Sunday, January 26, 2014

Owen McKenna's Ten/Ten Rule Of Sunlight

In Tahoe, as with everywhere else in the northern hemisphere, the two darkest months are over.
Like Owen McKenna, I don't like long winter nights. Yes, sitting in front of the fire, reading a good mystery while sipping a glass of wine is great experience on a cold, dark night, and winter gives us that. But I like sunshine, and I like it to be light at least through the entire afternoon.
In Tahoe, the days during the month before and the month after the Winter Solstice (December 21st) each have less than ten hours of daylight. Not good for me. So I'm unhappy to see the approach of November 21st. This last week, exactly two months later, I was relieved to see the sun climbing back into the sky. The sun is once again high enough that we can now enjoy ten months of days that are longer than ten hours.
Welcome to Owen McKenna's Ten/Ten Rule Of Sunlight.  
The 21st day in January is when Tahoe's daylight is once again ten hours
long or longer. It will remain that way until November 21st.
There are multiple websites that allow you to calculate your day length for any latitude and for any day of the year. One I like is Here is the link for Sacramento.  You search by finding the closest major city to you that is a similar latitude, i.e. on a north-south basis. You can pick your month. It will give you sunrise and sunset times, day length, and the altitude in degrees of the sun at noon. (Note that the third hit on my Google search - had wildly inaccurate sunset times for Sacramento - an obvious mistake - so like anything on the internet, you can't always assume accuracy.)
It's fun (really!) to compare day lengths and sun angles for cities farther north or farther south. For example, our friends in Seattle find the sun 9 degrees lower in the sky than we do. And during the last week of January, their day length is still 50 minutes shorter. Ouch! But come the Summer Solstice (June 21st) their day length will be over an hour longer than ours.
You can also see how the amount of change in day length increases as we get closer to the spring and fall equinoxes and decreases as we get closer to the summer and winter solstices.
The bottom line is that Tahoe is south enough to get good winter sun but north enough and high enough to not bake in the summer.
For sun lovers, Tahoe is one of the great climates.

Compared to the more than half of the USA that is north of us,
Tahoe has great, high winter sun.

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