STARS AND BEYOND
Teacher Outline
* Teacher Outline included in Teacher Guide Download

1. GALAXY - A large collection of stars, dust, and gas in space. A system of millions or billions of stars held together by gravity. Examples include our own Milky Way.

1. BINARY STAR - A system of two stars, orbiting around on another. Binary (and other multiples) stars are very common. Astronomers estimate that about half of all stars are members of multiple-star systems.
     
2. BLACK HOLE - An object whose gravitational pull is so strong that nothing can escape, not even light. Black holes have recently been verified.
     
3. GLOBULAR CLUSTER - A large congregation of stars which is spherical in form.
     
4. NEUTRON STAR - The central core of an exploded star as an object even smaller and denser than a white dwarf.
     
5. STAR - A mass of gas that is self-luminous. There are several stages of a normal star including the major groups including white dwarfs, main sequence, giants, and supergiants.

1. WHITE DWARFS - A star that has about the same mass, but much smaller diameter, as an ordinary star; a white star several magnitudes below the main sequence.
     
2. MAIN SEQUENCE - Stars that are typical, including our Sun and the majority of the stars in the Universe.

1. SOLAR SYSTEM - Contains one star and planets.

1. PLANETS - Bodies that orbit around a star. Presently only one of nine bodies that revolves around the Sun. Theoretically, planets are suspected to orbit other stars similar to the Sun, which is part of the main sequence of stars. There is evidence for protoplanets in the Orion sector.
     
2. COMET - A body that orbits around the Sun, Theoretically predicted to be found in other systems.
     
3. ASTEROID - Small objects in orbit between Mars and Jupiter.

3. GIANTS - A large star of about zero absolute magnitude.
     
4. SUPERGIANTS - A large star of absolute magnitude greater than -0. Brighter than a giant.

6. PULSAR - Radio pulses from over several hundred sources within galaxies.

2. QUASARS - Objects that emit as much energy as hundreds of galaxies from an area less than a light year in diameter.

1. The evolution of the Universe includes all the various objects. Did the Universe start all at once, were the stars and planets just there in a few seconds, or did it slowly evolve to the position that we see today?
     
2. Scientists feel that the Universe may still be creating and destroying mass. When astronomers look into the sky, they see supernovas or large explosions in the sky. They see movement of the Universe which suggest that the Universe is still evolving.
     
3. Some scientists suggest that the Universe started as matter, totally unlike anything we know today, which started to expand and was probably 10²³ Kelvin (very high temperature).

1. As the expansion continued the temperature dropped steadily until it reached 3 Kelvin. Shortly after this, the four interactions (gravity, electromagnetism, weak and strong nuclear) appeared from the matter that was created.
     
2. The early Universe consisted of a hot "soup" of quarks, leptons, and photons. Matter and antimatter had a fight, and matter became the dominant form. Protons and neutrons joined the light nucleus of Hydrogen, Helium and Lithium. Atoms continued forming into galaxies, then stars and planets.
   

4. Time-Table of Events

1. The Big Bang Occurred. All interactions, gravity, strong nuclear, weak nuclear, and electromagnetism are unified. The radius of the Universe is less than 10^-50 centimeter. A very small area.
     
2. 10^-43 seconds later.Gravity separated from the other forces. Inflation of the Universe occurs. Inflation refers to the tremendous expansion of the early Universe. The observable Universe expands to approximately the size of a grapefruit.
     
3. 10^-35 seconds after the Big Bang. Strong nuclear force separates from electromagnetism and weak nuclear. Inflation ends. Universe consists of hot electron-quark soup. (Remember a quark is a particle inside the nucleus.)
     
4. 1 second after the Big Bang. Electromagnetism and weak nuclear force separate. Quarks combine to form protons, and protons and electrons combine to form neutrons. Helium and other light elements form through nucleosynthesis.
     
5. 1 million years after the Big Bang. The universe becomes transparent. Matter releases radiation, which becomes detectable later as cosmic microwave background.
     
6. 1 billion years after the Big Bang. Protogalaxies begin to form, but most are still beyond the range of current instruments.
     
7. 3 billion years after the Big Bang. Quasars and some radio galaxies are detectable.
     
8. 8 billion years after the Big Bang. Most galaxies, including the Milky Way are formed.
     
9. 13 billion years after the Big Bang.The Sun and planets form.

1. Stars are balls of gas that emit energy created by nuclear reactions within the star. There are many sizes and brightness of stars.
     
