The city of Utqiagvik, in the extreme north of Alasca, began a period of 84 days without nightfall this Sunday (10). The phenomenon, called “Midnight Sun”, will leave the region’s almost 5,000 residents unable to enjoy a traditional sunset until August 2nd. Mesmo Anyone who chooses to sleep only at 4am will need to completely close the curtains to be able to rest in the dark.
Esse annual cycle of uninterrupted clarity occurs exclusively in regions between Círculo Polar Ártico and Polo Norte. The duration varies depending on the specific latitude of each location.
Inclinação from Terra causes permanent light
The Earth’s axis of rotation is not perpendicular to Sol. Ele maintains a tilt of approximately 23.5 degrees — as if the planet were slightly “tilted” to one side. Durante the translational movement (the annual orbit around Sol), this tilt causes alternating hemispheres to receive greater exposure to solar radiation.
Quando is summer on Hemisfério Norte, Polo Norte is tilted towards Sol. Because of this angle, while the Terra rotates around itself daily, the areas above the Círculo Polar Ártico receive continuous lighting 24 hours a day. “It’s as if the top of the planet is always ‘looking’ at Sol, regardless of how much Terra rotates,” explains João Batista Garcia Canalle, astronomer and Olimpíada Brasileira coordinator of Astronomia and Astronáutica.
If the Earth’s axis were perpendicular to the plane of the orbit (forming an angle of 90 degrees), the seasons would not exist. The result would be a balance of light at both poles throughout the year.
Sol horizontal circular Movimento
No Alasca, the star’s trajectory does not follow the common pattern of “rising and falling” on the horizon. Instead, he performs a circular, horizontal movement, as if walking around the city. Esse permanent displacement keeps the region illuminated for weeks.
If Terra were flat, Sol would have to “disappear” when it passed to the other side of the supposed disk. Não there would be different seasons in each region of the planet, and phenomena like this would be impossible.
Why is it cold even when the sun is constant?
An apparent contradiction marks life in Utqiagvik: Sol shines uninterruptedly, but temperatures rarely exceed 0°C. The explanation lies in the obliquity of the sun’s rays.
Nas regions close to Linha of Equador, the sun’s rays reach the surface perpendicularly and directly, concentrating a large amount of energy in a small area. Therefore, these regions are hot.
Nos poles, even during periods of constant light, Sol always remains “low” on the horizon. The light reaches the surface at a steep angle, spreading the heat in a diffuse and less intense way. It’s like shining a flashlight directly against a wall: the circle of light is small and bright. If you tilt the flashlight, the light scatters and weakens. Em Utqiagvik, Sol are present, but the rays arrive “lying down”, without enough force to significantly heat the surface.
The opposite cycle will arrive soon
The residents of Utqiagvik will experience the opposite phenomenon in a few months. Quando or Hemisfério Norte is tilted away from Sol, the city will experience the polar night.
From November onwards, approximately 65 days of total darkness will prevail in the region. Sem solar radiation to heat the atmosphere and soil, temperatures will plummet drastically:
- Mínimas between -25°C and -30°C
- Ausência total natural clarity
- Alterações significant in the sleep and wake patterns of inhabitants
- Maior dependence on artificial lighting in all environments
Esse dual cycle of light and thermal extremes defines the annual experience of life in polar regions, completely shaping the routine, health and culture of the few thousand people who inhabit these remote areas of the planet.