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Characteristics
of Stars
What is a Star?
• A star is a large
collection of matter
that emits huge
amounts of energy
• The sun is the most
important star to us
as it is at the centre
of our solar system
Distances in Space
• The closest star to our solar system is
Alpha Centauri
• It is 40 trillion km away
• A light year is the distance light travels in
one year (9.46 trillion km)
• Alpha Centauri is 4.3 light years away
Life cycles of Stars
How are these stars different?
Classifying Stars
• Stars are classified
based on:
–
–
–
–
Colour
Temperature
Size
Brightness
Colour/Temperature
• The colours of stars tell us something
about their temperature
• A relatively COOL star glows RED
• A very HOT star glows BLUISH-WHITE or
BLUE
Colour
Temperature Range
(°C)
Example
Blue
25 000 – 50 000
Zeta Orionis
Bluish-White
11 000 – 25 000
Rigel
White
7500 – 11 000
Vega or Sirius
Yellowish- White
6000 – 7500
Polaris
Yellow
5000 – 6000
Sun or Alpha Centauri
Orange
3500 – 5000
Arcturus
Red
2000 – 3500
Betelgeuse
Size
• Stars also range in
size from being
SUPERGIANT to
DWARF.
Brightness of Stars
• Just over 2000 years ago, a Greek
astronomer Hipparchus decided to
classify stars based on their brightness:
– Brightest  First Magnitude
– Faintest  Sixth Magnitude
Two ways to look at magnitude:
• APPARENT
magnitude is the
brightness as it
APPEARS to us
• ABSOLUTE
magnitude is the
actual amount of
light given off by a
star at a standard
distance
Plotting the Properties of Stars
• Astronomers plot the
properties of stars on a
diagram that compares
brightness with surface
temperature and colour.
Constellations
• A constellation is a group of stars that
form a pattern
• We recognize 88 constellations today
• Most familiar constellations are named
after characters in Greek mythology
The Big Dipper
• A part of the
constellation Ursa
Major (big bear)
• Resembles an old
fashioned plow and
the shape of a ladle
The Little Dipper
• Part of the
constellation of Ursa
Minor (little bear)
• Tip of the little
dipper’s handle is
the brightest star,
Polaris (the north
star)
Can you see it?
Bootes
• Has the unmistakable
shape of a kite
• Located by following
the handle of the Big
Dipper
• The brightest star is
Arcturus
• Arcturus is 100x
brighter than the sun
Can you see it?
Cassiopiea
• One of the most
recognizable
shapes among
constellations
• A distinct W, formed
by five main stars
Can you see it?
Orion
• One of the most
distinct features is
his belt made of
three stars
• Two key stars are
Betelgeuse and
Rigel
Can you see it?
Canis Major
• Represents one of
the dogs that
accompanied
Orion the Hunter.
• Dominated by the
lead star Sirius
(popularly known as
the dog star)
Can you see it?
A Map of the Sky
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