1. STARS & Galaxies Chapter 15 Chapter 15

2. What is a star? Huge, hot collection of gases so dense act as solids. Birth of a star: Starts as a ball of gas/dust Gravity pulls it inward Temp Nuclear fusion and then….. A star is born !!!

3. Types of telescopes Refracting-use convex lenses to gather and focus light Reflecting-used curved mirrors to collect and focus light Radio-uses devices to collect radio waves from objects Other telescopes-some use infrared radiation, ultraviolet radiation, x-rays and gamma rays, *space telescopes-example Hubble

4. Electromagnetic radiation Light-can travel through space in the form of waves Visible light-all of the colors that you can see (ROY G BIV) Electromagnetic spectrum- includes the entire range of radio waves, infrared radiation, visible light, ultra violet radiation, x-rays and gamma rays

5. Stars Constellation-imaginary patterns of stars Classification- –color& temperature- correspond to each other, blue, white, yellow, orange and red is (hottest to coolest) - size-super giants, giants, large, medium, dwarf and neutron stars (largest to smallest) –Brightness-dependent on size and temperature –Composition-vary in stars, but is about 73% hydrogen, 25% helium, and 2% other

6. Life Cycle of a Star Shown and Classified with the H-R (Hertzsprung-Russell) diagram which shows the relationships b/w temperature (colors) and magnitude. (also shows life cycle stages) Absolute Magnitude– actual brightness of star (if they were all the same distance away) Apparent Magnitude– brightness as seen from Earth Smaller the magnitude # = brighter the star

8. Classification Table Colors Surface Temp ºC Example Blue > 30,000 10 LaCertae Blue-white 10-30,000 Rigel Blue-white 7500-10,000 Vega & Sirius Yellow- white 6000-7500 Canopus Yellow 5000-6000 Sun Orange 3500-5000 Arcturus Red < 3500 Betelgeuse

9. Types of Stars Blue Stars – very massive, use up their hydrogen very fast, expand into…. Giants/Supergiants – star out of hydrogen, center shrinks, outer part expands, cools, becomes red giant; if massive a supergiant

10. White-dwarf - small hot shrunken centers, near end of life. Red-dwarf – very low mass, and very, very old (some of the oldest stars in the galaxy)

11. Supernovas – large blue star that may explode – Death of a star. Black Hole – supernova is so massive that it collapses (10km across); gravity is so strong that not even light can escape.

12. Neutron Stars – formed from remains of explosion of Super-giant Pulsars – spinning neutrons (emit steady beams of radiation in narrow cones)

13. Star Systems Multiple star systems –Binary stars-star systems that have 2 stars, one is usually brighter and more massive, the smaller dim star often causes the first to wobble Eclipsing binary –Sometimes a dim star passes in front of the brighter star, eclipsing it Star clusters –Open cluster-loose disorganized appearance –Globular cluster-large group of older stars that are round and densely packed

14. Galaxies-a huge group of single stars, star systems, star clusters, gas & dust, bound together by gravity Spiral – bulge in middle with arms spiraling outwards; Milky Way Elliptical – shaped like an oval or an egg; contain billions of stars Irregular – no regular shape and usually smaller with many bright young stars

15. The Milky Way Our solar system is located in a spiral galaxy called the Milky Way We are in one of the spiral arms

16. Expanding Universe Formation –Began billions of years ago –Big Bang-huge explosion Moving galaxies-expanding away from each other Cosmic background radiation-distributed in every direction as the universe expands The universe is 13.7 billion years old

17. Solar nebula-5 billion years ago a giant cloud of gas and dust collapsed on itself to form our solar system Dark matter-makes up 90% of matter in galaxies, does not give off electromagnetic radiation, still somewhat of a mystery Accelerating expansion-the expansion of the universe is accelerating and may be caused by dark energy