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Go to Barrows Hall and take the main elevator (near the east end of the building) to floor 7. Now go across the hall to another elevator which takes you to floor 8. Go to the balcony and walk to the west end. The view is truly spectacular on a clear day. You can see all the campus, the Lawrence Berkeley Labs in the hills to the east, most of the San Francisco Bay, and San Francisco in the distance.

The first effect concerns the cables on the Golden Gate Bridge. The horizontal cables are 35 inches in diameter and you can see them easily from Barrows Hall on a clear day. They are 12 miles away, so what visual angle do they subtend at the retina? The answer is approximately 10 seconds of arc! On a very clear day (and with your specs on), you can also see the vertical cables. They subtend only 2 seconds of arc. To give you some insight on these numbers, an individual foveal photoreceptor subtends about 30 seconds of arc. Thus, a person with good acuity can see features whose width is a fraction of the diameter of a single photoreceptor. (Contributed by Ahna Girshick and Stan Klein.)

The second effect concerns the apparent orientation of the water of the Bay. As one looks out toward the Bridge, most people report that the Bay appears pitched up (as if the water would flow toward Berkeley). It’s not a tsunami. Rather it’s the consequence of the sloping terrain of Berkeley as it meets the Bay. Our brains assume that the flat terrain of Berkeley is horizontal (perpendicular to gravity). The Bay is pitched relative to that terrain, so the brain sees the water as pitched. (Contributed by Cliff Schor and Dhanraj Vishwanath.)

The third effect concerns the pier off the Berkeley Marina. You can see the pier toward the right side of the above photograph. What fraction of the distance to Alcatraz (the island to the left of the Golden Gate Bridge) does the end of the pier appear to be? Most people report that it’s more than half the distance. It’s actually approximately 1/3. This is another example of the compression of perceived distance. Very distant objects (like Alcatraz) appear to be closer than they really are. The curvature of the earth might contribute to this illusion as well. (Contributed by Marty Banks.)

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