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Astrology from another planet
A birth chart is a map of the sky from the place you were born. Move that place to Mars and the sky changes: the Sun moves to another sign, Earth appears as a blue point of light, and the Ascendant follows the slower rotation of Mars. The Moon stays close to Earth, because seen from Mars the two are never more than a fraction of a degree apart.
The chart is computed with French Ephemeris, the open source ephemeris engine behind FreeAstroAPI, and its space extension. Developers can cast charts from Mars, the Moon or any planet out to Pluto in a few lines of Python.
Questions
How is a birth chart on Mars calculated?
You pick a place on Mars and a moment, given as an Earth date and time or as a sol and local time on Mars. We compute where the Sun, the Moon and the planets appear from that spot at that moment. Earth becomes one of the planets in the chart, and Mars disappears from it because you are standing on it. Houses and the Ascendant follow the rotation of Mars, which turns once every 24 hours 37 minutes.
Why is my Sun sign different on Mars?
From Earth, the Sun sits opposite Earth's position in its orbit. From Mars, it sits opposite Mars's position, and Mars is somewhere else on its own, longer orbit. So the Sun is usually in a different sign. The Moon changes too: seen from Mars it always sits right next to Earth, so on Mars your Moon and Earth share a sign.
What does the native zodiac option change?
By default, signs are measured in the usual tropical zodiac, so Taurus means the same thing as in your Earth chart. The native zodiac instead starts at the spring equinox of Mars itself and is measured along Mars's own orbit, as a Martian astrologer would.
Can I cast the chart of a rover landing?
Yes. Pick one of the mission events, or enter any time and place. Mission timelines usually give the time the landing was confirmed on Earth; tick "Time the signal reached Earth" and we subtract the light travel time, between about 3 and 22 minutes depending on where the planets are. Curiosity's landing, confirmed on Earth at 05:31:45 UTC, comes out at 05:17:57 UTC on Mars, its published touchdown time.
How do I find coordinates on Mars?
Choose a landing site or landmark from the list, or enter a latitude and an east longitude. NASA's Mars Trek map and the USGS Gazetteer of Planetary Nomenclature give the coordinates of any named place. Older maps count longitude west: east longitude is 360 minus the west longitude.
How accurate is it?
The positions come from French Ephemeris, the open source engine behind FreeAstroAPI, using NASA JPL planetary data and the IAU rotation model of Mars. Checked against NASA JPL Horizons for observers on Mars, positions agree within a fraction of an arcsecond. The chart is as accurate as your birth time: a few minutes move the Ascendant by about one degree.
Want your chart from Earth? Use the free birth chart calculator.