Every March we have two annual observations that are not holidays—one is man made and the other is science/nature. The first is the start of daylight saving time and the other is the beginning of Spring. Grammatically speaking, daylight saving time is correct but the common usage over the years has been daylight savings time.
In the U.S., at 2am on the second Sunday in March we set our clocks forward one hour for the start of daylight saving time—or to put it another way, we lose one hour of sleep. This year, the second Sunday falls on March 12, 2017. And on the first Sunday in November at 2am we reverse that process by setting our clocks back one hour—we get an additional hour of sleep to make up for that hour we lost in March. In 2017, that first Sunday is November 5th.
Standard time—the creation of time zones—was instituted in the U.S. and Canada by the railroads in 1883. Due to the vast width of the two countries stretching thousands of miles from the Atlantic Ocean to the Pacific Ocean, it was necessary to establish some method of standardizing train schedules. However, it was not established in U.S. law until the Act of March 19, 1918. The Act also established daylight saving time which was repealed in 1919 while standard time in time zones remained the law. Daylight saving time was re-established in World War II. The Uniform Time Act of 1966 brought standardization of start and stop dates but allowed for local exemptions from its observance. Since then the official beginning and ending dates have changed several times, the most recent being in 2007.
Those states that have opted for the exemption from daylight saving time are Arizona (except for the Navajo, who do observe daylight saving time on tribal lands), Hawaii, and the overseas territories of American Samoa, Guam, the Northern Mariana Islands, Puerto Rico, and the United States Virgin Islands
There are several states that are split between two time zones. Oregon and Idaho are split between the Mountain and Pacific time zones. Florida, Michigan, Indiana (I think I read somewhere that one of Indiana's time zones observes daylight saving time and the other time zone does not), Kentucky, and Tennessee are split between Eastern and Central time zones. Nebraska, Kansas, Texas, North and South Dakota are divided between Central and Mountain time zones.
At one time, Alaska covered four time zones. That has been changed and Alaska is now in two time zones. More than 98 percent of the state's population are in one of these zones, now called Yukon time, which is one hour earlier than Pacific standard time and four hours earlier than Eastern standard time.
And then there is the other annual observance, the one dictated by science/nature—the vernal equinox.
Equinox translates literally to "equal night."
On March 20, 2017, at precisely 6:29AM eastern daylight time, the sun crosses directly over the Earth's equator. That moment is known as the vernal equinox in the Northern Hemisphere announcing the arrival of spring and the autumnal equinox in the Southern Hemisphere announcing the arrival of fall. A second equinox will occur in September.
The fact that the Earth has distinctive seasons is due to the 23.4 degree tilt of the Earth's axis. The Earth receives more sunlight (longer daylight hours) in the summer and less sunlight (fewer daylight hours) in the winter. The tilt of the axis makes the seasons opposite in the Northern and Southern Hemisphere. At the north pole summer gives six months of daylight while at the same time the south pole is experiencing six months of darkness. The closer you are to the equator, the daily hours of daylight and darkness become more equal.
The fall and spring equinoxes are the only two times during the year when the sun rises due east and sets due west. Modern astronomy aside, people have recognized the astronomical connection to the season changes for thousands of years. The ancients of various civilizations all over the world built structures that illustrate this—temples dedicated to their various gods that modern man recognizes as observatories. Not only the spring and fall equinox days, but also the summer and winter solstice days (most and least daily hours of daylight).
I think it's also interesting to note a connection between the spring equinox and Groundhog Day (another holiday derived from the practices and celebrations of the ancients). If the groundhog sees his shadow on February 2, we have six more weeks of winter. And by "coincidence" that six weeks takes us to within a few days of the spring equinox.
A little bit of equinox trivia: According to folklore, you can stand a raw egg on its end on the equinox. One spring, a few minutes before the vernal equinox, twenty-four almanac editors tested the theory. For a full work day, seventeen out of twenty-four eggs stood up on the large end. Then three days following the equinox, they tried the same test again. And guess what? The results were similar. Perhaps the second test was still too close to the time of the equinox? :)
And there you have it—your science lesson for the day.