1. Stars & Galaxies
Chapter 21

2. Stars & Their Characteristics
Constellation – Group of stars that appears to form a pattern. 88 recognized by science.
Ursa Major – “Big Bear”, “Big Dipper”
Ursa Minor - “Little Bear”, “Little Dipper”
Cassiopeia – Lopsided “M”, Queen’s Chair
Circumpolar Constellations – Constellations that appear to move around the North Star.

3. Stars & Their Characteristics
Polaris – “North Star”
Apparent movement of circumpolars caused by rotation on axis.
Seasonal Constellations –
Summer Triangle
Orion
Constellations lost in sunlight at different times of the year.

4. Stars & Their Characteristics
Summer Triangle – 3 Stars
VEGA in the constellation Lyra (The Harp)
Altair in the constellation Aquila (The Eagle)
Deneb in the constellation Cygnus (The Swan)
Deneb at the top of the “Northern Cross”.
Orion – “The Hunter” Winter Constellation
BETELGEUSE & RIGEL
Belt stars help locate two other constellations.

5. Stars & Their Characteristics
Left of belt is SIRIUS of the constellation Canis Major.
SIRIUS-Brightest star in the nighttime sky.
Right of belt is Taurus the Bull, Pleides.
Distances to Stars
Astronomical Unit (AU)- Average distance from our sun to the Earth.
150 Million Kilometers
Alpha Centauri next nearest star to us. 300,000 x as far from Earth as we are from the sun.

6. Stars & Their Characteristics
Stars – Most are different in density.
Less different by mass.
Color of star depends on surface temperature.
Hot stars are Blue, Cooler stars are Red.
Made mainly of Hydrogen and Helium.
Our sun is 70 % Hydrogen/ 28 % Helium.
Each star has its own spectrum. (Fingerprint)

7. Stars & Their Characteristics
Brightness –
Apparent Magnitude – How bright a star appears from the Earth’s surface.

8. Kinds of Stars Red Giants - ALDEBARAN, ARCTURUS
Blue-white- hot, SIRIUS, VEGA
SUPERGiants- More luminous, greater in size. Include blue-white RIGEL, White-yellow CANOPUS, red SuperGiants ANTARES & BETELGUESE.
REDSUPERGIANTS- Largest of all stars

9. Kinds of Stars Dwarf stars – Absolute magnitude of less than 1.
Most either red, orange, or yellow.
White dwarfs – very faint, small, dense.
Variable stars – Shine with different brightness over several day periods.
Pulsating Stars- Change brightness, expand & contract. Example is Cepheid Variables.

10. Kinds of Stars
Eclipsing Binaries- When one star rotates around another brighter star. The stars look like 1 star that changes brightness.
Pulsars Jocelyn Bell-Burnell. Crab Nebula discovered. Both radio waves and light came from a star in this nebula. Pulse due to rapid rotation of star.

11. Formation of Stars Nebulae – Clouds of dust or gas in space.
Nebula dust seen by 2 methods:
1. Light from nearby star is reflected off dust.
Example is a DIFFUSE NEBULA
Brightest known is in constellation ORION.
2. Nebulae clouds contact each other and glow. These are called PROTOSTARS.
Dark Nebulae- Away from stars. “HorseHead”

12. Formation of Stars Gas and Dust in space are called Nebulae.
Stable State – Stars whose diameter and radiation stay the same for millions of years. Our sun is in a stable state.
When fusion doesn’t balance gravity’s force, core contracts(gets hotter) and outer layers expand.
Star is bigger, brighter, more surface area.

13. Formation of Stars
Dwarfs – Core temperature and pressure not enough to support outer layer(s) weight.
Star collapses and becomes very dense.
Occasional flare ups called “NOVAS”
NOVA – “new star”
Our sun – Stable now, will become Red Giant, fade to White Dwarf.

14. Formation of Stars
SUPERNOVA – 1054 Chinese observed one. It’s remaining dust cloud “Crab Nebula” found in Taurus the Bull.
Best known modern SuperNova appeared in (Page 387 text) Figure 21.10
NEUTRON STAR – Mass that remains after an exploded SuperNova.

15. Formation of Stars
BLACKHOLES - Object of space with high gravitational pull. Light cannot escape.
Atoms are ripped apart before entering a Blackhole. These atoms emit X-Rays that are detected by radio telescopes.

16. Galaxies and the Universe
Most galaxies are millions of light years away.
Our sun is one star of 100 billion in the MILKY WAY Galaxy.
Milky Way – 140,000 LY long, 20,000 LY thick. Sun is 23,000 LY from its center.
Local Group – Small cluster of 17 galaxies.

17. Galaxies and the Universe
Nearest galaxy is the ANDROMEDA Galaxy at 2 million LYs away.
Galaxy Types:
Spiral – Bright center, usually two arms that hold majority of its stars. ( ¾ of galaxies)
Elliptical – spherical shape, most stars in the center. No arms, gas, or dust.
Irregular- No set shape, least common.

18. Galaxies and the Universe
QUASARS – Discovered in 1961
Very far away
Calculated to be the most luminous objects in space.
Larger & more massive than stars.
High radiation emission.

19. Science Background
Polaris is a cepheid variable with a period of just 4 days. Its magnitude is only 2.5 to Polaris is a double star. Its companion has a magnitude of 8.8.
Scientists compare a Cepheid’s absolute and apparent magnitudes to determine its distance from Earth.

20. Science Background
Proxima Centauri – Closest star to Earth. Its magnitude of 11 is no visible to unaided eye.
Alpha Centauri – Closest VISIBLE star to Earth with the unaided eye.
Both Centauri stars can only be seen at locations within 30 degrees of the south pole.

21. Ch 21Vocabulary Words
Absolute magnitude - The brightness of a star compared to other stars if they were compared at the same distance.
Constellation – A group of stars that appear to form a pattern.
Apparent magnitude – The brightness of a star as it appears from Earth.
Dwarf Stars – Stars that have gone to the unstable state. The inner core collapses and the star is very dense.
Astronomical Unit (AU) – The average distance between the sun and the Earth million kilometers.
Eclipsing Binary – Two stars that are in rotation around each other. One is brighter than the other. Looks like 1 star.
Big Bang Hypothesis – Theory of how the universe first started.
Galaxies – Collections of billions of stars. Three types include spiral,elliptical, and irregular. Local Group
Luminosity- The actual brightness of a star as it appears from just outside of the Earth’s atmosphere.
Light-year – The distance light travels in one year trillion kilometers. (300,000 kilometers per second)
Nebulae – A collection of space dust and gas. This is the ingredients for starting a new planet.
Protostar – When two nebulae clouds rub together and cause a glow.
Neutron star – The mass that remains after a star goes supernova.
Pulsar – Stars that emitt radio waves that are in time with the visible light waves that it also emitts. “Crab Nebulae”
Nova – “New Star”
Quasars – The most luminous objects in space. Very large. Very, very far away. Bigger than super giant stars.
Black holes – Invisible objects in space that have a gravitational pull so strong that no EM energy can escape.
Red Giants – Highly luminous stars that are considered to be “warm” compared to other stars. Aldebaran Arcturus
Cepheid Variables – Yellow super giant stars that have a variable bright to dim period.
Super Giants – Hundreds of times brighter than super giants. Rigel, Betelguese, Canopus