Spring begins anew Thursday
Wed, 19 Mar 2014 20:46:42 GMT —
In just under 24 hours, you can say goodbye to winter and hello to spring when it arrives at 12:57 p.m.
Now that you know the arrival of the season, how about a little information on how Spring changes the time?
On the first day of Spring and of Fall at all locations on earth, the day is about 12 hours and the night is about 12 hours.
This is formally known as the equinox and the word equinox is derived from the Latin words meaning "equal night."
At the equinoxes, both Spring and Fall, the earth's axis is perpendicular to the rays of the sun, which leads to the sun rising and setting due east and west.
Even though the word equinox implies equal daytime and nighttime, this is not exactly true for two reasons.
The first reason is due to how we define sunrise and sunset.
Sunrise is defined as the moment light becomes visible from the sun's disk when the top of the disk rises above the horizon but the center of the disk is still below the horizon. A good example of this is when at sunrise you see the very edge of the sun peeking over the horizon. This definition gives us a little more daylight than night.
Sunset is defined as the moment the sun's disk is no longer visible, which is again after the center of the sun's disk has already set. Basically this is the moment at sunset that you see the sun sink below the horizon. This also gives us a little more daylight than night. These definitions of sunset and sunrise actually give us a longer "day" period than the "night" period on the equinoxes.
The second reason has to do with refraction of light from the sun in the atmosphere.
Refraction will bend the light from the sun and make it appear higher above the horizon than it actually is.
For people living in the mid-latitudes, like here in the United States, the period of exactly 12-hours of light occurs a few days after the fall equinox and a few days before the Spring equinox.
For a fun side note, nearly every year on one or both of the equinoxes, I hear someone say that at exactly the moment of the equinox and only then, you can balance an egg on its end. Despite the folklore surrounding this idea, egg balancing can be done throughout the year and has no connection to the gravitational force of the moon or sun.