Hi everyone,
There is a page on Wikipedia about the Earths thermal loss at
<http://en.wikipedia.org/wiki/Geothermal_gradient>
http://en.wikipedia.org/wiki/Geothermal_gradient that quotes 44.2 TW as the
power of which 30TW is from radioactive decay .
People generate far more heat per kg than either the Earth or the Sun about
100 - 120 W thus around 1 to 2 Watts per Kg.
Therefore if you built the Sun out of people ( ignoring the need for Oxygen
& food plus disposal of waste & CO2) it would be much hotter !
John Murrell
Astronomer Without Portfolio
Website www.JohnMurrell.org.uk
From: altair_b@googlegroups.com [mailto:altair_b@googlegroups.com] On Behalf
Of Roy Easto
Sent: 10 November 2012 10:09
To: altair_b@googlegroups.com
Subject: Re: {Altair_B - 3363} -: Planetary Nebulea - thoughts following
Alan's Lecture
I was thinking more about the insulating effect of the crust being so
relatively thin with high temperatures on one side and black space on the
other. And I liked the picture.
There was an article recently about mass loss/gain from the Earth. The Earth
generates 24TW in energy through radioactive decay. If the Earth has an area
of 4 * pi * (6000000)^2 = 4521 trillion square meters then we would have
around 5mW per square meter? The mass loss for the whole Earth (converted
into energy) would be 24*10^12 / (3*10^8)^2 = 0.2 grams per second. Compared
to the Sun's 4 million tons per second although it does have a mass 330000
times larger than the Earth.
So 4000000/330000/0.0002 = 60000 which is the ratio of heat generated by 1
kg of the Sun compared to 1kg of the Earth (unless I've made a simple
mistake(s) somewhere.
Roy
On 10/11/12 08:58, John Murrell wrote:
Hello Roy,
The difference is the Earth is still generating heat through radioactive
decay - the white dwarf core is all at the same temperature (Isothermal) due
to the de-generate state of the core. As a result the temperatute falls from
.c. 100 M K at the base of the (thin) atmosphere to a few time 10^4 K at the
top. Sounds like good stuff to insulate your house with ! Also it absorbs
all the X-Rays from the core ( assuming degenerate matter at 100M K
generates X-Rays)
Does anyone know what the Earth's surface temperature would be from core
heating only ? I seem to recall the power loss is around a couple of watts
per square meter on average ?
John Murrell
Astronomer Without Portfolio
Website www.JohnMurrell.org.uk
From: altair_b@googlegroups.com [mailto:altair_b@googlegroups.com] On Behalf
Of Roy Easto
Sent: 09 November 2012 23:27
To: altair_b@googlegroups.com
Subject: Re: {Altair_B - 3361} -: Planetary Nebulea - thoughts following
Alan's Lecture
Much like the Earth see attached,
Roy
On 09/11/12 21:58, John Murrell wrote:
In last weeks lecture Alan said the temperature of White Dwarfs range from
around 200k Kelvin to 10k Kelvin. When I thought about it this was rather
odd - the White Dwarf is essentially the core of the star compressed so it
heats up more. The Sun's core burning Hydrogen is at around 15 million
Kelvin. This rises to around 100 million Kelvin when the Helium burns into
Carbon and the outer layers are blown off into the planetary nebula. When
the helium burning stops the core collapses and gets even hotter due to
gravitational energy.
So the question is why is the temperature of the white dwarf only a few
times 10^4 Kelvin rather than over 100 million K ?
The result from looking at various books quite surprised me. The core of the
white dwarf is still at over 100 m Kelvin but the outer ( rather thin)
atmosphere is such a good insulator that the outside ( observable ) surface
is much cooler. As a result of this the core only cools at about 6 Kelvin
per year. Thus takes a long time to cool compared to the life of the
planetary nebula.
Regards
John Murrell
Astronomer Without Portfolio
Website www.JohnMurrell.org.uk
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