On this date in 1610, Galileo Galilei first saw Io, Europa, and Callisto. Jan 4 through 15, 1610, Galileo Galilei points his newly developed telescope at the sky and observes craters and mountains on the Moon, moving spots on the Sun, four moons revolving around Jupiter, the phases of Venus, and the almost innumerable stars of the Milky Way. These dates are called by some the most important days in the history of astronomy.

• See what else happened on This Date in Astronomy & Space History.
  
• Learn more about Jupiter and its moons.
  
• On this date in 1998, the Lunar Prospector orbitor launched.
  
• Forum Post of the Day:
  
  Subject: is space exploration a waste of money(?)
  "hey guys i need ur help...
  
  i m debating for the topic that space exploration is not a waste of money.can u guys help me out to support my argument wid some evidences...plzzz"(sic)
  poojason1
• The space explosion reported by CNN in today's headlines relates to Black Holes. Check out these Top Fiction Black Holes Videos.

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• * Spotlight: From the Big Bang to the Big Crunch, follow the history of astronomy and space with this Astronomy & Space Timeline.