It's time to fall back again.

On Sunday morning the clock strikes 1 a.m. twice as daylight saving time comes to an end again.

Here's what you need to know about daylight saving time and why clocks change twice a year in the United States.

When does summer time end?

Daylight saving time began on March 10th and ends on November 3rd.

Unlike in the spring, when we lose an hour and the clocks skip the 2 a.m. hour entirely, on Sunday we gain an additional hour as the clocks jump from 1:59 a.m. back to 1 a.m

The sun will also set earlier in the US as temperatures continue to cool and we move into the late fall and winter months.

Why is this happening?

According to the U.S. Astronomical Applications Department, the practice, established by the Standard Time Act in 1918, is an attempt to extend daylight hours in summer by delaying sunset by an additional hour.

Daylight saving time, a controversial idea after its introduction, was quickly repealed in 1919 and became a local issue. According to the department, it was re-enacted in the early days of World War II and observed from 1942 to 1945.

After the war, implementation of daylight saving time varied from state to state until the 1966 passage of the Uniform Time Act, which standardized daylight saving time dates but allowed local exceptions if states or localities did not want to participate.

According to the ministry, the standardized start and end dates have changed over the years, but since 2007, daylight saving time begins on the second Sunday in March and ends on the first Sunday in November.

How long does standard time last?

Standard time in the United States will remain in place, as will earlier sunsets and darker evenings, until spring is around the corner and daylight saving time begins again.

In 2025, Daylight Saving Time will begin on Sunday, March 9th and end on Sunday, November 2nd, when it will be time to repeat the process.

Are there states that do not take this into account?

Yes, Hawaii and most of Arizona do not observe daylight saving time and therefore do not change their clocks twice a year, according to the Astronomical Applications Department.

Is the US the only country doing this?

No, according to the ministry, most countries have some kind of “daylight saving time”. In the Northern Hemisphere, most countries that observe daylight saving time are in Europe and North America.

Even though other countries adopt Daylight Saving Time, not all countries do so on the same schedule as the United States

There are also countries in the Southern Hemisphere that observe some form of daylight saving time, but below the equator the seasons are reversed, so the start and end dates of their “summer time” are reversed than ours, according to the ministry.

According to the Pew Research Center, only about a third of all countries observe daylight saving time. About half of all countries once followed the practice but no longer do so.

What efforts have been made to end the practice?

In March 2022, the U.S. Senate passed the Sunshine Protection Act, which would make daylight saving time permanent year-round and usher in the era of time change.

Under the bill, Hawaii and most of Arizona would continue to observe standard time year-round.

But the bill has since stalled in the House of Representatives, meaning the U.S. will continue observing daylight saving time until it is passed in that chamber and then signed by the sitting president.

According to the National Conference of State Legislatures, nearly all states have considered legislation to maintain standard or daylight saving time, and 20 states have passed bills or resolutions to establish year-round daylight saving time in the last six years. However, because federal law does not currently allow year-round daylight saving time, states would have to wait for Congress to pass the law to make the change.

What do health experts say?

Some studies suggest that using daylight saving time year-round could reduce traffic accidents and crime.

But a number of experts are not in favor of permanent daylight saving time. That's because, according to sleep experts, the sun should reach its highest point in the sky at midday, known as solar time.

During standard time, people in the U.S. Central Time Zone are perfectly aligned with solar time, but during daylight saving time they are further away from that clock.

The greater the discrepancy with solar time, the higher the risk of health problems, said Dr. Karin Johnson, a neurology professor at UMass Chan Medical School-Baystate and a board member of Save Standard Time, a nonprofit organization advocating for permanent standard time, reports NBC News in 2022.

Sleep experts prefer clocks switching back and forth over permanent daylight saving time. When people wake up in the dark, hormones like cortisol could be higher, which could make them feel sleepier, says Dr. Kin Yuen, a sleep physician at the University of California, San Francisco and fellow at the American Academy of Sleep Medicine. said in 2022.

Because the sun shines later, people may go to sleep later during daylight saving time, which can delay the body's production of melatonin.

Additionally, a June 2022 study found that people whose clock times were not exactly aligned with the sun had a 22% higher traffic fatality rate than those who lived within 30 minutes of the sun's time.