Sunrise

Credit.

My friend Steve wrote to me something that got me a-thinking about the sunrise.

Rereading, I imagined the word "sunrise" with equivocation-quotes around it.

I'll try to explain.

Sunrise is generally understood to mean when the leading limb of the solar disk is first above the horizon. If you live somewhere with mountains to the east, you'll realize that this horizon is strictly theoretical. And notice that web-based calculators for the distance to the horizon based on a billiard-ball earth ask you to enter your height.

But even if you were on a western coast or in Kansas, where the theoretical and actual horizons more nearly coincide, atmospheric refraction causes the limb to be visible before it ought to be compared with strict solar system geometry. At the horizon, refraction bends light nearly to the degree of the angular size of the solar disk itself.

So, except for the mountain problem, agreeing on the moment of sunrise would be easier if we lived on the moon.

I tried to research this business for a while (most of the Wikipedia articles appeared to be excellent), I was soon lost in a morass of conflicts between human intentions versus astronomical fact. It reminded me of the Easter-date business I wrote about here.

I can't understand it all. But on the one hand, there's the history of trying to align solar, lunar and civil calendars, and on the other hand just the elemental fear-of-the-dark question of "When will it be light again?"

Bonus:

The Beatles - Here comes the sun.
About three.