|Exploring The Planets
Galileo Galilei (1564-1642)
from a contemporary portrait in the Dibner Library, National Museum of American History, ©Smithsonian Institution.
"First I prepared a tube of lead at the end of which I fitted two glass lenses, both plain on one side, while on the other side, one was spherically convex and the other concave. Then placing my eye near the concave lens I perceived objects...three times closer and nine times larger than when seen by the naked eye alone."
Early in 1610, Galileo observed four "stars" near Jupiter. The motions of the stars relative to Jupiter led Galileo to the conclusion that they were moons of the giant planet. These moons--Io, Europa, Ganymede, and Callisto--are known today as the Galilean satellites in honor of their discoverer.
The Phases of Venus
To the unaided eye, Venus appears to be just a point of light. Galileo observed Venus through a telescope and found the planet to exhibit phases, as does the Moon.
In these photographs, Venus wanes from nearly full to a thin crescent while more than doubling in apparent size.
Images courtesy of Calvin College Observatory
The Craters of The Moon
Galileo first observed that the face of the Moon is not smooth, but pocked by craters.
Sidereus Nuncius, 1610
Ancient Times &
The Greeks || The Renaissance || Age
of The Telescope || Galileo
Discovering Planets || Planetary Satellites
©2002 National Air and Space Museum