Good question! It turns out there are three
different ways that heat can be transfered. The
one you might be most familiar with is
conduction: this is what happens when something
warm and something cold touch and heat passes from
the warm object to the cold object directly
(for example, if you touch something hot or cold,
this is how your hand is able to sense it).
Second, there's convection: in convection,
heat is exchanged by physically mixing two fluids
of different temperatures. For example, if
you put some cold milk into some hot tea or
coffee, the milk warms up and the coffee cools
down as the two liquids mix together.
Finally, there's radiation. This one's a bit
more complicated, but the basic idea is that
every object is constantly radiating away
energy; this is because all objects are made up of
atoms that are constantly jittering around.
These atoms are made up of electrically charged
particles, and these particles emit electric
fields. As they jitter around, these electric
fields jitter as well, and can turn into
electromagnetic radiation (this is actually
what makes up the light you see - it's just waves
in the electromagnetic field! And that's why when
an object gets really hot, it starts to glow red -
its atoms jitter faster and faster until they emit
light). But just as the jittering of atoms in
objects causes them to emit electromagnetic waves,
so too can electromagnetic waves hitting an object
cause its atoms to vibrate faster, increasing its
temperature. For example, the red glow you see
coming from coals in a fire is a form of this
electromagnetic radiation, mostly in the form of
what's called infrared radiation. When you
hold your hands up to a fire, the heat you feel
comes from the infrared radiation hitting your
hands and making the atoms in your hands vibrate
Exactly the same thing happens with the sun and
the earth: the surface of the sun is very hot and
is constantly emitting electromagnetic radiation
(including light and infrared radiation).
These electromagnetic waves don't need a medium to
travel through, so they can just travel through
space from the sun to the earth, and when they
hit the surface of the earth, they heat it up.
That's why the sun feels warm on your skin! Its
infrared radiation is the same as the infrared
radiation you feel coming from a fire.
I hope these help!
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