Ann: Greenhouse effect on Venus

[Jim Hurley]

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>Message: 13
>Date: Thu, 7 Apr 2005 11:15:13 +1000
>From: David Vaughan <dvk at dvkconsult.com.au>
>Subject: Re: Ann: Greenhouse effect on Venus
>To: use-revolution at lists.runrev.com
>Message-ID: <89a5b6e7bd1bf6743c800dcf73b4cfe4 at dvkconsult.com.au>
>Content-Type: text/plain; charset=US-ASCII; format=flowed
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>snip
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>Jim,
>
>So why is Mars colder than a blackbody planet in its orbit position?
>Just curious.
>
>thanks
>David
>



David,

Because Mars is not black, it will absorb only some on the incident 
solar radiation and reflect it reflects the rest, while the Black 
Body planet absorbs all of the solar radiation and so is hotter. 
(This assumes that Mars does no trapping.)

The tricky thing to understand is why Venus, which only absorbs some 
of the solar radiation, is hotter than a black body which absorbs all 
of the solar radiation.

The answer is that a good absorber is also a good radiator. The black 
body absorbs more heat from the Sun than Venus, but it also radiates 
more of it energy than Venus. Venus is not as good an absorber, but 
it is also a poor radiator because it *traps* the solar radiation 
through the greenhouse effect and that energy which is trapped is not 
radiated.

Hope this explains it.

Jim