Answer 1:
The sun gives off rays of light that travel to the
earth. These light waves have energy and heat
associated with them. This heat is carried through
space with each ray of light, but the further away
from the sun you get, the colder it gets (they
lose energy). That's why Mercury and Venus are
much hotter than Earth (they're closer than
Earth), but mars is much colder. (It's further
away than we are). When you stand outside on a
sunny day, you're feeling the heat being
transferred from the ray of light from the sun.
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Answer 2:
There are several ways that heat can be
transmitted, but in this case we're talking about
light, so it's helpful to talk about radiative
heat, which is transmitted through infrared
radiation that is invisible to our eye.
The sun emits light of many different energies.
A helpful way to classify the energy of the light
is through its wavelength or frequency, which you
may have heard of before. (Just like sound, where
you have low frequency bass and high frequency
treble, light can have many different frequencies,
and these correspond to different energies.) Out
of the many frequencies of light that are emitted
by the sun, we can see only a small fraction, and
we call this visible light. Right outside the
visible spectrum of light, you've also heard of UV
(ultraviolet) light, which causes sunburns, and
there's also IR (infrared) light, which tend to
heat things up because it makes atoms and
molecules vibrate. In a toaster oven, the heater
coils glow red hot, and it heats the toast through
the infrared light that's emitted. In the same
way, the sun emits a lot of light, and some of
this light (UV, visible, IR) is absorbed when it
reaches the Earth. Because no energy can be lost,
the energy contained in the light is transformed
into heat, which warms up the Earth. It's not just
the sun that heats the Earth though. A lot of the
Earth's heat comes from radioactive decay of
elements in the Earth, which releases a lot of
heat.
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