Re: [asa] physics questions (surf. brightness)

From: Jim Armstrong <>
Date: Thu Sep 18 2008 - 11:56:31 EDT
Are we perhaps actually speaking of luminance, brightness being a physiological response?  :-)   JimA

George Cooper wrote:

Here is one that may surprise some….


If an astronomer is using a 1 meter (aperture dia.) telescope to observe surface features on Jupiter and is using an eyepiece that yields the best surface brightness, how much larger a telescope (aperture) will she need in order to double the surface brightness (assuming she also uses the appropriate eyepiece for max. brightness)?


[Geoerge wrote] This differs from the previous result by having the square of the sum of the speeds instead of the sum of the squared speeds, and will thus be greater because of the cross term 2vV.


On the balloon problem:  Answers previously given are OK but there's a broader viewpoint - perhaps surprisingly, general relativity.  According to Einstein's equivalence principle, an observer in an accelerated frame can always treat the effects of acceleration as an artificial gravitational field in his/her vicinity.  In an accelerating car this gravity is toward the rear and we all know that balloons go up - opposite to the gravitational field - so in this case it will go forward.


Very nice on both.



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