Stars & Galaxies

Chapter 21

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.

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.

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.

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.

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)

Stars & Their Characteristics

Brightness – – Apparent Magnitude – How bright a star

appears from the Earth’s surface.

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

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.

Kinds of Stars Eclipsing Binaries- When one star rotates

around another brighter star. The stars look like 1 star that changes brightness.

Pulsars- 1967 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.

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”

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.

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.

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 1987. (Page 387 text) Figure 21.10

NEUTRON STAR – Mass that remains after an exploded SuperNova.

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.

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.

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.

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.

Science Background Polaris is a cepheid variable with a

period of just 4 days. Its magnitude is only 2.5 to 2.6. 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.

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.

Ch 21Vocabulary WordsAbsolute 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. 150 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. 9. 5 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