1. Chapter 10: Stars

2. What is a star?
The objects that heat and light the planets in a system
A star is a ball of super hot gas (plasma) held together by its own gravity
Nuclear reactions occur in stars (nuclear fusion of hydrogen gases to helium;
H  He)

3. I. Stars The Brightness of Stars
-Star: A hot glowing sphere of gas that produces energy by fusion.
-Fusion: The joining of separate nuclei. Common in nature, but not on Earth.

4. Characteristics of Stars
Magnitude (brightness)
A measure of brightness of stars
Apparent magnitude
How bright a star appears to be from Earth
Absolute magnitude
How bright a star actually is

5. Brightness
The brightness of a star is dependent size temperature and distance from Earth.
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.

6. 1. Actual vs. Apparent Brightness
Variables which affect a star’s brightness:
Star size
Distance from Earth
Star temperature
Apparent Brightness: The amount of light received on Earth from a star.
Actual Brightness: How large and hot a star is in relation to other stars.

7. Star Brightness
Example: Sirius has a greater apparent brightness then Rigel, even though Rigel is a much hotter and brighter star.
Why?

8. Characteristics of Stars
Temperature & Color
The color of a star indicates the surface temperature of the star
Below is the colors from hottest to coolest

9. 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.

10. Determining a Star’s Temperature
A star’s temperature can be determined by its color.
All objects will glow a different color when heated differently
Colors hottest to coolest: Blue/white  yellow  orange  red.

11. Star Size Dwarfs- small and mediums sized stars
The Sun is actually a medium sized star, it is just very close
Giant Stars- 10’s-100’s of times larger than dwarfs, and 100’s of times brighter
Supergiants- the biggest and brightest of the stars
Thousands of times brighter and hundreds of times bigger

12. Characteristics of Stars
DISTANCE
Measured in light-years
The distance which a ray of light would travel in one year
About 6,000,000,000,000 (6 trillion) miles
186,000 miles per second

13. Light-Years
Light-year: Distance light travels in one year. (Equal to about 9.5 trillion kilometers)
Approximate distances:
-Sun to edge of solar system = 5.5 light hours
-Nearest star (Alpha Centauri) = 4.3 light years
-Center to edge of Milky Way = 50,000 light years

14. Parallax
Astronomers have developed various methods of determining the distance of stars.
The change in position of a star in relationship to other stars 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

15. Kinds of Stars Variable Stars
A variable star is a star that regularly or repeatedly changes in magnitude
Pulsating variable star- has periods of swelling and shrinking
Eclipsing Variable Stars- occurs when pairs of stars orbit each other because of their gravitational pulls on each other

16. Pulsating Variable Stars

17. Variable Stars
Eclipsing Variable Stars

18. Kinds of Stars: Novas A nova is a new star
It is believed they form when an existing star suddenly flares up and becomes hundreds or thousands of times brighter

19. 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.

20. Kinds of Stars Nebula: A large cloud of interstellar gas and debris.
Dust and gas particles exert a gravitational force on each other which keeps pulling them closer together.
Orion Nebula

21. More Nebulas
As the particles pull closer together the temperature increases.
Another view of Orion

22. Kinds of Stars
When no more hydrogen is left in the core it explodes into a supernova.
This is the death explosion of a star
The star grows bigger and brighter and finally collapses

23. Kinds of Stars: Supernovas
Smaller stars become neutron stars
Pulsar: a neutron star that spins rapidly on its axis
Massive supernovas will collapse into a black hole.
Neutron Star

24. Life Cycle of Stars Life span of a star depends on its size.
Very large, massive stars burn their fuel much faster than smaller stars
Their main sequence may last only a few hundred thousand years
Smaller stars will live on for billions of years because they burn their fuel much more slowly
Eventually, the star's fuel will begin to run out.

25. 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.

26. Nothing (even light) can escape the gravity of a BLACK HOLE

27. Life Cycle of Stars

28. Life Cycle of Stars

29. Life Cycle of Stars
If the star is massive enough, the collapse will trigger a violent explosion known as a supernova
If the remaining mass of the star is about 1.4 times that of our Sun, the core is unable to support itself and it will collapse further to become a neutron star

30. Constellations
Constellations are groups of stars in patterns (animals, heroes… etc)
Stars that appear to revolve around the North Star are called circumpolar constellations

31. Astrology
Astrology is the study of how the stars and cosmos control or guide our lives
A type of religion for some
Astronomy is the scientific study of stars
How they form
Where they are located
Their size and composition

32. Telescopes
Refracting telescope- bend, or refract, light to make objects seem larger
Reflecting telescopes- produce a clearer image because the light is not bent, but rather reflected through a series of mirrors
Radio telescopes- collect radio waves (using a concave disk) to detect objects other telescopes cannot

33. Spectroscopes
They break down light given off a star into all of its colors

34. Spectroscope
Redshift occurs when an object moves away from the Earth the wavelengths become longer, causing the colors shift towards the red end of the color spectrum

35. Star Groups: Small Groups
Binary System is the smallest of star groups
It consists of 2 stars close together
Multiple Star Groups consists of three or four stars that stay close together

36. Star Clusters
Open Star Clusters a group of several hundred to a few thousand stars with no particular arrangement
Globular Cluster is a group of several thousand to a million stars arranged in a ball shape

37. Galaxies
A galaxy is a huge star system that has millions to billions of stars and covers many light years of space
We live in the MILKY WAY

38. The Milky Way Galaxy 100,000 light years in diameter
Our sun orbits the center of the galaxy once every 240 million years
Contains over 200 billion stars
Its where I live!!!!!

39. The Local Group Local groups are galaxies close to galactic neighbors
The Milky Way and Andromeda are in the local group

40. Space Objects
Asteroids- irregularly shaped pieces of rock, metal, and dust
Meteoroids- a chunk of metal or stone that is moving towards the Earth
Meteor- a meteoroid that has moved through Earth’s atmosphere and light’s up
Meteorites- meteors that hit the Earth’s surface

41. Space Objects
Comets are chunks of frozen gases, water and dust that orbits the Sun over and over again