The Mars Line in Astrocartography

Born in Honolulu at 7:24 PM, August 4, 1961 (05:24 UTC on the 5th), by his birth certificate, Barack Obama had Mars at 22°34′ Virgo. The site's API returned the lines, the same call the astrocartography map makes with his data, and our script checked them point by point against the Swiss Ephemeris and listed the nearest cities.

How much a rising line bends is set by how far north or south of the sky's equator the planet's zodiac degree lies. Mars at 22°34′ Virgo sits 7°25′ short of 0° Libra, the September equinox point where the zodiac crosses the equator of the sky, and that degree's declination is only 2°56′ north. A point on the equator rises at the same moment of the Earth's turn at every latitude, so Obama's Mars rising line hardly bends: it drifts only 10°13′ east to west over the whole span from 60° S to 60° N, while his Venus line, near the solstice degree, covers 97°17′.

It also means his Mars rising line stays close to a quarter of the globe west of his Mars MC line at every latitude. Read the last column of the table as the share of the Earth's turn that Mars's degree took to climb from the horizon to the meridian at each latitude:

For a reader of the map this is convenient: if you know where a Mars line like this crosses one latitude, you know roughly where it crosses all of them. It is not typical. A Mars in Gemini or Sagittarius, near the solstices, gives rising and setting lines that curve as hard as Venus's do here.

Obama's certificate gives the birth to the minute. Many people know theirs only to the nearest half hour, and his Mars lines show what that uncertainty costs. Had the certificate said 7:54 PM, the Earth would have turned another 7°30′ before the chart was cast, and every one of his lines would sit that far west.

The Mars rising line would leave the Volga and Tabriz behind. It would run instead past Moscow, through southeastern Turkey near Gaziantep and Diyarbakır and northern Syria at Aleppo, and down the Red Sea coast of Arabia past Jeddah and Makkah. The Mars MC line would move off central Honshu onto the meridian of Fukuoka, Kitakyushu and Busan, and the IC line would leave the Brazilian coast for the interior, through Goiânia and Brasília. A reading built on a rounded birth time can therefore describe the wrong cities altogether, which is why the first thing to check is how the time was recorded.

The arithmetic is the same for every planet: four minutes of clock time is about one degree of longitude, so thirty minutes is about seven and a half. Mars's own motion barely changes that, and neither the MC and IC lines nor the curved ones are spared. If your birth time is uncertain, read every line on your map as a band rather than a line, and widen the band by a degree for every four minutes of doubt.

Obama's Mars was 40°01′ east of the Sun, an evening planet low in the west after sunset, and 2.27 AU away, more than twice as far from us as the Sun. It had been moving forward since it stationed direct on February 6, 1961 at 29°59′ Gemini, and its daily motion at the birth was 0°37′. Seen from so far away, its orbital tilt hardly shows: it was 0°43′ north of the ecliptic, so the in mundo lines Jim Lewis drew would sit close to the site's zodiacal ones.

A Mars near opposition is a different case. Then Mars is close to us and its tilt is magnified: in our scan from 1900 to 2050, Mars reached 6°51′ south of the ecliptic on August 14, 2050, 0.374 AU away and opposite the Sun. A birth then would give a Mars whose two kinds of line, zodiacal and in mundo, part by hundreds of kilometers at mid-latitudes, roughly what the Moon's do in Obama's own chart.

How far a Mars line reaches is, as for every planet, a convention. Jim Lewis's handbooks went from a quarter of an inch of map either side (1976) to as much as 700 miles (1982). Using the larger figure, 559 of the site's cities, 24%, come within that distance of at least one Mars line. And as the half-hour example showed, the birth time matters at least as much as the orb.