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what's up for february jupiter's moons

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jupiter's largest moons were first seen

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400 years ago in early 1610.

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hello and welcome i'm jane houston jones

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at nasa's jet propulsion laboratory in

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pasadena california

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on the 7th of january 1610 in padua

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italy galileo looked up above the

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constellation orion

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he aimed his telescope at the well-known

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starry wanderer the planet jupiter which

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was near orion that night what he saw

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through his telescope startled him and

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marked the beginning of modern astronomy

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jupiter was not just one object as he

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wrote and drew in his journal

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there are three stars in the heavens

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moving about jupiter as venus and

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galileo's january 7th observation showed

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three stars the one star to the west was

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ganymede and to the east there were two

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objects one was the moon callisto and

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the other was a tight pairing of io and

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europa

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they looked like one object in galileo's

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modest telescopic view

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on january 8 he saw a different lineup

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altogether

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there were three stars on one side of

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the planet

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followed by europa and ganymede

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two cloudy nights and two additional

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observations later on january 13th

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galileo identified a fourth object

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orbiting jupiter the arrangement this

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night turned out to be europa on the

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east and ganymede io and callisto on the

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west

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on january 15 all four stars were seen

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on one side of the planet

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everyone who aims a modest telescope or

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even binoculars at jupiter will see the

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same view that galileo did

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the views of tiny moons orbiting the

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king of the planets will surprise and

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delight all who look up

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jupiter is hard to see in the evening

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sky this month but northern hemisphere

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observers may see jupiter and venus

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close together low on the southwestern

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horizon on valentine's day then it will

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be a few months wait until jupiter

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becomes visible in the morning sky

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by august you can once again view

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jupiter and the four galilean moons

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after dinner or as soon as the sun sets

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and the stars come out

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nasa's galileo mission which ended in

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2003 changed the way we look at our

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solar system it found evidence of

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subsurface salt water on europa ganymede

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and callisto and intense volcanic

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activity on io

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nasa's juno mission will launch in 2011

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on a mission to study jupiter

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and the europa jupiter system mission a

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joint mission of the european space

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agency and nasa is slated to launch in

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2020 it will primarily study jupiter's

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moons europa and ganymede and jupiter's

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magnetosphere

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you can learn all about nasa's missions