Astronomy Thought Of The Day: Green Light


In Roman mythology, every morning the goddess of the dawn would fly across the sky prior to the arrival of the sun.  The name of this goddess was Aurora, which was Latin for dawn or sunrise. 

In my younger days, I would spend part of the summer at a lake in northern Vermont.  Perhaps it was the creaking of the old cottage, built in 1905.  Or maybe it was the gentle lapping of the water against the shoreline.  Either way, I distinctly remember waking up in the middle of the night and gazing out the window at a green hue ebbing through the sky.  On this cool summer day I got my first, and to date only, glance of the Aurora Borealis.

During times of heavy solar activity, the sun will sometimes release bursts of solar winds and magnetic fields, typically as part of solar flares, known as a coronal mass ejection.  Over the next 2 - 3 days, these clouds travel to Earth and eventually may interact with Earth's magnetic field.  The interaction generates currents of charged particles, most notably in the polar regions.  The extra energy in the upper atmosphere will collide with the oxygen and nitrogen atoms and produce the aurora known colloquially as either the Northern or Southern lights depending on what hemisphere you are currently located in.

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