Satellites such as the Kepler have been working overtime to
uncover hundreds of new planets in our galaxy. But how did we
first discover the planets in our local volume of space? Here
are the stories of how astronomers living hundreds of years ago
discovered each planet in our solar system. Photo of the 18th
Century Jantar Mantar observatory in Jaipur, India, by Norman
Koren. The innermost planet in our solar system, Mercury orbits
our sun between just under 70 million and 46 million kilometers.
Ancient astronomers knew of the planet's speed around the sun:
Assyrian astronomers associated it with gods such as Nabu, the
scribe and messenger to the gods, while the Greeks named the
body Mercury, the messenger of the gods. The association is apt:
the planet has a short year of 88 days in all. In 1631,
astronomer Pierre Gassendi first observed Mercury making a
transit across the sun, and just a couple of years later,
another astronomer, Giovanni Zupi discovered phases, indicating
that the planet orbited the sun. O