The week is ending bright after a long period of darkness for those in the nation’s northernmost city. The sun will rise in Utqiagvik, Alaska, a community nestled deep in the Arctic Circle, for the first time in 66 days.

There hasn’t been a stitch of sunlight in Utqiagvik since Nov. 18, 2020. The city has been clasped in the grips of “polar night,” which visits regions in the Arctic and Antarctic circles every winter.

In Utqiagvik, polar night lasts more than two months, as the sun will remain beneath the horizon until Friday afternoon local time. That’s when the sun will briefly crest over the horizon for three quarters of an hour, rising at 1:16 p.m. and setting again around 2 p.m.

But after a long period of darkness and gloom, brighter days are ahead once again, for Alaska and the Lower 48 alike. In fact, the days are quickly growing longer everywhere in the northern hemisphere as we steadily approach the spring equinox and inch progressively closer to summer.

What determines day length?

Sunrise and sunset times are governed by the changing seasons, a product of the Earth’s tilt on its axis. As the planet revolves around the sun during its annual orbit, the regions experiencing the greatest quantity of and most direct sunlight change.

During the wintertime, places in the Arctic Circle, like Utqiagvik, can find themselves semi-permanently in the shadow of the Earth, pointed away from the sun. That translates to weeks or months of frigid, unshakable darkness. The opposite is true during the summertime, when Utqiagvik sees two months of constant daylight. That’s why Alaska’s North Slope is commonly referred to as the “land of the midnight sun.”

In most places, the days grow at the greatest rate in March, around the time of the spring equinox, when the sun’s most direct rays shift from the southern hemisphere to the northern. On the equinox, everywhere on Earth experiences a rough balance of day and night — not counting the effects of elevation and altitude.

On March 20, Utqiagvik, Miami, Denver, Sao Paolo in Brazil, Sydney and everywhere in between will all experience a day approximately 12 hours long. The same is true at the North Pole and South Pole.

At the equator, every day year-round is 12 hours long, give or take a few minutes, so there’s no variation in actual day length. But the amount of daylight fluctuates more dramatically as one traverses the mid-latitudes toward the poles.

What the ‘vernal equinox’ in March signifies

The vernal, or spring, equinox marks an inflection point in how quickly the days are growing. For areas outside the Arctic and Antarctic circles, March 20 is the peak of how much sunlight is being added every day.

Right now, for instance, Miami is tacking on a minute of sunlight each day, increasing by up to 91 seconds a day in March. Boston’s days are growing by 1 minute 52 seconds now, with day length swelling 2 minutes 52 seconds per day around the equinox. And in Montreal, the amount of daylight is ticking upward by 2 minutes 10 seconds per day, with jumps of 3 minutes 12 seconds per day coming in March.

The rate of increase slackens thereafter, easing to a peak in June around the summer solstice.

But in the Arctic Circle, like in Utqiagvik, things are a bit different. Daylight climbs from zero in the dead of winter to a full 24 hours in the heart of summer. Since they have more ground to make up, day length skyrockets there. The rate of increase is most dramatic not around the equinox, but rather along the fringes of polar night and polar day.

In Utqiagvik, Saturday will feature 42 minutes more of daylight than Friday. That dwarfs the leaps attained around the equinox of 9 minutes 20 seconds per day.

Regardless of where you are in the northern hemisphere, the days are getting longer, and Friday’s sunrise in Utqiagvik may be a reason to smile. After all, brighter days are finally ahead.

The longest days of the year will arrive in June.