If you watch me, you know I love sunrises and sunsets although, granted, I see a lot more of the latter given my schedule!
To me, there’s just nothing like beginning or ending the day drenched in the glory of the sun.
Okay, that was a little dramatic. One of my viewers sent the following email, which I think is a pretty good question:
How is sunrise defined? When the sun just breaks the horizon? When 1/2 the sun is at the horizon? When the whole sun has crossed the horizon? Something else? -- Bob O.
For that matter, what defines sunset? The sun about to be gone, almost gone? Gone?
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Talk about a can of worms.
Let’s start with the “official” definition of sunrise and sunset which you already know will be complicated: The timekeeper for the United States, the Naval Observatory, defines sunrise and sunset as the moments when the center of the Sun is physically 50 minutes of arc below the horizon, which is less than the width of your finger held at arm’s length.
Well, just what is 50 minutes of arc? And how big is my finger? Well, there are 0.01666667 degrees in a minute of arc. To convert arc minutes to degrees, you should divide the value by 60. Which is to say that our 50 minutes of arc is about 1 degree, .8333 to be exact. What is one degree? Below is MY palm--if you hold your palm at arms length to the horizon, that is about 10°.
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That leaves a little less than my pinky to be 1°. So our fancy definition means you can see about one Frank-Pinky of the sun when it is rising or setting.
Another less fancy explanation is that the upper limb of the sun can still be seen just before sunset or as the sun comes up. So what is a sun’s limb? Not what you think. The word ‘limb’ comes from the Latin ‘limbus’ which means ‘edge’. Ergo (fancy lawyer term), when you see the sun’s top edge that is when it is rising or setting. Here is a good example of that:
The above looks to be just about a perfect sunrise: the top edge just breaking the horizon.
And then there is the Wikipedia sunset definition: The time of actual sunset is defined in astronomy as two minutes before the upper limb of the Sun disappears below the horizon. This would be an example:
And from Click2pins, Mel caught the perfect two-minutes to go sunset:
Funny, at the end of the day, sunsets are actually an optical illusion anyway as the sun is usually well below the horizon even though we’re actually seeing it. You can read more on that here.
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I guess in the end, sunrises and sunsets really are about the way they make you feel, regardless of when they actually occur.
Our newest meteorologist, Brittany Begley, arrived in town this week, and look what welcomed her:
You can see Brittany this Saturday morning on KPRC2 news!
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I hope this blog answers a few questions for you, Bob O. and, oh, Bob, don’t even get me started on civil, nautical, and astronomical twilights!
Frank
Email me with comments and questions.