Properties of Stars
Chapter 25.1
A star is a burning ball of gas…
Our Sun is a Star . . .
Star Characteristics
The color of the star
can be a clue to its
temperature.
The hotter the star the
shorter the wavelength
the star emits.
What color(s) would a
hot/cool star look like?
Bringing Back ROYGVBIV
The shorter the wavelength and the higher the frequency
the more energy…..
Hottest stars:
50,000 K
Coolest
stars:
3,000 K
(Sun’s
surface is
5,800 K)
Star Characteristics
Stellar Brightness
Absolute Magnitude
How bright a star
actually is.
Apparent Magnitude
A star’s brightness as it
appears from Earth.
3 factors affect Apparent
Magnitude:
Size
Temperature
Distance from Earth
Absolute Magnitude may be the same but
Apparent magnitude may differ.
Star Characteristics
Parallax
Basic way to measure
star distance.
Slight shifting of the
apparent position of a
nearby star due to the
rotation of the Earth.
The nearest stars
have the largest
parallax angles.
Star Characteristics
Light-Year
The unit used to
measure stellar
distance.
The distance that light
travels in one year.
9.5 x 1012 kilometers a
year.
180,000 miles per
second.
Hertzsprung Russell Diagram
Shows the relationship between the
absolute magnitude and the temperature
of stars.
Temperature measure in degrees Kelvin
Hertzsprung-Russell Diagram
Luminosity:
Amount of power a star
radiates
(energy per second =
Watts)
Apparent brightness:
Amount of starlight that
reaches Earth
(energy per second per
square meter)
An H-R
diagram
plots the
luminosity
and
Luminosity
temperature
of stars
Temperature
Main-Sequence Star Summary
High Mass:
High Luminosity
Short-Lived
Large Radius
Blue
Low Mass:
Low Luminosity
Long-Lived
Small Radius
Red
Life Cycle of Stars
All stars go through
the same first 3
stages:
1. Nebula
a cloud of gas or dust in
space.
Orion Nebula
Life Cycle of Stars
2. Protostar
A collapsing cloud of gas
and dust not hot enough to
go through nuclear fusion.
Nuclear Fusion
Smaller elements fuse
or combine to form
larger elements.
This can only happen in
conditions that have
extreme amounts of
heat.
Nuclear Fusion
Life Cycle of Stars
3. Main Sequence Stars
A star that is in the main sequence line on a H-R
diagram.
90% of stars fall in this category.
Burn Hydrogen until they burn out.
The larger the starting mass of a star the shorter
life span it has as a main-sequence star.
A yellow star like our sun has a life span of about
10 billion years.
Life Cycle of Stars
4. Red Giant or Red SuperGiant
A Medium Mass star or a Massive star will then go
into this phase.
A large bright star with cooler temperatures.
Life Cycle of Stars
5. Planetary Nebula (Medium Size Stars)
or Supernova Explosion (Massive Stars)
Planetary Nebula – the red giant collapses
and turns into a cloud of gas.
Supernova – the super red giant explodes
and has extreme temperatures that form the
rest of the elements that occur naturally.
Life Cycle of Stars
6. White Dwarf (Medium Size Stars),
Neutron Stars (Massive Stars) or Black Holes
(Extremely Massive Stars)
White Dwarf – extremely small, dense, hot
stars.
Neutron Stars – remnant of a supernova,
extremely dense, composed entirely of
nuetrons
Black Holes – a massive star that has
collapsed to such a small volume that gravity
prevents the escape of anything, including
light.
Life Cycle of Stars
Low Mass Stars
Can stay main Sequence Stars for hundreds
of billions of years.
Then they turn into White Dwarfs
Finally after they cool down they turn into
Black Dwarfs.
Life Cycle of Medium & Massive
Size Stars
Our Star – The Sun
Medium Size Star
Made up of gas
Diameter is about the size of 109 Earth
diameters.
Can divide it into 4 parts
90% hydrogen
10% helium
1. The Solar Interior
Cannot be directly
observed.
2. Photosphere
Radiates most of the sunlight we see.
Visible surface of the Sun.
3. Chromosphere
The first layer of the
solar atmosphere.
Lies directly above
the Photosphere.
4. Corona
The outermost part of the solar
atmosphere.
Very weak and only visible when the
photosphere is covered.
Sun Spots
Dark regions on the photosphere
Appear dark because of their temperature
About 1500 K less than their surrounding
temperature.
Prominences & Solar Flares
Prominences – Ionized gases trapped by
magnetic fields that extend from regions of
intense solar activity.
Solar Flares – brief outbursts that normally
last about an hour and appear as sudden
brightening.
Release a ton of energy – UV, radio and X-
ray
Result in Auroras.