CHARLOTTE, NC (WBTV) - Many of us already have Spring Fever. You probably heard that Meteorological Spring began March 1st.
But the true first day of Spring doesn't arrive until March 20th, which is based on the earth's orbit around the sun. It occurs when the tilt of the earth is neither toward nor away from the sun. On this day, the sun is directly over the earth's equator which means everyone on earth experiences equal day and equal night, thus the term 'equinox'. Only problem is, it doesn't really work out very well.
Astronomers measure this equal day by referencing the center point of the sun, it's belly button if you will. Using this as the measuring point, indeed, we will have exactly 12 hours between the moment that point rises on the eastern horizon, and touches the western horizon as it sets.
But the rest of us don't measure sunrise/sunset that way. Sunrise is defined as the moment the upper edge of the sun appears on the eastern horizon.
Sunset is defined as the moment the upper edge of the sun disappears below the western horizon. You can see how this adds length to the 'day' and shortens the length of 'night', and by several minutes.
But wait, there is another factor adding even *more* sunlight to our day. Because the sun's light is bent when passing through the atmosphere (refraction), the light rays from the sun are actually bent around the horizon, and you are actually seeing the sun when it is, in reality, below the horizon – much like a mirage. This alone adds another whopping six minutes of sunlight to our day.
So with these factors added in, making our days longer, then what day do we see equal day and night? Usually about four or five days before the Spring Equinox, so this year it's around March 16th.