Which way is up? An observation and a few computations.

While listening to some music and meditating tonight, my head did not feel upright. By moving my head from side to side, I figured my neck was straight because it felt as if it were at maximal extension. Still, there was something tugging my head back and to the left. Then I realized my head was pulled, more or less, toward the current position of the moon. I wanted to know if this was completely crazy (my guess: yes, crazy), so I tried a second experiment and then ran some numbers.

I turned to face the opposite direction, and tried to undo my mental moon bias. After several minutes of relaxation, my head felt pulled right and forward -- still toward the moon. The sensation wasn't strong in absolute terms, but I definitely felt like the world had gone slightly sideways and my head was not balanced. Even now, facing a new direction, I still feel a tug (back and right, this time, still toward the moon).

After looking up Newton's law of gravity, as well as a few masses and distances, here are some relative forces that might help us gain some perspective.

Mass 1	Mass 2	Distance	Gravitational attraction
Human head, 5 kg	Earth's Moon, 7.36 E+22 kg	385,000 km	0.16 micronewtons (uN)
Head	Another head	1 m	0.0017 uN
Head	Earth's Sun, 1.99 E+30 kg	1.5 E+8 km	29,480 uN
Head	Earth	3,175 km	49 N

So my head's attraction to the sun should swamp the attraction to the moon. However, it was about 11:30pm when I did this experiment, which (I think) means the sun should be just about directly "underneath" me, pulling my head almost straight through the Earth's center. Since Earth's attraction on my head is about 1690 times stronger than the sun's, I'm unlikely to notice the sun's force in this configuration. So much for the sun, and even accounting for the not-perfect alignment at this hour I think the sun would also be pulling my head to the left in the first experiment.

I don't think I should conclude anything from my numbers. That said, I know my head felt pulled in an odd direction, toward the moon, even after turning around. The sensation is better described as gravity going somewhat sideways, and my head did not feel balanced until I moved it back and left. I am willing to believe that a very aware human can sense small differences in force. Consider that human fingers can sense about one-thousandth of an inch discrepancy between two surfaces (a woodworking estimate I read once), and human ears can detect pressure variations down to one-billionth of an Earth atmosphere.

An ear drum is about 55 square millimeters. One atmosphere is about 0.0103 kg per square millimeter. So one atmosphere of pressure variation on an ear drum exerts a force differential of about 0.57 kg times 9.8 m/s^2, or 5.57 newtons (can I really make that calculation? Help would be appreciated!) One billionth of that is 0.00557 micronewtons, which is roughly 28 times weaker than the force of attraction between my head and the moon. And human hearing is weak compared to other animals.

In Mysore-style Ashtanga Vinyasa yoga practice, the day of a full moon or new moon is observed by resting. One explanation for this tradition is that on these days the moon's gravitational attraction is most opposed to the Earth's attraction (full moon), or most aligned with it (new moon), resulting in undesirable lightness or heaviness. These days are called "moon days". I have not yet accepted this explanation, since the moon's attraction on the preceding or subsequent day would be very similar to the attraction on the moon day. However, I am entirely willing to believe we can detect the gravitational attraction of the moon, which seems reasonable given the calculations I just made. There are other explanations for my particular symptoms tonight, but I won't ignore the moon's attraction in the future.

Besides, I've always been attracted to the moon.

Purisima Creek Redwoods, starting in the north-west corner

Saturday, 14 July 2007 I finally made a longer day-hike in the Purisima Creek Redwoods. Two friends and I followed the 7 mile, 1200-feet-gained circuit suggested in 101 Hikes in Norther California by Matt Heid. We spent about three hours on the hike, including stopping for views and snack. We travelled the circuit anti-clockwise, starting from the Higgins-Purisima parking area (PC05). You reach this parking area by taking 92 West to Half Moon Bay, then head south on US 1 until Verde road. Head as straight as possible on Verde road for a few miles. The parking area is on the right, just as the road takes a very sharp uphill left turn. Though you might see many cars, in our experience the hike is fairly intimate and you have plenty of quiet space.

You start out deep in a heavily wooded valley, and climb slowly along the Purisima Creek Trail. Once you meet the Soda Gulch trail, keep left (it's actually kind of straight) and climb a bit faster. Eventually the towering redwoods give way to a long view across the valley you've just circumnavigated, and the already good hike becomes a great hike.

