Idaho Skies Transcript for December 20th and 21st

PAUL
Welcome to Idaho Skies for December 20th and 21st. We’re your hosts, Paul...

RACHEL
...and Rachel.

PAUL
It’s the winter solstice on the 21st.

RACHEL
The winter what?

PAUL
Solstice. It means sun standing still.

RACHEL
Oh, you mean the first day of winter.

PAUL
That’s right. On the 21st at 9:28 AM, the sun will appear at its lowest elevation with respect to the fixed stars.

RACHEL
And at that time, it will stand directly overhead over the Tropic of Capricorn.

PAUL
This marks the first day of winter in the northern hemisphere and summer in the southern hemisphere.

RACHEL
So the 21st is the day with the shortest day and longest night for Idahoans.

PAUL
The sun appears to drift north and south across the sky because Earth’s spin axis is tilted relative to its orbital plane around the sun.

RACHEL
Recall that our spin axis is fixed in space; in fact, it always points towards Polaris the Pole Star.

PAUL
So in December, the direction towards Polaris is away from the sun.

RACHEL
But the boundary between Earth’s day and night always remains vertical.

PAUL
Therefore, in December, the Northern hemisphere tilts more into the night making night last several hours longer.

RACHEL
Longer nights means there’s more time for ground to cool and less time to warm up from exposure to daylight.

PAUL
Making it even worse, the angle that the sun shines on the surface is sloped even more.

RACHEL
This means the ground experiences less intense sunlight and therefore doesn’t get warm as fast as it does during the summer months.

PAUL
And as a result, cold winters.

RACHEL
That’s Idaho Skies for the 20th and 21st of December.

PAUL
Be sure to follow us on Twitter @IdahoSkies for this week’s event reminders and sky maps.

For Idaho Skies this is Paul...

RACHEL
...and Rachel.

PAUL
Dark skies and bright stars.