Rio de Janeiro astrocartography

What Rio de Janeiro’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 Rio de Janeiro 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 Rio de Janeiro, because a degree of longitude here is only about 103 km — 8% 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 22.91°S that means a body within 67.1° of the celestial equator. All ten bodies stay inside that, so every one of the forty lines can pass through Rio de Janeiro’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 Rio de Janeiro gets about 10 hours 36 minutes of daylight, and at the winter solstice about 13 hours 24 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. Rio de Janeiro sits almost exactly on its own zone’s meridian, so midday on the clock and midday by the sun agree to within a few minutes. Any planet standing overhead here has its opposite line running down the far meridian at 136.8°E, half a world away.