Daylight saving time is ending Sunday. Here's what to know as clocks 'fall back.'

It’s time to fall back again. The clock will strike 1 a.m. twice Sunday as daylight saving time once again comes to an end.

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

The clocks skip the 2 o’clock hour entirely, we will gain an extra hour Sunday, with clocks jumping from 1:59 a.m. back to 1 a.m.

When does daylight saving time end?

The sun will also start setting earlier across the United States as we head into the late fall and winter.

Standard time across the United States will remain, as will earlier sunsets and darker evenings, until spring rolls around and daylight saving time starts once again.

How long does standard time last?

The practice, established by the Standard Time Act in 1918, according to the Astronomical Applications Department of the U.S. Naval Observatory, is an effort to extend the daylight hours we have in the summertime by pushing off sunset an extra hour.

Why do we observe daylight saving time?

According to the Astronomical Applications Department, the standardized start and end dates have been changed throughout the years

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

Which states don’t observe?

The U.S. territories of American Samoa, Guam, Puerto Rico, the U.S. Virgin Islands and the Northern Mariana Islands also observe permanent standard time, according to the National Conference of State Legislatures.