Monday, March 20, 2017

Vernal Equinox 2017

The Skunk Cabbage knows that Spring has arrived.

Today at 6:28 AM EST, Winter officially ended and Spring began in the Northern Hemisphere.  The day that this change occurs is known as the Vernal (Spring) Equinox.  The word equinox comes from the Latin words aequus (equal) and nox (night).  On the Equinox the sun strikes directly on the Equator resulting in approximately equal periods of day and night across the globe.

The Earth rotates around its axis approximately once every 24 hours.  However this axis is tilted at 23.5 degrees from the vertical.  The points on the globe that the axis revolves around are referred to as the North and South Poles.  The axis is always pointed toward the same location in the sky.  The North Pole points toward the "North Star" - Polaris.

At any given time, fifty percent of the earth is in sunlight (Day) and the other fifty percent is in darkness (Night).  However, because the Earth is tilted on its axis sunlight does not always strike the Earth at the same angle.  This means during different seasons different parts of the Earth will receive varying amounts of sunlight and darkness.

As the earth revolves around the sun, sometimes the North Pole is closer to the sun, sometimes the South Pole is closer to the sun.  When the North Pole is at its closest, the sun lights a larger portion of the Northern Hemisphere than it does the Southern Hemisphere.  When this happens, we experience Summer in Mid-Michigan and the Southern Hemisphere experiences Winter.  When the North Pole is at its furthest from the sun, we experience Winter and the Southern Hemisphere experiences Summer.  During our Northern Winter, the sun is striking a a larger portion of the Southern Hemisphere than it is the Northern Hemisphere.

On the Equinox, the poles are essentially perpendicular to the rays of the sun so locations in the northern and southern hemispheres receive equal hours of sunlight and darkness.  Mt. Pleasant is located at 43 degrees 36 minutes north of the equator.  On the equinox, it experiences 12 hours 9 minutes worth of daylight.  A location located at 43 degrees 36 minutes south of the equator will receive approximately the same length of daylight.  The hours of daylight that Mt. Pleasant Experiences will grow until it reaches 15 hours 24 minutes around the Summer Solstice.  Then our hours of sunlight will diminish until on the Winter Solstice we experience only 8 hours 57 minutes of daylight, before increasing again.

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