1. The Wonder And Beauty Of:
stars

2. 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

3. Stars: The View From Earth
Constellations vary greatly in their distances from Earth
They appear to be twinkling because they are of similar brightness

4. Quick Lab: Reading Star Charts
Use the handout to answer the following questions on your own.
In which constellation is Polaris ( the North Star) located?
What planet is shown in the constellation Capricornus?
Betelgeuse is a large star located in what constellation?
What is the name of the constellation that has three bright stars in a row?
What is the name of the star that seems to form the tail of the swan-shaped constellation known as Cygnus?
Is the star Aldebaran located east or west of Betelgeuse?
What is the name of the star cluster located midway between the constellations of Taurus and Perseus?
What large star seems to form the right foot of the constellation commonly referred to as Orion the Hunter?

5. Quick Lab: Answers
In which constellation is Polaris ( the North Star) located?
It is located in Ursa Minor or the Little Dipper.
What planet is shown in the constellation Capricornus?
Venus is shown in the constellation Capricornus.
Betelgeuse is a large star located in what constellation?
It is located in the constellation Orion.
What is the name of the constellation that has three bright stars in a row?
Its name is Orion.

6. Quick Lab: Answers
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.
Is the star Aldebaran located east or west of Betelgeuse?
Aldebaran is located west of Betelgeuse.
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.
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.

7. 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

8. 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!!

9. 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
Medium mass
High mass
Different masses have different lives!!

10. 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!!

11. 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

12. 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

13. 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
Black Hole

14. 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

15. 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

16. Life Cycles of Stars

17. Hertzsprung-Russell Diagram
Differences between stars include:
Colour
Brightness or Luminosity
Surface Temperature
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

18. 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

19. Hertzsprung-Russell Diagram
Patterns based on three star properties
Star data forms a distinct band from top L to bottom R
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