1. Space Chapter 19
Lives of Stars

2. Earth’s Most Important Star
Stars do not live forever
The sun, a medium star, is 93 million miles away from Earth
The sun gives us radiant energy for food, warmth and fuel
Some of the sun’s energy
is stored in the form of
fossil fuels, such as coal
and oil
Another form of energy
that comes from the sun is
invisible ultraviolet light

3. A Star is Born
A star is made up of a large amount of gas in a small volume of space
A nebula, is a large amount of gas and dust spread out in an immense volume
All stars begin as a nebula
A protostar is the earliest stage of a star’s life

4. Life times of Stars
How long a star lives depends on how much mass it has.
Small stars use up their fuel more slowly than large stars, so they have much longer lives.
Medium-mass stars live for about 10 billion years
Stars that have more mass than the sun have shorter lifetimes

5. Deaths of Stars
When a star runs out of fuel, it becomes a white dwarf, neutron star or black hole.
The center shrinks and the outer part expands.
White Dwarfs are the blue-white hot core of the star that is left behind
Neutron Star are smaller and denser than white dwarfs. After a star explodes, some of the material from the star is left behind.
Black hole are the most massive stars and has more than 40 times more mass than the Sun.
No light, radio waves or any other form of radiation can ever get out

6. Life Cycle of a Star

7. What are the characteristics of a star?
Stars differ in…
Mass
Size
Temperature
Color
Luminosity

8. Stars in Our Universe
The closest star to our solar system is the Alpha Centauri
It would take 30,000 boxes of salt to fill all the stars in our galaxy

9. Star Size
The diameters of stars range from as little as 1/10 the Sun’s diameter to hundreds of times larger.
The mass of stars can be from less than 1/100 to 20 or more times that of our Sun.
Stars over 50 times the Sun’s mass are extremely rare.
Our Sun is a medium sized star.

10. Star Temperature
Stars in the sky show tinges of different colors which reveal the stars’ temperatures.
Blue stars shine with the hottest temperatures and red stars shine with the coolest temperatures.
Our Sun is a yellow star having a surface temperature of about 5,500ºC
Stop and Think
The hottest flame color in a campfire is?
White/Blue

11. Star Colors A stars color reveals its temperature
The hottest stars—over 10,000 degrees Celsius—appear slightly bluer than the sun
A Blue-white Rigel is more than 15,000 degrees
With a surface temperature of about 5,500 degrees Celsius—appear white
The Sun glows white
The coolest stars—about 3,200 degrees Celsius—appear reddish in the sky.
Betelgeuse (red star on Orion’s shoulder) cool star

12. The Hertzsprung-Russell Diagram
Measures the brightness and surface temperature of stars.
More than 90% of all stars are main sequence stars
Star colors from Hottest to Coolest:
Blue, Blue-White, White, Yellow-White, Yellow, Orange, Red
O or blue is the hottest (>25,000oC)
M or red is the coolest (3,500-2,000oC)

13. Star Luminosity/Brightness
The brightness of a star depends upon the distance and its luminosity. The amount of light they give off!
Brightness depends on size and temperature
Stop and Think
The star Rigel in Orion is about 60,000 times larger than our Sun.
Why does our Sun appear brighter than Rigel?
9/17/2018

14. 1. Main Sequence Stars Upper left stars are Large, hot, luminous
90% of stars occur along the main sequence
Middle aged, stable stars
Main Sequence runs from upper left to lower right
Upper left stars are
Large, hot, luminous
Ex. Blue Giants
Lower right stars are
Small, cool, dim
Ex. Red Dwarfs
9/17/2018

15. Upper Right Stars Red Giants & Super Giants (Super Super Giants, too)
Large
Cool
Bright
1% of stars
Our sun in 5 billion years will be 2000 times brighter and 100 times larger (large enough to expand past Mars orbit)

16. Lower Left Stars
White Dwarfs (9% of stars)
Small
Hot
Dim