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View Diary: The Most Misunderstood Concepts in Space Science (413 comments)

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  •  Very lovely! Thanks so much. (7+ / 0-)

    You might want to expand on the ambiguity of "size."  I often see things like "exoplanet is twice the size of Earth" and when you read more closely it turns out that it is twice the diameter of Earth and therefore eight times the volume. What the mass would be would of course depend on density as you already pointed out.



    Is it true? Is it kind? Is it necessary? . . . and respect the dignity of every human being.

    by Wee Mama on Thu Jan 24, 2013 at 06:21:09 PM PST

    •  The size of a ball or sphere refers to diameter. (2+ / 0-)
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      gerrilea, CA wildwoman

      It's just a matter of practicality - humans only care about sizes in order to work with things, such as how many of something you can fit on a shelf.  And so if someone says twice the size of a basketball, they mean its diameter would fit two basketballs inside it - not that its internal volume contains twice the volume of one basketball.  The volume of a sphere mostly only matters when using the interior to store things, such as liquids.  

      And since volume is derivable from diameter, and in fact the former has to be computed from half the latter, it's trivial to care what a planet's volume is.

      Pour yourself into the future.

      by Troubadour on Thu Jan 24, 2013 at 07:03:55 PM PST

      [ Parent ]

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