STARS

1. By: Besas, Jemarie D. Espuerta. Ma.Frechilyn Joy C. September 3, 2012 STARS

2. WHAT IS A STAR?

3. A huge ball of ionized gas • A body that at some time in its life generates its lights and heat by nuclear reactions, specifically by the fusion of hydrogen into helium under conditions of enormous temperature and density.

4. WHAT ARE CONSTELLATIONS? • names for groups of stars that appear to form shapes in the sky. They were given their names many hundreds of years ago to help us remember which stars are which. We used constellations to divide up the sky: finding one can help us find another because constellations

5. move so slowly that in our lifetime, they will always be found in about the same place.

6. STELLAR PROPERTIES A. TEMPERATURE Wien’s Law : “The hotter the star is, the shorter the wavelengths it emits.” Thus, HOT STARS will appear BLUE and WHITE while COOL STARS will be RED.

7. B. LUMINOSITY - the amount of energy a body radiates each second. Inverse Square Law for Luminosity: “ As light spreads out from a source, it spreads over progressively larger areas as the distance from the source increases.”

8. Absolute Magnitude is the star’s actual brightness. • Apparent Magnitude is how bright stars appears on Earth. • The higher the number, the dimmer is the star.

9. C. RADIUS Stefan Boltzmann Law: “ The luminosity of an object depends on its temperature.” Thus, an increasing temperature or radius of a star makes it more luminous.

10. D. COMPOSITION “ The spectrum of a star is the amount of energy it emits at each wavelength. As light moves from its core to its surface layers, atoms absorb the radiation at some wavelength, creating dark absorption line that tells the composition of the stars.”

11. E. SPECTRAL CLASS O, B, A, F, G, K, M, where O is the hottest and Mis the coolest

12. EVOLUTION OF STARS • Stars come from interstellar gases drawn together by gravity which compresses and heats the gas forming a protostar. • Further heating of the protostar’s core will lead to the fusion of hydrogen into helium accompanied by a tremendous

13. release of energy. This release of energy keeps the stars hot. • It creates pressure that balances and stops the gravitational pull, changing protostar into a Main Sequence Star. • The amount of interstellar gas determines the size of the star, larger

14. amount of interstellar gas, the larger is the star. Yet, the bigger the star, the shorter is its life span. • As soon as the hydrogen in the core of a massive stars is exhausted, the core shrinks and heats up, turning the star into a giant.

15. A star of low mass like the Sun continues to burn hydrogen but eventually compresses the helium in the core to start another nuclear fusion, turning it into a yellow giant. • As it burns helium, the core further shrinks to form a small

16. dense star, a white dwarf. • Giant stars have more dramatic end. Because of the tremendous heating from gravitational compression of their cores, they can ignite fuels in their core easily, forming other elements such as

17. carbon, neon, silicon and eventually iron. Since the iron core cannot burn and will collapse, it triggers a supernova explosion. shrinks again, turning it into a red giant once more. The outer layer is then driven off a planetary nebula shell. The core

18. The core produces a neutronstar, or in the case of a super giant which continues to collapse, a BLACK HOLE

19. BLACK HOLES • The intense gravitational field left when a giant star collapses. • It is called a black hole because not even light can escape.

20. THANK YOU 