The Friday Cyclotouriste

a geo-photoblog chronicling my "excursions velo"

Archive for the ‘Seven Sisters’ tag

On the Road……Atop the Bolinas Ridge at Civil Twilight

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This image from my recent ride along the Bolinas Ridge captures the specific time of the evening — civil twilight — when ambient light takes on a lovely bluish hue prized by painters and photographers.

Twilight, broadly speaking, refers to the time between sunset and dusk AND the time between sunrise and dawn (the chart below is a helpful tool for visualizing this).

But twilight (both morning and evening) is divided, more scientifically, into civil, nautical, and astronomical segments based upon the number of degrees the center of the sun is below the horizon (6, 6-to-12, and 12-to-18 degrees respectively).

Evening nautical twilight (nautical dusk) is said to end once sea navigation via the horizon line is no longer possible. Evening astronomical twilight (astronomical dusk) ends once the dimmest celestial objects (e.g. galaxies and nebulae) become properly visible to astronomical observation.

Commentary: in the context of the virtual world of Texting, Tweeting, and Tagging (from which I claim no exception) it feels palpably iconoclastic (if not downright subversive) to patiently witness our solar system’s sun disappearing ever so gently beyond the planet’s watery horizon.


Chart delineating Dusk, Dawn, and Twilight


Featured Comment by Shoeless Joe: “There is a biological connection, too, as the rods and cones in our eyes perceive light differently at twilight. It is called the Purkinje Shift (or Purkinje Effect). Wikipedia has a good article on it. One of the beauties of cycling is that it affords many opportunities to “patiently witness” the world around us in a way that is unique to the sport.”

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November 29th, 2010 at 10:09 pm

On the Road……Fairfax Loop via Mill Valley and Panoramic Hwy

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Bay Area on 12/05/09! Got to love the sunshine. And what a picture postcard vista.

You too can find the spot by clicking on the map link under the photo.

In the background are a few of the storied “seven sisters” — a series of beautiful rolling hills. Some are actually quite steep and not so rolling (see also here and here for a few more images of this stretch). I tend to get distracted by the scenery and want to get off my bike and have a little wine, cheese, dried fruit, or whatever else I’ve stowed in my big, roomy front handlebar bag!

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December 13th, 2009 at 11:26 pm

On the Road……Panoramic Highway-to-Mill Valley

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12/05/09: Current and former New York City Bicycle Club members Tania, John, and Carmen. Tania was in town for a visit. John and Carmen now live in SF. I did my best to keep up with these fast club riders during a very hilly 35-40 mile loop to and from Fairfax via Panoramic Highway and Mill Valley. (Here’s a map of the route.)

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December 11th, 2009 at 8:02 pm

On the Road……The Seven Sisters

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Riding toward the summit of Mt. Tam, I struggled to maintain momentum over the series of seven undulating hills, known as “The Seven Sisters” (scroll down to the bottom of this page for more details on the sisters).

Apparently, 90% of all North American car commercials are filmed along this stretch of roadway. I’ve only seen filming once twice.

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June 15th, 2009 at 7:12 am