Just as we started the steep descent on the Harkins Ridge Trail, fog from Half Moon Bay fell over the mountain tops. We slipped underneath this blanket as we made our way through the switchbacks and returned to the parking lot. If you just want a quick, steep hike to a great vista, start from the same parking lot and reverse our route. However, you shouldn't underestimate the beauty and impact of the redwoods on the rest of the hike. Perhaps my favorite sights on this trip were the stands of five to ten redwoods growing together in tight circles.

Stationary walking

I have been studying yoga for little while now, learning about meditation from one friend, and have taken a couple sense-meditation walks with another friend. Sometimes I can combine these practices, and meditate somewhat while walking to and from work.

On good days, my gaze softens and broadens, increasing visual awareness. I might focus on breathing and articulation. I can soften my shoulders, face, and neck. My mind will be quiet and restful, instead of grinding through speculations, concerns, and insecurities. On these days, I am receptive and can listen internally and externally to what is happening now. On these days, the internal and external worlds don't seem so separate.

While an undergraduate, I remember walking up a steep hill with a friend named Lisa. For a second I had a strange sensation of the world moving under my feet, instead of my feet propelling me across the ground. I recently rediscovered this sensation, on a good day. I was still, listening, and my feet pulled the trees, water, and mountains toward me. Galileo might point out that normal walking and this "stationary walking" are fundamentally equivalent, but even so the change of perspective is exciting and enlightening.

In stationary walking, I feel I am moving the world where I want it, instead of climbing over life's obstacles to get where I want to go. With stationary walking I am always at my destination.

Tonight was a good night as I walked home from work. The sun had set, and the tree images were soft or silhouetted. My gaze softened in response, and this time auditory awareness grew beyond visual awareness. My thoughts did not disappear, but they did not distract and my mind rested. I could move my head and smile normally at bicyclists and cars that passed, without losing focus or reducing awareness. I felt no threats, internal or external. I saw whole trees without the tunnel vision of analyzing tree-parts. I was breathing, walking, listening peacefully.

Flight in a North American T-6G

A good friend let me ride along in a North American T-6 G trainer today. It was a fabulous ride. The 600hp 9-cylinder radial engine produces a strong, satisfying wind when you have the cockpit's canopies open. I was fortunate to have some time to try my hand on the stick, and found the plane very easy to handle. I think this was because there was so much power available, keeping you well above stall speed (about 60 knots, if I recall correctly). Everything just felt right about the T-6G, from the sound of the engine to the power and handling.

Two recent hikes: Mount Olympus/North Peak (starting at Mount Diablo), and Purisima Creek Redwoods

Sunday, 1 July 2007 I meant to hike from near the summit of Mount Diablo to Mount Olympus, both in the Diablo Range near Walnut Creek, California. Unfortunately, I missed the North Peak Trail turnoff, and instead hiked up North Peak Road to North Peak. The road is very steep, and at the top are two clusters of Antennas. The view was pretty good, and I realize now that I saw Mount Olympus from there. I also scrambled on top of a small rocky outcrop just north of first antennas, where I found a wonderful gnarled tree, and the largest dragonfly population I've ever seen. At one point, I estimated about 50 dragonfiles no more than 10 meters from me. For some reason, I felt compelled to practice Vrikshasana (tree pose) on top of this rock, which probably wasn't a risk-minimizing choice. It felt great as I imagined my stability extending down through the rock and mountain. For what it is worth, here's a great site for Mount Diablo hikes.

Wednesday, 4 July 2007 I didn't have much time this morning, so I made a quick trip to the Purisima Creek Redwoods preserve. I came up highway 35 ("Skyline Boulevard") from the south, and started from the parking area PCO3A (the south-eastern-most parking area). I only had 45 minutes to walk, but the trees were worth the trip. My goal was to tempt myself to come back for a longer trip in the future, and I succeeded at that. I headed north-ish as I drove away from the parking area, toward highway 92 and Redwood City. I didn't have time to stop and really enjoy the beautiful vistas, but they took my breath away regardless.

csegurus.org down for a while (few days), oops

Due to a server move, the csegurus.org site was down for a few days. In short, I forgot to bring it back up after the server was moved. Oops.