Download 27.1: Characteristics of Stars

27.1: Characteristics of Stars
STAR NOTES: Part 1

What is a Star?
–
A body of gases that gives off energy in the form
of light and heat.
27.1: Characteristics of Stars
Are all stars the same? No
1.
Stars range in diameter from
about 20 km to about 1.4
billion km.
2. The sun is a medium-sized star
with a diameter of about 1,392,000
km.
1. Stars differ in mass.
2. Stars differ in color.
3. Stars differ in composition.
4. Stars differ in
temperature.
5. Stars differ in distance
from the earth.
6. Stars differ in
brightness.
7. Stars differ in motion
How Do Astronomers Determine
Composition and Surface Temperature
of a Star?
The surface temperature of a star tells us
what color it will be.
Surface Temperature of a Star
Red stars are the
coolest stars
with surface
temperatures
less than
3,500 °K
Surface Temperature of a Star
Yellow stars, such as
our Sun, have
surface
temperatures
ranging from 5,000
- 7,500°K
Surface Temperature of a Star
White stars have a
surface temperatures
ranging from 7,500 –
10,000°K
White stars are NOT the
same thing as white
dwarfs! White dwarfs
happen at the end of a
star’s life, and they can
be as hot as 100,000 °K!
Surface Temperature of a Star

Blue stars are the hottest stars with
surface temperatures ranging from
10,000 - 60,000°K.
Size of a Star

The size of a star is based on its diameter and its
mass.

For this class the most important thing to
remember about a star’s size is that the mass of
the star determines how that star will evolve and
eventually die.
–
–
–
The greater the mass of the star, the shorter its lifetime
Low mass stars with an original mass of less than 8 times
the sun (8 solar masses) will become Planetary Nebula.
The remnant state of these stars is a white dwarf.
High mass stars containing more than 8 solar masses will
explode violently as a supernova. The remnant state of
these stars is a neutron star or black hole.
How Do Astronomers Determine Composition
and Surface Temperature of a Star?


Composition is determined by the bright-line
spectra emitted by the star.
A spectrometer is an instrument used to analyze
the bright-line spectra.
–
–
The colors and lines of the spectrum determine what the
star is made of.
There are 3 types of spectra.
How Do Astronomers Determine Composition
and Surface Temperature of a Star?
Continuous
Emission
Absorption
A. Continuous spectra are made by
energy
at all wavelengths
_____________________.
B.
C.
Emission spectra
___________________
are produced by heated
elements
____________________.
Each element has its own
bright-line spectra which acts as its
fingerprint
_________________.
Absorption
spectra
_______________
are produced by
The
absence of bright-line spectra
__________________________________________
__________________________________________
How Do Astronomers Determine Composition
and Surface Temperature of a Star?
How do we determine the elements that are in
a star?
known bright-line spectra of
We compare the ___________________
emission spectra
elements to the ____________________
of
stars.
Hydrogen is the most common element in most stars, and helium is
the second most common.
Why Do Stars Appear to Move to an
Observer on the Earth?

Actual Motion – how stars really move!
This can be measured only with highpowered telescopes and other instruments.

Apparent Motion – how stars look like they
are moving to us on Earth!
(Visible to the unaided eye in a dark sky)

Actual Motion
1.
Rotate (spin) (just like Earth).
Stars _____________
2.
Stars revolve around
___________________
(binary star
other stars
system).
3.
Stars move toward or away
from the Earth
_______________________
(blue or red
shifting).
Apparent Motion
ALL THE TIME
1. The Earth moves _______________.
A.
B.
–
rotates
The Earth _____________________.
revolves around the Sun
The Earth _____________________.
This makes the stars in the sky look like they
are moving, BUT THEY ARE _____
NOT REALLY
MOVING!
The Motion of Stars
–
The rotation of the Earth makes the stars look
westward
like they are moving _________________.
–
The North Star, Polaris, does not appear to move
in the night sky. Other stars seem to circle
Polaris, moving in a westward direction. But,
this movement is due to the Earth’s rotation, not
actual motion…
The Motion of Stars
The revolution of the
Earth around the
Sun makes different
stars visible during
different seasons
_______________.
This is because the
position of the
_________________
Earth changes relative
_________________
_________________
to the Sun
during different
times of the year.
27.1: Characteristics of Stars
STAR NOTES: Part 2
Distance to Stars
1.
Light Years
_______________________
(____):
LY
Distance to stars
A. Units used to measure _________________.
B. __________________
are closer so we use
Planets
______________________________.
Astronomical Units
2.
Astronomical Units
__________________________
(____):
AU
measure distances that are
A. Method used to ________________
closer than ________________.
one light year
27.1: Characteristics of Stars
STAR NOTES: Part 2
Distance to Stars
Light Years
1.
2.
3.
great distances.
Units used because of _______________________
300,000
9.5 trillion km/yr.
Light travels ___________km/s
OR ________
Sun, then Proxima Centauri (4.2 LY)
Closet star: our
______________________________
Name and Describe the Way
Astronomers Measure the
Distance From the Earth to the
Stars
Parallax
 This method is used to measure the
distance of a star from the Earth.
How does Parallax work?
 Take a photograph of certain star
 Wait 6 months and re-photograph the
same star.
 Measure the shift between the two
locations.
The closer a nearby star the greater the shift. This only works for
stars that are closer than 1000 light-years.
The Difference Between Absolute
Magnitude and Apparent Magnitude





Approximately 6000 stars are visible to the unaided eye from
earth
About 3 billion can be seen through ground-based telescopes
Over 1 trillion can be observed from the Hubble Space
Telescope
The visibility of a star depends on its brightness and its
distance from the Earth.
Astronomers use two scales to describe the brightness of a
star: apparent magnitude and absolute magnitude.
Apparent Magnitude
How bright a star appears from Earth.


Positive #s = dimmest stars (dimmest seen
with unaided eye is +6).
Negative #s = bright star (Sun: –26.8).
Absolute Magnitude ****
This is figured out by moving all stars to a distance
32.6 light years from Earth. When they are all at
the same distance then compare how bright they
really are.
Example: The Sun’s apparent magnitude is –26.5, but
absolute magnitude is +5.
Like apparent magnitude, smaller numbers are used for brighter
stars
**** The H-R Diagram uses Absolute Magnitude