StarsStarsStarsStars

What is a star?What is a star?

• A star is a ball of plasma held together by its own gravity– Nuclear reactions occur in stars (H

He)

– Energy from the nuclear reactions is released as electromagnetic radiation

Characteristics of StarsCharacteristics 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 per year

• 186,000 miles per second

Life Cycle of StarsLife Cycle of Stars

http://hea-www.cfa.harvard.edu/CHAMP/EDUCATION/PUBLIC/ICONS/life_cycles.jpg

Life Cycle of StarsLife Cycle of Stars

1. Begin their lives as clouds of dust and gas called nebulaeGravity may cause the nebula to contractMatter in the gas cloud will begin to condense into a dense region called a protostarThe protostar continues to condense, it heats up. Eventually, it reaches a critical mass and nuclear fusion begins.

2. Here begins the main sequence phase of the star. Most of its life is in this phase

Main Sequence StarsMain Sequence Stars

• A major grouping of stars that forms a narrow band from the upper left to the lower right when plotted according to luminosity and surface temperature on the Hertzsprung-Russell diagram

Life Cycle of StarsLife Cycle of Stars

Life span of a star depends on its size.3. Very large, massive stars burn their fuel

much faster than smaller stars4. Their main sequence may last only a few

hundred thousand years5. Smaller stars will live on for billions of years

because they burn their fuel much more slowly

6. Eventually, the star's fuel will begin to run out.

Life Cycle of StarsLife Cycle of Stars

7. It will expand into what is known as a red giant

8. Massive stars will become red supergiants

9. This phase will last until the star exhausts its remaining fuel

10.At this point the star will collapse

Life Cycle of StarsLife Cycle of Stars

11.Most average stars will blow away their outer atmospheres to form a white dwarf

12.Their cores will remain behind and burn as a white dwarf until they cool down

13.What will be left is a dark ball of matter known as a black dwarf

Life Cycle of StarsLife Cycle of Stars

14. If the star is massive enough, the collapse will trigger a violent explosion known as a supernova

15. 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

Life Cycle of StarsLife Cycle of Stars

16.The matter inside the star will be compressed so tightly that its atoms are compacted into a dense shell of neutrons. If the remaining mass of the star is more than about three times that of the Sun, it will collapse so completely that it will literally disappear from the universe. What is left behind is an intense region of gravity called a black hole

Life Cycle of StarsLife Cycle of Stars

http://www.seasky.org/cosmic/sky7a01.html

9. Scientists classify stars according to: _______, _______, & ________

10. A star’s color reveals its __________. The coolest stars glow ______, while the hottest stars glow ___________.

SIZE

BLUERED

BrightnessTemperature

Temperature

Types of StarsTypes of StarsClassificationClassification

Class Temperature Color

O 20,000- 60,000 K Blue

B 10,000 – 30,000 K Blue-white

A 7,500 – 10,000 K White

F 6,000 – 7,500 K Yellow-white

G 5,000 – 6,000 K Yellow

K 3,500 – 5,000 K Orange

M 2,000 – 3,500 K Red

Q: Based on its color, is our sun very hot? ___________

11. ___________ of a star depends on its ___________ and __________.

Brightness can be measured in terms of _____________or in______________.

NO

SIZE TemperatureBrightness

luminosity magnitude

13. _____________ is the measure of light stars generate from their surface. An incredibly bright star has a magnitude of -5 or more, an average star’s magnitude is close to 1, and a dim star’s magnitude is around 10.

12. __________ is how much power the star gives off as compared to our Sun. Our sun’s luminosity is 1.

LuminosityMagnitude

• 14. Each star is born, goes through its life cycle, then ___________.DIES

http://www.answers.com/topic/stellar-classification