2. Stars are classified according to their brightness and temperature. They range in temperature from super hot blue-white stars (over 20,000E) to cool red stars (3,000EC). Our Sun is a medium yellow star. The current theory suggests that stars are born in nebulae, interstellar gas clouds.

1. The Hertzsprung-Russell Diagram plots stellar luminosity (brightness) with surface temperature.
     
2. Main sequence stars follow a distinct path after birth called the Hayashi Tracks, with reflect a star’s age.

3. Stars are forming today. An example is the Orion Nebula (sword of Orion the Hunter) where stars are being born at this moment. Stars also die. Older stars are called red giants and supergiants, and are closer to dying.

1. The term galaxy refers to a large collection of stars, dust, and gas clouds which are held together by gravitational attraction. Hubble, a well known astronomer classified galaxies into 3 major groups.

1. Ellipsoidal, spiral, and irregular galaxies are terms that describe the general shape and help describe the formation of the galaxies.
     
2. A nebula is a concentration of stars and protostar material without a set pattern.

2. Galaxies tend to cluster together within the Universe. For example our companion galaxies include the Magellanic Clouds and the Andromeda Galaxy. They can be seen on the celestial globe as what most would mistake as stars, because they seem so small

1. Magellanic Clouds are near the -70E between 6h - 5h as a purple cloud. Andromeda is also called M31 and is located +40 between 1h and 0h. Around our galaxy are greater than 100 ball shaped clusters of stars known as globular clusters which are 100,000 millions of stars bound together by gravity.

3. The amount of space that these galaxies take up is immense. They are measured in light years (or the distance that light travels in one year or about 9.4 trillion km). It is difficult if not impossible to accurately measure the distances to galaxies.

1. The nearest galaxies are the Magellanic Clouds which is 160,000 light years away with a diameter of 30,000 light years and the Andromeda Galaxy which is 870,000 light years away with a diameter of 45,000 light years.
     
2. Our own galaxy is thought to be 250,000 light years in diameter with a width of 100,000 light years, but this changes depending on the astronomer who does the measurements.

4. Types of galaxies

1. ELLIPSOIDAL GALAXIES - Symmetrical structure ranging from spheres to flattened ellipsoids (in cross section). Usually the type of stars are older type of stars called Population II.
     
2. SPIRAL GALAXIES - A galaxy that has a distinct nucleus and one or more spiral arms. The arms extend outward from the nucleus and are composed of stars, dust, and gas. Population I stars are found in the arms and Population II in the nucleus, between arms and probably in the halo. Population I are considered younger stars. There are 2 distinct classes of spirals:

1. a. NORMAL SPIRAL - several arms radiate from center (top view)
     
2. BARRED SPIRAL - have elongated centers, called bars, with arms, coming from each end (top view).

3. IRREGULAR GALAXIES - no regular shape (including nebula)

5. The shape of galaxies is thought to represent different stages in the evolution of the structures. However, this is a little complicated, and would have to address how the Universe was formed.

1. Astronomers locate objects by assuming the sky is a spherical surface called a celestial sphere.

1. The angles between objects helps to locate objects. The north and south celestial poles are those portions of the sky that seem fixed. That is why we call Polaris the "North Star" because we in the Northern Hemisphere seem to rotate around it.
     
2. You can use an open umbrella as an example. The pole would be the North Star and as you rotate the umbrella that is how the Northern Hemisphere seems in the night sky.

2. A constellation is an apparent grouping of stars named for a mythical figure, animal or inanimate object. There are 88 constellations. Familiar ones include Andromeda, Hercules, and Pegasus.

1. About 8 degrees on both side of the ecliptic (the apparent path of the Sun among the stars) are 12 constellations referred to as the 12 signs of the zodiac. Because of the Earth's motion around the Sun, the Sun is at Pisces at the beginning of spring and then moves at the rate of one constellation per month, in the order of Pisces, Aries, Taurus, and so on.
     
2. The stars that make up the constellations are within our own galaxy, the Milky Way, and other galaxies in the Universe. Constellations are an apparent association of stars, that are many light years away. Many of these stars are very far from each other. The constellations were very important to early people, because it allowed them to find directions during the night. This would help them navigate on land and sea. The constellations also revealed to early farmers, when spring and summer was approaching, by the changing constellations at night
     
3. The changing of the constellations at night were more accurate than watching the Sun rise and set every morning. The constellations and the charting of their movement were done by astrologists.

1. In early times, astrologists were regarded more as scientists because of their ability to chart the night time sky. However, today charting the movement of the starts and developing stories of romance and business, is not scientific.