Vernal Equinox 2015

Today is the Vernal Equinox, the first day of spring in the northern hemisphere. The new season officially begins at 22:45 UTC, which is 6:45 pm Eastern Daylight Time.

The astronomical seasons are a product of the tilt of the Earth’s axis – a 23.5° angle – and the movement of the planet around the sun. Today, as spring begins, the Earth’s axis is tilted neither toward nor away from the sun.  This position distributes the sun’s energy equally between the northern and southern hemispheres.

Since the winter solstice in December, the arc of the sun’s daily passage across our sky has been moving northward and daylight hours have been increasing. Today, the sun appears directly overhead at the equator and we have approximately equal hours of day and night. The word “equinox” is derived from Latin and means “equal night”.

As a transitional season, spring is a time when the chill of winter fades away and the warmth of summer gradually returns. The largest increase in average daily temperature, however, usually lags the equinox by a few weeks.

Earth’s solstices and equinoxes. Image Credit: NASA

Earth’s solstices and equinoxes. Image Credit: NASA

The Earth’s axis is tilted neither toward nor away from the sun on the Vernal Equinox. Image Credit: NASA

The Earth’s axis is tilted neither toward nor away from the sun on the Vernal Equinox. Image Credit: NASA

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