Cape Town astrocartography

What Cape Town’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 Cape Town 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 Cape Town, because a degree of longitude here is only about 92 km — 17% 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 33.92°S that means a body within 56.1° of the celestial equator. All ten bodies stay inside that, so every one of the forty lines can pass through Cape Town’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 Cape Town gets about 9 hours 44 minutes of daylight, and at the winter solstice about 14 hours 16 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. Cape Town’s clocks run 46 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 161.6°W, half a world away.