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This Globe-Within-a-Globe is Essential to Navigating in Space

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While this may look like a snapshot from an alternate futuristic-history of transparent overlays on mechanical globes, it’s a real moment from our past. This is John Glenn cramming in off-world navigation training just weeks before blasting off from Earth.

In February 1962, John Glenn squeezed in a bit more time with this globe-within-a-globe, a celestial training device illustrating the key coordinates for off-world navigation. It’s also aesthetically excellent, reminiscent of the glass displays and transparently layered information so popular in modern fiction.

To identify points in space, astronauts use an angular coordinate system centred on our home planet. The main components are declination, the space-analogue to latitude, and right ascension, a form of astro-longitude. Declination is degrees north or south of the celestial equator, the projection of our Earthly equator into space. Right ascension is roughly equivalent to longitude, but with a few slightly bizarre twists. Instead of degrees east or west, right ascension is typically measured in hours, minutes, and seconds (where an hour is 15° of apparent sky motion as the Earth rotates). The zero-point of the vernal equinox is only slightly more sensible than longitude’s arbitrary Prime Meridian: it’s the intersection of the ecliptic and celestial equator at the moment of the spring equinox.


One of the original Mercury Seven NASA astronauts, Glenn launched from Cape Canaveral on February 20, 1962. He became the first American astronaut to orbit the planet in his Mercury capsule, Friendship 7. The yaw attitude jet clogged after his first orbit, forcing Glenn to switch from automatic control to a manual electrical fly-by-wire system for the rest of the mission. After three orbits in 4 hours and 56 minutes, Glenn’s capsule splashed down in the Atlantic Ocean near Bermuda.


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