Transcript Stars - TeacherWeb

Stars
Characteristics of Stars
Star Classification
• Stars are classified
using three main
characteristics:
– Size
– Temperature
– Brightness
Size
• Although stars look to
be the same size from
here on Earth, they can
be many different sizes.
• Neutron Stars are the
smallest. They are made
of the material left
behind after a larger star
explodes; about 20
kilometers in diameter.
Size (cont’d)
• A white dwarf is about
the size of our Earth, but
has as much mass as our
sun. It is made of the
blue-white hot core left
behind from a bigger star
whose outer layers
expanded and drifted out
into space when the star
began to burn out.
– Example: Sirius B
Size (cont’d)
• Our Sun is a mediumsized star.
– Made mostly of
hydrogen at very high
temperatures and
pressures (5,500oC).
– Neither solid, liquid or
gas, it is plasma - all the
atoms have been
stripped of their
electrons and the nuclei
are packed together.
• Example: Our Sun,
Alpha Centauri A
Size (cont’d)
• Very large stars, such as
Aldebaran, Arcturus and
Capella are categorized as
giant stars.
• The largest are called
supergiant stars. If our Sun
were a supergiant, it would
fill our solar system as far
out as Jupiter.
– Examples: Betelgeuse,
Rigel
Temperature
• The temperature of a
star is indicated by
the color it glows.
Type of
Star
O
Color
B
Blue-White
10,000 –
25,000
A
White
7,500 –
10,000
F
Yellow-White
6,000 –
7,500
G
Yellow
5,000 –
6,000
K
Orange
3,500 –
5,000
M
Red
Below
3,500
Blue
Surface
Temp (oC)
Above
25,000
Brightness
• Brightness of a star
depends on its size,
temperature, and its
distance from Earth.
– Apparent magnitude
– Absolute magnitude
Apparent
Magnitude
• A star’s brightness as
seen from Earth.
• Measured with
electronic devices.
• Though our Sun
seems very bright to
us, it is not the
brightest star in the
sky, it is just the one
closest to Earth.
Absolute Magnitude
• The brightness the star
would have if it were at a
standard distance from
Earth.
• Astronomers must find
out the star’s apparent
magnitude and its
distance from Earth then
calculate its absolute
magnitude.
Homework
• Write a “Step-Up-To-Writing” paragraph
using this as your topic sentence: “The three
main characteristics used for classifying stars
are size, temperature and brightness.”
• Your paragraph should include, in addition to
the topic sentence, three detail sentences
each followed by an example sentence and
finished off with a conclusion sentence.