Download stars - science1d

The Wonder And Beauty Of:
STARS
Stars: The View From Earth
 Constellation: a group of stars that (from
Earth) resembles a recognizable form
 Astronomers have officially listed a total of 88
constellations – can you name any?
 e.g.: Ursa Major, Cassiopeia, Orion, Pegasus,
Sagittarius, Ursa Minor
 Asterisms: smaller recognizable star patterns
within a larger constellation
 e.g.: Big Dipper, Little Dipper
 Astronomical phenomenon: any observable
occurrence relating to astronomy
Stars: The View From Earth
 Constellations vary greatly in their distances
from Earth
 They appear to be twinkling because they are
of similar brightness
Quick Lab: Reading Star
Charts
 Use the handout to answer the following questions on your
own.
1. In which constellation is Polaris ( the North Star) located?
2. What planet is shown in the constellation Capricornus?
3. Betelgeuse is a large star located in what constellation?
4. What is the name of the constellation that has three bright
stars in a row?
5. What is the name of the star that seems to form the tail of
the swan-shaped constellation known as Cygnus?
6. Is the star Aldebaran located east or west of Betelgeuse?
7. What is the name of the star cluster located midway
between the constellations of Taurus and Perseus?
8. What large star seems to form the right foot of the
constellation commonly referred to as Orion the Hunter?
Quick Lab: Answers
1. In which constellation is Polaris ( the North Star)
located?

It is located in Ursa Minor or the Little Dipper.
2. What planet is shown in the constellation
Capricornus?

Venus is shown in the constellation Capricornus.
3. Betelgeuse is a large star located in what
constellation?

It is located in the constellation Orion.
4. What is the name of the constellation that has
three bright stars in a row?

Its name is Orion.
Quick Lab: Answers
1. What is the name of the star that seems to form
the tail of the swan-shaped constellation known as
Cygnus?

The name of the star is Deneb.
2. Is the star Aldebaran located east or west of
Betelgeuse?

Aldebaran is located west of Betelgeuse.
3. What is the name of the star cluster located
midway between the constellations of Taurus and
Perseus?

The name of the star cluster is Pleiades.
4. What large star seems to form the right foot of the
constellation commonly referred to as Orion the
Hunter?

Rigel is the large star forming the right foot of Orion.
A Star Is Born
 Life span of stars is VERY LONG
 Stars are formed from a collapsing nebula
 Caused by:
 Gravitational attraction of a nearby star
 Shockwave from an exploding star
 Region with greatest amount of matter starts to draw
material towards it using gravity  star forms here
 Star begins to spin from energy of material coming in
 High pressures build up, heating up atoms, star glows
 Protostar: star in the first stage of formation
A Star Is Born
•Eventually, temperature
rises to millions of degrees
Celsius
•Nuclear reactions starts
•Takes thousands of years
for energy from the core
to reach the star’s outside
•
When this finally happens, the
star begins to shine!!
Life Cycle of Stars
 100 years ago, we knew that different kinds
of stars existed
 We didn’t know that they had a life cycle like us
 How a stars evolves in its lifetime depends on
the mass it had when it was originally formed
 Three general mass categories:
Low mass
2. Medium mass
3. High mass
1.
 Different masses have different lives!!
Low Mass Stars
 Use their nuclear fuel much more slowly
 Can last for 100 billion years
 8X longer than the universe’s age right now!!
 Less gravity and pressures than other stars
 Shine weakly as small red stars called red dwarfs
 Light starts dim and gradually gets dimmer
 Get cooler and turns into a white dwarf
 They collapse under own gravity and burn out
 Most stars in our universe are red dwarfs!!
Medium Mass Stars – Like Our Sun
 Burn nuclear fuel faster than red dwarfs
 Takes about 10 million years to use up their fuel
 For those 10 million years, star is quite stable
 Hydrogen fuel begins to run out
 Star collapses under own gravity like white dwarf
 Collapsing raises temp and pressure again in star
 This causes fusion of helium
 He accumulated at the core of the star
 This reignites the star
 But as core heats up, stars expands quickly into a red giant
 e.g.: Aldebaran
 Eventually, He burns out and star collapses, slowly burning
out like white dwarf
High Mass Stars
 These are more than 10 times the mass of Sun
 Gravity makes nuclear reactions accelerate
 Makes star hotter, brighter, and bluer
 Always will explode
 Hydrogen is used up in less than 7 billion years
 Star collapses like low and medium mass stars
 Compression causes He to fuse
 VERY HIGH temps cause star to expand into a
supergiant
 e.g.: Polaris, Betelgeuse
 When He fuel runs out, collapses again
 Process repeats many times  new elements like Fe are
made
High Mass Stars: What an
Ending!!
 If too much of core is made of Fe, star turns off
 Star collapses one final time
 The collapse is so fast and intense, star heats up
to millions of degrees and EXPLODES (supernova)
 All elements of periodic table were made this way
 Explosion sends these heavy elements to space
 Core that’s left after this goes one of two ways,
depending on the mass of the original star:
Neutron Star
2. Black Hole
1.
Neutron Stars
 Star was between 10 and 40 times Sun’s mass
 Supernova’s explosion is outward and inward
 Atoms at core compress and collapse, forming
neutrons
 When star’s core is just a bunch of neutrons
about 15 km across  neutron star
 Made of the densest material known
Black Holes
 Star was more than 40 times Sun’s mass
 After supernova, star’s core is under so much
gravitational force that nothing can stop its
collapse
 Not even formation of neutrons
 Effect of gravity is so great that space, light,
time, and other things all start to fall to a
SINGLE POINT
 They grow with the more stuff they pull in
Life Cycles of Stars
Hertzsprung-Russell Diagram
 Differences between stars include:
Colour
2. Brightness or Luminosity
3. Surface Temperature
1.
 1919 Ejnar Hertzsprung and Henry Norris
Russell sorted and plotted thousands of
stars according to these characteristics
 One of the most important discoveries in
astronomy in the 20th century
Hertzsprung-Russell Diagram
•Showed very clear
relationships
between star
properties
•Colour: red on
right, blue on left,
yellow in between
•Luminosity:
brightest at top,
dimmest at bottom
• Luminosity of
100 means 100
times brighter
than our sun
•Surface temp:
hottest on left,
coolest on right
Hertzsprung-Russell Diagram
 Patterns based on three star properties
Star data forms a distinct band from top L to bottom R
1.
Called the main sequence  sun is a main sequence star
These stars are thought to be in stable main part of their
life cycle
Stars not along the main sequence are often near the
end of their lives







White = hot
Small  dim
Red = cool
Large  bright