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    Re: Venus
    From: Fred Hebard
    Date: 2004 May 12, 21:47 -0400

    The solar constant on the surface of the earth is about 1.9 gram
    calories per square cm per minute.  You could proportion this by the
    ratio of the square of the Earth's distance from the sun by that of
    Venus to get an idea of how much hotter Venus would be, assuming an
    Earth-like atmosphere.  I believe if you assumed the Earth is radiating
    as a blackbody at 25 C, this would give you it's rate of heat
    dissipation.  In the absence of core heating, this would have to equal
    the incoming radiation, which you could assume to start with was equal
    to the solar constant multiplied over the earth's cross section.  The
    blackbody Earth would be re-radiating over it's entire surface area.
    My recollection is that core heating is a significant component of the
    Earth's mean temperature, which may be the reason for Venus' lower mean
    temperature, although Venus also is volcanic.
    
    This is a start to rolling your own solution to this problem, and
    perhaps other's who are knowledgeable about actual studies will chime
    in.
    
    Fred
    
    
    On May 12, 2004, at 8:41 PM, Robert Eno wrote:
    
    > This is not exactly a navigation question but given the relationship
    > between navigation and astronomy, I figure it is fair game.
    >
    > I was having a discussion with a fellow regarding global warming and
    > the subject of Venus came up. It is common to hear that were it not
    > for Venus' thick atmosphere the planet would not be so hot and in fact
    > some suggest that it would be within a temperature range that would
    > support life. While I  agree with the greenhouse gas theory of Venus,
    > I indicated to my friend that the idea of Venus supporting life is
    > preposterous; for even without the thick atmosphere its proximity to
    > the sun guarantees daytime temperature that would be far too hot for
    > humans.
    >
    > I think I may be dead wrong in my assumption. A quick search of the
    > net and some of my astronomy textbooks indicates that in the absence
    > of an atmosphere the surface temperature of Venus would be 230 K,
    > which is equal to minus 43 Celsius.  Somehow, despite the evidence
    > before me, this just doesn't seem right. I would have sworn that the
    > temperature would be much highter than that, even without the thick
    > atmsophere.
    >
    > I should know better than to shoot my mouth off on the strength of
    > unproven assumptions.
    >
    > Anyone on the list have a definitive answer to this?
    
    
    

       
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