Transcript the North Star?

The Cosmos
"We are a way for the Cosmos to
know itself."
Carl Sagan
Star Light, Star Bright
Stars and their Characteristics
Life Cycles of Stars Photos
Video comparison
Stars differ from one another in
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Mass
Age
Composition
Brightness
Size
Surface temperature
Distance from Earth
Our star is
The Sun
A star makes fuel by combining atoms in a process
called…
FUSION
The Sun is 93,000,000 miles away.
• How long does it take for light to reach us
from the sun?
• A) 93,000,000 years
• B) 8 minutes
• C) Practically no time at all
It takes about 8 minutes.
• The next closest star is Proxima
Centauri.
• It takes 4 years for light from this
star to reach us.
• So how far away is this star?
8 LIGHT MINUTES
93 MILLION MILES
150 MILLION KILOMETERS
4 light years
• Light Year
–The distance light travels in one
year
–So a light year is a unit for very,
very, very large distances.
Ancient peoples looked at the stars
at night for entertainment.
“No stars for
you until you
clean your slate!”
Anyway, people have been
observing stars for a long time.
• They named the star patterns or
clusters according to mythic heroes.
• These clusters of stars that appear to
be close together because they are
so far away and that resemble these
figures are called constellations.
More about constellations
• There are 88 that can be seen from
Earth.
• These patterns are not altered for
thousands of years and the change
would be very gradual to us.
• Some constellations can be seen
all year long and some cannot.
Ursa Major
• The Big Dipper
• Also known as the Great Bear
• The two stars farthest from the “handle”
are pointer stars. They point toward the
North Star (Polaris).
http://www.asahi-net.or.jp/~fp6m-kud/uma.gi
Do stars move?
During the day
During the year
Circumpolar
• Describes stars and constellations that are
visible to us in the northern hemisphere all
year long.
• Will Polaris always be the North Star?
Ursa Minor (Little Bear) is the Little
Dipper.
• This is an important constellation because
it contains the North Star or Polaris.
• Polaris gets its name based on the fact
that it is over the North Pole.
• The Earth rotates from west to east so
Polaris stays in roughly a fixed part of the
sky.
Some constellations can only be
seen during certain seasons.
• ORION
• Orion is called the Hunter.
• We only see Orion in the winter.
Lyra is only seen in the summer
and fall night sky.
• Lyra is the harp of the Greek
musician Orpheus.
• Lyra contains the 5th brightest
star in the sky (Vega).
Stars have different amounts of
brightness.
• Apparent Magnitude
–Ptolemy is credited with the first
extensive system of putting a
brightness value with stars
–If a star appears really bright like
the Sun, we say is has a high
apparent magnitude.
Ptolemy – “One mochachino
double carmel vanilla latte,
please.”
“So is a star with a bright apparent
magnitude really that bright?”
All stars have an amount of
luminosity (actual
brightness).
• This depends on a star’s
–Size (bigger is brighter)
–Temperature (hotter is brighter)
Absolute Magnitude
• This is the measure of how bright the
star would be if all stars were at the
same distance
• If a star actually is really bright, no
matter how far away it is, then we say
it has a high absolute magnitude.
Stars vary more in size (volume)
than they do in mass.
• A star’s mass cannot be directly
measured.
• How do astronomers get an idea of
how massive a star might be?
• Gravity. A more massive star will
have a greater gravitational pull.
So to wrap up
• Stars can differ
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Temperature
Size
Mass
Density
Luminosity
Composition
H-R
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What would our Sun be?
Hot or Cold
Bright or Dim? Our sun is a Main Sequence Star
Orion Nebula
Eagle Nebula (w/gas pillars)
Protostar
The Sun (main sequence star)
Red Giant
Red Giant
White dwarf
Supergiant
(Betelgeuse)
supernova
Monocerotis
Neutron star
Black Hole Illustration
Carl Sagan
Cosmos Episode 9
The Lives of the Stars Part 1 of 6
1hr. 11 mins
The Life Cycle of Stars
5 mins