Chapter 2                     The Universe               home page

I. The Universe

    A. Multiple-star systems

        1. Alpha Centauri

            a. Made of 3 stars (triple-star)

            b. Closest to the Earth (4.5 light years)

        2. Binary stars

            a. Double-star system

            b. Algol

    B. Constellations

        1. Groups of stars

        2. Big Dipper or Ursa Major - northern sky

        3. Little Dipper

            a. Has North Star (Polaris) on handle

            b. Also known as Little Bear

    C. Novas

        1. Stars that suddenly increases in brightness

        2. Slowly grows dim

    D. Star clusters

        1. Many stars grouped together

        2. Two types of clusters

            a. Open

            b. Globular

    E. Nebulae

        1. Mass of stars that shine with x-rays

        2.Birthplace of new stars

    F. Galaxies

        1.Major features of the universe

        2. Kinds of galaxies

            a. Spiral

            b. Elliptical

            c. Irregular

    G. Milky Way Galaxy

        1. Spiral shaped (pin-wheel shaped)

        2. Sun located on one of the spiral arms

        3. Stars rotate counter clockwise about the center

II. Formation of universe

    A. Stars on the move

        1. Moon moves around the earth

        2. Earth moves around the sun

        3. Sun moves around center of Milky Way Galaxy

    B. Red shift

        1. Star moving away from the Earth

        2. Doppler effect - change in wavelengths of light

    C. Big Bang theory

        1. Explosion of concentrated matter and energy

        2. Background radiation same throughout universe

    D. Open universe

        1. Universe continues to expand

        2. Leads to total emptiness

    E. Closed universe

        1. Expansions stops

        2. Galaxies pulled toward each other

        3. Blue shift occurs

    F. Quasars

        1. Most distant objects

        2. Give off radio waves and x-rays

        3. 1st objects formed after Big Bang

III. Characteristics of stars

    A. Size

        1. Giant

        2. Supergiant

        3. White dwarf

        4. Neutron

    B. Composition

        1. Hydrogen, most common element

        2. Helium, second most common element

    C. Surface temperature

        1. Color determines surface temperature

        2. Blue light

            a. Hottest stars

            b. 50,000˚C

        3. Red light

            a. Coolest stars

            b. 3,000˚C

    D. Brightness

        1. Depends on size, surface temperature, distance from Earth

        2. Magnitudes of stars

            a. Apparent (star's brightness as appears on Earth)

            b. Absolute (actual amount of light star gives off)

        3. Variable stars

            a. Star changes in size

            b. Star changes in brightness

    E. Hertzsprung-Russell diagram

        1. Shows relationship between absolute magnitude and temperature

        2. As one increases so does the other

        3. Main-sequence stars range from blue/white to red stars

    F. Measuring distance

        1. Parallax - used to measure distance of star closest to Earth

        2. Magnitudes determine distance more than 100 light-years away

        3. Spectroscope used for more than 7 million light years away

    G. Why stars shine

        1. Nuclear fusion

        2. Produces energy in form of heat and light

IV. Special star:  our sun

    A. Layers of sun

        1. Corona

        2. Chromosphere

        3. Photosphere

        4. Core

    B. Active sun

        1. Prominences - arches or loops of gases

        2. Solar flares - bursts of light

        3. Solar wind - continuous stream of high-energy particles

        4. Sun spots - dark areas on sun's surface

V. Evolution of stars

    A. Protostars

        1. Result of heat given off during nuclear fusion

        2. Shines, gives off heat and light

        3. Star is born, mass determines size

    B. Medium-sized stars

        1. Change hydrogen to helium in core

        2. Outer shell expands and cools

        3. Red giant formed

        4. Helium atoms fuse into carbon atoms

        5. Star dies, becomes white dwarf

    C. White dwarf

        1. Made of dense matter

        2. Shines with hot white light

    D. Massive stars

        1. Become red giants or supergiants

        2. Gravity pulls carbon atoms together in core

        3. Heavy elements form - iron

    E. Supernovas

        1. Nuclear fusion stops in massive stars

        2. Explosion occurs

        3. Cloud of dust and gases forms (nebula)

    F. Neutron stars

        1. Star that has 1.5 to 4 times mass of sun

        2. Spin rapidly, energy given off as pulses

        3. Pulsars are formed

    G. Black holes

        1. Stars with mass more than 10 times that of sun

        2. Core left after supernova

        3. Swallowed up by own gravity (cosmic vacuum cleaner)