Video Field Trip
Stars: Life and Death
1. What happens when stars run out of
fuel?
2. What will happen when to the sun when
it dies?
Properties of Stars
Chapter 25, Section 1
Characteristics of Stars
• Color is a clue to a star’s temperature
• Very hot (30,000 K) stars emit their light in the
blue spectrum, red stars are much cooler, stars
with temperatures between 5000 and 6000 K
appear yellow
• Binary Stars – pairs of stars, pulled together
by gravity, that orbit each other
• Binary stars are used to determine the star
property most difficult to calculate – its mass
• The mass of a body can be calculated if it is
attached by gravity to a partner
Star Temperature
Binary Stars
Concept Check
• What is a binary star system?
Measuring Distance to
Stars
• Parallax is determined by taking a picture of a
star at one time, and another picture six
months later; using the angle between its
apparent shift, astronomers can determine how
far away it is
• The nearest stars have large parallax angles,
while those of distant stars are too small to
calculate
• Light-Year – unit used to express stellar
distance, the distance light travels in one year
(~9.5 trillion kilometers)
• Our closest star (besides the sun), Proxima
Centauri, is about 4.5 light-years away from the
sun
Parallax
Stellar Brightness
• Apparent Magnitude – a star’s brightness as
it appears to Earth
• Three factors control the apparent brightness
of a star as seen from Earth: how big it is, how
hot it is, and how far away it is
• Absolute Magnitude – how bright a star
actually is
• To determine absolute brightness, astronomers
measure how large the star is, what
temperature it is, and what its apparent
brightness would be at 32.5 light-years
Stellar Brightness
Concept Check
• What is the difference between apparent
magnitude and absolute magnitude?
Hertzsprung-Russell Diagram
• A Hertzsprung-Russell diagram shows the
relationship between the absolute magnitude
and temperature of stars
• Main-Sequence Star – This category contains
the majority of stars and runs diagonally from
the upper left to the lower right on the H-R
diagram
• Red Giants – a large, cool star of high
luminosity
• Supergiants – a very large, very bright red
giant star
• Cepheid Variables – A star whose brightness
varies periodically because it expands and
contracts, a type of pulsating star
• Nova – A star that explosively increases its
brightness
Hertzsprung-Russell Diagram
Concept Check
• The H-R diagram shows the relationship
between what two factors?
Interstellar Matter
• Nebulae – clouds of dust and gases in
space
• Emission nebulae consist largely of
hydrogen, they absorb ultraviolet
radiation emitted by nearby stars
• Reflection nebulae merely reflect the light
of nearby stars
• Astronomers like to study nebulae
because stars and planets form from
them
Dark Nebula – Horsehead Nebula
Assignment
• Read Chapter 25 Section 1 (pg. 700-706)
• Do Section 25.1 Assessment #1-7 (pg. 706)