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Pluto Question 2

By Ken Croswell

October 5, 2006









Image of Pluto and Charon by the Hubble Space Telescope. R. Albrecht (ESA/ESO Space Telescope European Coordinating Facility) and NASA.

Five planets are quite bright in Earth's sky: Mercury, Venus, Mars, Jupiter, and Saturn.

But how many of these planets would still be visible to the naked eye--brighter than apparent magnitude 6.0--if they were as far as Pluto's mean distance from the Sun (39.5 astronomical units, or 3.7 billion miles)?

A. All of them.

B. All but Mercury.

C. Only Jupiter and Saturn, the two largest.

D. None of them.

Click a letter--A, B, C, or D--to find out the answer!

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