Stars
Distances To The Stars
• Stars are separated by vast
distances.
• Astronomers use units called
light years to measure the
distance of stars
• A light-year is the distance that
light travels in a vacuum in a
year
• Proxima Centauri, is the closest
star to the sun.
Measuring_Distance_in_Space__The_Light_Year
Parallax
• Astronomers have developed various methods of
determining the distance of stars.
• The change in position of an object with respect to a
distant background is called parallax.
• As Earth moves in its orbit, astronomers are able to
observe stars from two different positions.
• Astronomers measure the parallax of nearby stars to
determine their distance from Earth
Properties of Stars
• Astronomers classify stars by
their color, size, and brightness.
Other properties of stars are
chemical composition and
mass.
• Color and Temperature – a
stars color indicates the
temperature of its’ surface.
• The hottest stars appear blue
• The cooler stars appear red
• The spectrum of color in a star
is from blues to greens to
yellows and reds.
The_Color_of_Stars
Brightness
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•
•
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The brightness of a star as viewed
from Earth is dependent on many
factors such as color intensity and
distance.
Apparent Brightness – is the
brightness of a star as it appears
from Earth.
The apparent brightness decreases
as its distance from you increases
Absolute Brightness – is how
bright a star really is. The absolute
brightness is a characteristic of the
star and is not dependent on its
distance from Earth.
Composition
• Each star has its own
spectrum.
• Most stars have a
chemical makeup that
is similar to the sun,
with hydrogen and
helium together
making up to 96 to
99.9 % of a star’s
mass.
How Stars Form
• A nebula is a large cloud of gas
and dust spread out over a large
volume of space.
• Some nebulas are glowing
clouds lit from within by bright
stars.
• A star is formed when a
contacting cloud of gas and dust
becomes so dense and hot that
nuclear fusion begins.
How_Stars_Form
Life Cycles of Stars
• Adult Stars – A star’s mass
determines the star’s place on
the main sequence and how
long it will stay.
• The amount of gas and dust
available when a star forms
determines the mass of each
young star.
• The larger the star the more
energy produce.
• Since blue stars burn brightly,
they use up their fuel quickly
and are short lived.
The_Life_Cycle_of_Stars.asf
The Death of a Star
• The dwindling supply
of fuel in a star’s core
leads to the star’s
death as a white
dwarf, neutron star, or
black hole.
Dying_Stars_and_Conclusion
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Groups of Stars
• Astronomers have determined
that more than half of all stars
are members of star systems.
• There are three basic kinds of
star clusters: open clusters,
associations, and globular
clusters.
• Astronomers classify galaxies
into four main types: spiral,
barred-spiral, elliptical, and
irregular.
Expanding Universe
• The observed red shift in the spectra of galaxies shows that the
universe is expanding.
• Astronomers theorize that the universe came into being in an event
called the big bang.
• Dark matter can only be detected by observing its gravitational effects
on visible matter.
Beyond_the_Milky_Way_and_Back_Into_Time.asf
Spin_Around_the_Solar_System__A__Look_to_the_Stars