Where is Here?

Astrolabes for use on Mercury, Venus, Mars ... and even Pluto

Gary James Stilwell MD
astrolabe.sketches@gmail.com
https://astrolabe-sketches.site
May 2024

An astrolabe (Arabic: ألٱَسْطُبالر) is an intricate inclinometer employed by ancient astronomers and navigators to measure the altitude of a celestial body above the Earth’s horizon. The first universal astrolabe was invented by the Islamic scholar Abu Ishaq Ibrahim al-Zarqali (b. 1029). Unlike its predecessors, his 'Tablet of al-Zarqali' projected both the equatorial and ecliptic coordinate systems on a vertical plane that cut the celestial sphere at the solstices, permitting its use at any latitude on Earth.

Al-Zarqali, who originally trained as a metalsmith, is also credited with improving the trigonometric tables, calculating the obliquity of the ecliptic, and mapping a stereographic projection of a sphere on a plane. He stated the orbits of the planets are elliptical, not circular, five centuries before Kepler. Copernicus quoted the works of al-Zarqali in his book ‘On the Revolutions of Heavenly Spheres.’ The crater Arzachel ('The Engraver') on the Moon is named in his honor.

Inspired by al-Zarqali, I sketched construction lines to create astrolabes for use on each of the eight planets plus Pluto, appending his trigonometry calculations with contemporary NASA data and JavaScript. Variation between the digital drawings results from each planet’s unique obliquity to orbit in addition to their distinct rotational and orbital periods.

Mercury

Venus

Earth

Mars

I made the multi-planet astrolabe series during my postgraduate studies at MIT in Dr. Elizabeth Cavicchi’s course EC.090 'Re-create Experiments from History: Inform the Future from the Past.’

My curiosity was sparked by the projection effect, the observational illusion caused by viewing distant objects from a particular perspective. I wondered whether an astrolabe could also provide navigational and temporal orientation on the other planets of our solar system? These sketches affirm the ability of al-Zarqali's ingenious instrument to cross space and time and guide future exploration of our neighbors.

I’m grateful for your interest in viewing my work and invite you to share the sketches with others who possess a passion for historical scientific instruments, astronomical art, and/or even visiting Pluto.