Daylight saving time is almost here.

For the past four months, we’ve been on standard time. But overnight Saturday, we’ll turn our clocks ahead one hour at 2 a.m., effectively making it 3 a.m. (So don’t schedule any important meetings at 2:30 a.m., because that time won’t exist Sunday — and is not a great time for a meeting, anyway).

This will come with later sunrises and more sunlight later in the day. The exception will be Arizona, which, save for the Navajo Reservation, remains on daylight standard time all year long. That means they’ll keep the earlier sunsets.

Places that observe the change will remain on daylight time until we switch to standard time and “fall back” on the morning of Nov. 2.

The concept originated in 1784, when Benjamin Franklin proposed it as a joke. He had written a satirical letter to the editor of the Journal of Paris calculating the amount that Parisians could save on candles if they shifted their schedules during the wintertime. They’d revert back to normal schedules in the spring.

It wasn’t until 1966 that daylight saving time laws went into effect nationwide. During the 1940s and ’50s, states, counties and even cities made their own decisions. That proved especially confusing for the transportation industry. The Uniform Time Act of 1966, which was put into practice the following year, established dates during which daylight saving time would take effect each year. States were allowed to opt out — as long as times were consistent statewide.

Nowadays, most of the United States springs forward on the second Sunday in March. There are, however, exceptions: Arizona, Hawaii, American Samoa, Guam, the Northern Mariana Islands, Puerto Rico and the U.S. Virgin Islands. (Arizona is an interesting case: The Navajo Nation, which represents a quarter of the land in Arizona, does spring forward. The rest of Arizona got rid of daylight time in 1968, and is permanently on standard time.)

Beyond the changeup of the clocks, we’re gaining daylight anyway. That’s true every spring. In fact, in the Northern Hemisphere, days lengthen more dramatically in March than during any other time of year.

The effect is most dramatic near the North Pole — hence why the northern U.S. and Canada gain the most sunlight in March. Minneapolis gains nearly 95 minutes of daylight during the month. Boston gains 85 minutes, and Atlanta will gain 62 minutes.

South Florida is closer to the equator, where there’s less variation. Miami will see a 45-minute increase in day length. On the equator itself, every day is the exact same length, with just over 12 hours of daylight.

The sun’s most direct rays will also cross north of the equator into the Northern Hemisphere on March 20, which represents the vernal, or spring, equinox.

Then it’s onward to summer — our days will continue to grow until June 20, 2025, which marks the summer solstice. (The hottest temperatures usually lag by about a month, since the atmosphere takes some time to catch up.)

The annual expansion of the daylight hours in spring — and gradual loss of sunlight in the autumn — comes thanks to Earth’s 23.5-degree tilt on its axis.

Regions near the equator experience the most direct sunlight averaged over the year, which is why the tropics are the warmest. On the equator itself, every 24-hour period is divided into equal parts day and night. That’s why every day is exactly 12 hours long. The same is true about night. Sunrise and sunset times might wobble a few minutes up or down over the course of the year, but the length of daylight will never change.

Near the poles, it’s a different story. Earth’s tilt means that regions in the Arctic or Antarctic can be facing toward — or away — from the sun for months on end. That’s the premise behind the “midnight sun” in Alaska. In Utqiagvik, Alaska — the northernmost town in the United States — the sun doesn’t set between May 11 and Aug. 1. Talk about a long day.

But in the wintertime, Utqiagvik is shrouded in inescapable darkness from Nov. 19 to Jan. 22 each year. Locals call it “polar night,” during which the sun plunges below the horizon around the start of winter and doesn’t emerge until spring approaches.

Day length varies the most at the poles and least at the equator. In between, the annual variability is a bit more moderate. In Chicago, the difference between the shortest and longest day of the year is 6 hours 6 minutes. Closer to the equator in Miami, that difference is 3:14. And during the summer, days are longer in Chicago than in Miami.

How can that be? After all, Miami’s average annual temperature is 27 degrees higher than Chicago’s.

It has to do with sun angle. Every place on Earth gets the same number of hours of daylight if you added them up over a year. But not all sunlight is equal. Closer to the equator, it’s more direct. Near the poles, it comes in at a sharper angle, meaning the same beam of light has to warm a greater stretch of land — and the effective warming is less.

Sun angle is also why we have seasons, the angle of the sun above a given location varying over the course of a year during the Earth’s orbit about the sun. It’s Earth’s 23.5-degree tilt on the axis that causes the sun to appear higher or lower during certain parts of the year.