1. The Sun is the Solar System.
We
live on the planet, so we think it's an equal member of the Solar
System. But that couldn't be further from the truth. The reality is
that the mass of the Sun accounts for 99.8% of the mass of the Solar
System. And most of that final 0.2% comes from Jupiter. So the mass of
the Earth is a fraction of a fraction of the mass of the Solar System.
Really, we barely exist.
2. And the Sun is mostly hydrogen and helium.
If
you could take apart the Sun and pile up its different elements, you'd
find that 74% of its mass comes from hydrogen. with 24% helium. The
remaining 2% is includes trace amounts of iron, nickel, oxygen, and all
the other elements we have in the Solar System. In other words, the
Solar System is mostly made of hydrogen.
3. The Sun is pretty bright.
We
know of some amazingly large and bright stars, like Eta Carina and
Betelgeuse. But they're incredibly far away. Our own Sun is a
relatively bright star. If you could take the 50 closest stars within
17 light-years of the Earth, the Sun would be the 4th brightest star in
absolute terms. Not bad at all.
4. The Sun is huge, but tiny.
With
a diameter of 109 times the size the Earth, the Sun makes a really big
sphere. You could fit 1.3 million Earths inside the Sun. Or you could
flatten out 11,990 Earths to cover the surface of the Sun. That's big,
but there are some much bigger stars out there. For example, the
biggest star that we know of would almost reach Saturn if it were
placed inside the Solar System.
5. The Sun is middle aged.
Astronomers
think that the Sun (and the planets) formed from the solar nebula about
4.59 billion years ago. The Sun is in the main sequence stage right
now, slowly using up its hydrogen fuel. But at some point, in about 5
billion years from now, the Sun will enter the red giant phase, where
it swells up to consume the inner planets – including Earth (probably).
It will slough off its outer layers, and then shrink back down to a
relatively tiny white dwarf.
6. The Sun
has layers.
The
Sun looks like a burning ball of fire, but it actually has an internal
structure. The visible surface we can see is called the photosphere,
and heats up to a temperature of about 6,000 degrees Kelvin. Beneath
that is the convective zone, where heat moves slowly from the inner Sun
to the surface, and cooled material falls back down in columns. This
region starts at 70% of the radius of the Sun. Beneath the convection
zone is the radiative zone. In this zone, heat can only travel through
radiation. The core of the Sun extends from the center of the Sun to a
distance of 0.2 solar radii. This is where temperatures reach 13.6
million degrees Kelvin, and molecules of hydrogen are fused into helium.
7. The Sun is heating up, and will kill all life on Earth.
It
feels like the Sun has been around forever, unchanging, but that's not
true. The Sun is actually slowly heating up. It's becoming 10% more
luminous every billion years. In fact, within just a billion years, the
heat from the Sun will be so intense that liquid water won't exist on
the surface of the Earth. Life on Earth as we know it will be gone
forever. Bacteria might still live on underground, but the surface of
the planet will be scorched and uninhabited. It'll take another 7
billion years for the Sun to reach its red giant phase before it
actually expands to the point that it engulfs the Earth and destroys
the entire planet.
8. Different parts of the Sun rotate at different speeds.
Unlike
the planets, the Sun is great big sphere of hydrogen gas. Because of
this, different parts of the Sun rotate at different speeds. You can
see how fast the surface is rotating by tracking the movement of
sunspots across the surface. Regions at the equator take 25 days to
complete one rotation, while features at the poles can take 36 days.
And the inside of the Sun seems to take about 27 days.
9. The outer atmosphere is hotter than the surface.
The
surface of the Sun reaches temperatures of 6,000 Kelvin. But this is
actually much less than the Sun's atmosphere. Above the surface of the
Sun is a region of the atmosphere called the chromosphere, where
temperatures can reach 100,000 K. But that's nothing. There's an even
more distant region called the corona, which extends to a volume even
larger than the Sun itself. Temperatures in the corona can reach 1
million K.
10.
There are spacecraft observing the Sun right now.
The
most famous spacecraft sent to observe the Sun is the Solar and
Heliospheric Observatory, built by NASA and ESA, and launched in
December, 1995. SOHO has been continuously observing the Sun since
then, and sent back countless images. A more recent mission is NASA's
STEREO spacecraft. This was actually two spacecraft, launched in
October 2006. These twin spacecraft were designed to watch the same
activity on the Sun from two different vantage points, to give a 3-D
perspective of the Sun's activity, and allow astronomers to better
predict space weather.