1. Beyond Our Solar System – The Universe in a Nutshell!
Chapter 25

2. Star Temperature Color is a clue to a star’s temperature
Very hot (30,000 K) stars emit their light in the blue spectrum, red stars are much cooler, stars with temperatures between 5000 and 6000 K appear yellow

3. Binary Stars
Binary Stars – pairs of stars, pulled together by gravity, that orbit each other
Binary stars are used to determine the star property most difficult to calculate – its mass

4. Parallax
The nearest stars have large parallax angles, while those of distant stars are too small to calculate
Light-Year – unit used to express stellar distance, the distance light travels in one year (~9.5 trillion kilometers)
Our closest star (besides the sun), Proxima Centauri, is about 4.5 light-years away from the sun

5. Stellar Brightness
Apparent Magnitude – a star’s brightness as it appears to Earth
Absolute Magnitude – how bright a star actually is

6. A Hertzsprung-Russell diagram shows the relationship between the absolute magnitude and temperature of stars

7. Nebulae – clouds of dust and gases in space
Reflection Nebula in Orion
Dark Nebula – Horsehead Nebula
Emission Nebula – N11

8. The Birth of a Star
The birthplaces are dark, cool interstellar clouds (nebulae)
The initial contraction of the nebula can be triggered by the shock wave from an explosion of a nearby star
The Orion Nebula in normal color and infrared

9. Protostars in the Horsehead Nebula are circled
Protostar – a developing star not yet hot enough to engage in nuclear fusion
When the core of a protostar has reached about 10 million K, pressure within is so great that nuclear fusion of hydrogen begins, and a star is born
Protostars in the Horsehead Nebula are circled

10. Main-Sequence Stage – From the moment of birth until the star’s death
The more massive a main-sequence star, the shorter its life span
A yellow star, like our sun, can remain in the main-sequence for approximately 10 billion years

11. The Sun will spend less than 1 billion years as a Red-Giant
Red-Giant Stage
The Sun will spend less than 1 billion years as a Red-Giant
Globular Star Cluster, some of the oldest stars in the universe

12. White Dwarf – remains of low and medium mass stars, extremely small stars with densities greater than anything on Earth

13. Life Cycle of a Sun-like Star

14. Neutron Stars – remnants of supernova events, stars that are smaller and more massive than white dwarfs

15. Black Hole – A massive star that has collapsed to such a small volume that its gravity prevents the escape of everything, including light

17. Stellar Evolution

18. The Milky Way Galaxy
Galaxies – groups of stars, dust, and gases held together by gravity
The Milky Way is a large spiral galaxy whose disk is about 100,000 light-years wide and about 10,000 light-years thick at the nucleus
It has at least three distinct spiral arms, the sun lies about 2/3 of the way from the center on one of these arms and orbits the nucleus about every 200 million years
There may be more than 100 billion stars in our galaxy alone

19. Structure of the Milky Way

20. Spiral Galaxies – like our galaxy, these galaxies have multiple arms that sweep out from a central nucleus

21. Elliptical Galaxies – do not have spiral arms, makes up ~60% of known galaxies, can range from round to oval

22. Irregular Galaxies – consist mostly of younger stars, appear as clouds of stars

23. Galaxy Cluster – a system of galaxies containing from several to thousands of member galaxies

24. The Expanding Universe
Hubble’s Law – galaxies are retracting from us at a speed that is proportional to their distance
The red shifts from distant galaxies indicate that the universe is expanding

25. Big Bang Theory – The universe began as a violent explosion from which the universe continues to expand, evolve, and cool
The big bang theory states that at one time, the entire universe was confined to a dense, hot, supermassive ball. Then, about 13.7 billion years ago, a violent explosion occurred, hurling this material in all directions