Kinds of Stars

Stars & Galaxies Chapter 21

Stars & Their Characteristics 

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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) 

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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.

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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   

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

Kinds of Stars 

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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 

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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  

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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 

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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 

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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 XRays that are detected by radio telescopes. 

Galaxies and the Universe 

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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 

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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 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. 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

Super Giants – Hundreds of times brighter than