Transcript Slide 1

What is the Sun?
The Sun is a Star, but seen close-up.
The Sun is giant ball of very hot, mostly ionized
hydrogen gas that shines under its own power.
What is the Sun?
The Sun IS NOT an average, yellow star.
Surface Temperature
5800 K
The Sun is White
The Sun produces all the
colors of the rainbow in
roughly equal amounts, which
is white light.
If the Sun were yellow, then
white T-shirts would look
yellow in the mid-day
sunshine.
When you observe the Sun
safely, by projecting its image
through a pinhole camera or a
telescope, you see that it is
white.
Don’t stare directly at the Sun!
The UV radiation can damage your eyes.
The Sun is Above Average
Most stars in the Universe are
small, cool, low-mass dwarfs.
The Sun is larger, hotter, and
more massive than these.
There are stars that are much
larger, very hot, and many times
more massive than the Sun. But
these stars are quite rare
compared to the Sun or the lowmass stars.
The Sun is also not median,
mid-range, or most frequent
(mode) in the measures of size,
temperature, brightness, or
mass.
Properties of the
Sun
Property
Sun
Range for Stars in the Milky Way relative to
the Sun
Radius
696,000 km (109 times Earth’s radius)
1x10-1 – 2x103 (more stars smaller than larger)
Rotation Rate
27 days (equator) to 31 days (poles)
Luminosity
(Power
Output)
3.8 x 1026 watts
4x10-2 – 9x106 (more stars less luminous than
more luminous)
Surface
Temperature
5,800 K (average)
1.5x103 – 3x104 K (more stars cooler than
hotter)
Mass
2 x 1030 kg
8x10-2 – 3x102 (more stars less massive than
more)
Composition
70% Hydrogen, 28% Helium, 2% heavier
elements (by percentage of mass)
Typical for Pop I, Pop II stars are more metal
poor
Age
4.8 billion years of an expected 10 billion year
lifetime
105 – 1010 yrs, More older stars than younger
stars