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.