San Francisco astrocartography

What San Francisco’s position does to a reading

Astrocartography is geometry before it is anything else, so where a city sits changes how it behaves. These are facts about San Francisco rather than about you — they hold whoever is reading.

How close is close, here

Distances here are measured as real ground: one degree of orb is 111 km, the same width everywhere on earth. That matters at San Francisco, because a degree of longitude here is only about 88 km — 21% narrower. Older software that measures overhead lines in longitude will therefore report a wider figure than we do for the same city. Neither is wrong; ours describes a distance you could actually walk.

Every line can reach this latitude

A rising or setting line is a horizon curve, and it exists only where the body actually crosses the horizon. At 37.77°N that means a body within 52.2° of the celestial equator. All ten bodies stay inside that, so every one of the forty lines can pass through San Francisco’s latitude. Nothing here is ruled out by geometry — only by your own chart.

The same geometry, in daylight

The equation behind a rising line is the equation behind sunrise, so you can watch it work. At the summer solstice San Francisco gets about 14 hours 37 minutes of daylight, and at the winter solstice about 9 hours 23 minutes. The further a place sits from the equator, the steeper that swing — and the more slanted its horizon lines run.

The clock against the sun

Overhead and underfoot lines are meridians — they depend on longitude, not on what a clock happens to show. San Francisco’s clocks run 10 minutes ahead of its own sun on standard time, so the instant a planet actually crosses this meridian is not the instant local midday suggests. Any planet standing overhead here has its opposite line running down the far meridian at 57.6°E, half a world away.