Wednesday, March 5, 2014

Extra Daylight in San Diego County from Lat/Long Differences

A stupid thing I've often wondered about is how much extra time I get based on both east-west differences and north-south differences sensitive to the seasons. This is because often, I find myself descending some trail in the failing crepuscular light, as a result of my failing to plan (and failing to bring a headlamp). "The sun has been setting around X at my house in Hillcrest," I say, "but I'm 10 miles west of there! Surely that shall give me a few more moments of illumination and the sun will set at X plus 90 seconds. Thus am I saved!" By symmetry arguments, trail-running vampires who want to get back to the trailhead before dawn should keep reading.

You should be thankful that my deviance is turned mostly to harmless pursuits.

So: comparing between the very southeasternmost corner of San Diego County just south of the Desert View Tower, and the northwesternmost part just north of San Onofre, there is a 6 to 8 minute difference between sunsets, depending on the time of year. On the first day of summer it's 8 minutes; on the first day of winter it's 6 minutes. The reason I'm not just saying eastern- and westernmost is the north-south difference actually makes a difference of about 120 more seconds at the solstices. So 6 of that 6 to 8 minutes is entirely longitude; i.e., entirely just the time it takes the Earth to turn the width of San Diego County.

Now move along and go about your business.

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