Parliament, Sámediggi, opened in 1989, and Sámi is co-official across much of northern Troms. Language, joik singing and the duodji craft tradition survived a century of state assimilation policy that ended only in the post-war decades. Camps outside Tromsø now double as small cultural institutions: herders explain antler cycles — reindeer are the one deer species in which females carry antlers — earmark systems that identify ownership, and the economics of a herd. Guides on reindeer feeding and northern lights tours are frequently herders themselves, or their children. The transmission is direct. Visitors receive an account of Arctic land use from the people who hold the grazing rights. Above the camps, the second half of the evening belongs to physics. Tromsø sits beneath the auroral oval, the ring of activity that circles the geomagnetic pole. Charged particles from the solar wind strike atomic oxygen between roughly 100 and 300 kilometres up; excited oxygen releases green light at 557.7 nanometres, the colour most cameras record first. Nitrogen contributes violet and crimson at the fringes. The Tromsø Geophysical Observatory has measured the phenomenon since 1930, and Kristian Birkeland argued for its solar origin from Norwegian mountain stations two decades earlier. Aurora, nordlys in Norwegian, is a winter product here only because summer nights are too bright: the sun does not set at all between late May and late July. From September the sky darkens again, and the coupling of pasture and aurora that defines reindeer feeding and northern lights returns to the coast for another season.