earth-sun distance and heat involved

Hi,
I've a question which has been wandering in my head for a while. Maybe
this is not the right place to ask it, but maybe someone could point
me to a better place.

I'll try to ask it as easy as possible.

According to my calculations, the difference between the longest
distance from earth to the sun and the shorstest one are about 4.8
millions of kilometers.

Why the temperature doesn't drastically change because of this?

If this is because of radiation doesn't being too important this far
from the sun, Where can I find a equation which relates radiation with
distance?

Hope you can help me clear my mind.

Regards,
--
Beto

(Beto) writes:

According to my calculations, the difference between the longest
distance from earth to the sun and the shorstest one are about 4.8
millions of kilometers.

Why the temperature doesn't drastically change because of this?

Because the distance only varies by a few percent.


If this is because of radiation doesn't being too important this far
from the sun,

Uh --- just what _do_ you think heats the Earth, then ??? ,:-I


Where can I find a equation which relates radiation with distance?

Look up "Inverse Square Law." If you halve the distance, you quadruple the
radiant flux. For small changes in distance, the percent change in radiant
flux is twice the percent change in distance. However, this is offset by
the fact that re-radiation to space goes as the _fourth_ power of temperature,
so the percent change in temperature is only 1/4 the percent change in the
incoming radiant flux.

The reason why you don't notice the effect of the Earth's varying distance
from the Sun is that the temperature changes due to axial tilt (AKA "seasons")
are so much larger than the changes due to distance from the Sun. Also, there
are these things called "oceans" that act as huge heat sinks, moderating
changes in temperature.

Nevertheless, the annual change in distance of the Earth from Sun
is a small factor that must indeed be included in climate simulations.


-- Gordon D. Pusch

perl -e '$_ = \n"; s/NO\.//; s/SPAM\.//; print;'

In article ,
Beto wrote:
According to my calculations, the difference between the longest
distance from earth to the sun and the shorstest one are about 4.8
millions of kilometers.

That is at least roughly correct.

Why the temperature doesn't drastically change because of this?

Partly because Earth has a lot of thermal inertia: changes in the amount
of sunlight don't change its temperature quickly.

Partly because in the Northern Hemisphere, where most of the people live,
this trend is opposed to the seasons: Earth is closest to the Sun in
January -- Northern Hemisphere winter -- so the changes due to distance
are hidden by the normal seasonal changes.

If this is because of radiation doesn't being too important this far
from the sun, Where can I find a equation which relates radiation with
distance?

Light intensity varies (to a good approximation) inversely with the
square of distance.
--
MOST launched 1015 EDT 30 June, separated 1046, | Henry Spencer
first ground-station pass 1651, all nominal! |

Henry Spencer wrote:
Beto wrote:
According to my calculations, the difference between the longest
distance from earth to the sun and the shorstest one are about 4.8
millions of kilometers.

That is at least roughly correct.

Why the temperature doesn't drastically change because of this?

Partly because Earth has a lot of thermal inertia: changes in the
amount of sunlight don't change its temperature quickly.

Partly because in the Northern Hemisphere, where most of the people
live, this trend is opposed to the seasons: Earth is closest to the
Sun in January -- Northern Hemisphere winter -- so the changes due
to distance are hidden by the normal seasonal changes.

Also because 4.8 million out of 150 million is really not much
difference. It makes a difference of about 3% in light intensity,
hence of about 0.075% in equilibrium absolute temperature, i.e.
about 2 degrees C, or 3 degrees F.

If this is because of radiation doesn't being too important this
far from the sun, Where can I find a equation which relates
radiation with distance?

Light intensity varies (to a good approximation) inversely with the
square of distance.

And equilibrium temperature varies with the fourth root of light
intensity.

Another way to look at it is: take the fourth root of the proportion
of the sky (including the half below the horizon) taken up by the sun,
and multiply that by the surface temperature of the sun, and you get
what the temperature of the earth ought to be. It won't be quite
right since the earth isn't a perfect black body, but it will be
close. This works for all planets, asteroids, comets, space probes,
etc., so long as nearly all their heat comes from the sun, and so
long as they spend no time in the shade (e.g. of a nearby planet).
--
Keith F. Lynch - - http://keithlynch.net/
I always welcome replies to my e-mail, postings, and web pages, but
unsolicited bulk e-mail (spam) is not acceptable. Please do not send me
HTML, "rich text," or attachments, as all such email is discarded unread.

In article ,
Keith F. Lynch wrote:
Also because 4.8 million out of 150 million is really not much
difference. It makes a difference of about 3% in light intensity...

Remember, it's a square law: a 3% difference in distance turns into about
a 7% difference in light.

(However, Keith is correct to point out that the fourth-root law for
temperature greatly reduces the impact of this.)
--
MOST launched 1015 EDT 30 June, separated 1046, | Henry Spencer
first ground-station pass 1651, all nominal! |

In article , Keith F. Lynch
wrote:

Also because 4.8 million out of 150 million is really not much
difference. It makes a difference of about 3% in light intensity,
hence of about 0.075% in equilibrium absolute temperature, i.e.
about 2 degrees C, or 3 degrees F.

4.8/150 = 3.2% in distance, which causes 6.5% change in intensity by
inverse square, and taking the fourth root of 1+that gives 1.6%
temperature change, or 4 degrees C.

--
David M. Palmer (formerly @clark.net, @ematic.com)