Scientists study stars and the universe using:

    1. Telescope: simple magnification of visible light.

    2. Spectral Analysis: divides the spectrum of electromagnetic energy into different wavelengths.  By selecting specific    wavelengths, information about a star can be determined including  temperature, motion, relative temperature,  composition
and the presence of a magnetic field.

Stars are bodies of high temperature and high pressure.  The star closest to Earth is the Sun.
Distances between stars and other objects in the Universe is measured in light years.  A light year is the distance light will travel in a year.

Most scientists believe that most stars are somewhat similar to the Sun.

The Sun:

The Sun is composed of hydrogen and helium.  It is believed to have a gaseous center with large convective movements through the gas.

Photosphere: The surface of the Sun

Chromosphere: the area above the photosphere, also called the solar atmosphere.  An area of thinning hydrogen and helium that extends out from the Photosphere.

Prominences: Large sprays of gas that extend up to 200,000 km out into space from the Sun's Surface.

Flares: Hot gas flowing out from sunspots.

Sunspots: appear as dark areas on the Sun, sunspots are areas of cooler temperatures.

Corona: The outer portion of the Sun's atmosphere, seen only during an eclipse.

Interesting Statistics:
 

• 109 Earths would fit across the face of the Sun
• The interior of the Sun could hold 1.3 million Earths
• The surface temperature is 11,000 ^oF
• The interior temperature is estimated to be 27 million ^oF
• Sunspot temperatures are estimated to be 7,000 ^oF
• The interior pressure is 340 billion times that of Earth

Although stars differ in their size and temperature they have similar origins and similar evolution.
They are composed primarily of hydrogen and helium.
 

The Life History of a Star:

I) Birth: Stars are believed to originate as from gas clouds in space.  Gravitational forces cause this gas to contract forming a dense center of gravitational force.  Over time the gravitational forces cause the star to draw in more and more gas, contracting further.  Eventually this extreme pressure at the center of the star causes nuclear fusion reactions to occur.

[A fusion reaction occurs when two small atoms (hydrogen) combine (to form helium) and release energy.]

A star is born!!!

II) Main Sequence: the main sequence is a time of stability.  Gravitational forces act to contract the star.  Fusion reactions and heat convection act to expand the star.  The two forces are balanced and the star remains stable in size and reactions.  The star remains stable as long as hydrogen exists to combine in fusion reactions.  Once all the hydrogen has been converted to helium the star is unstable.
 

III) Death: A star starts to disintegrate once all the hydrogen has been converted to helium.  This process depends on the size of the star.

A) Small Star:

Once all the hydrogen is used up in a smaller star it will start to contract due to gravitational force.  The
contraction increases pressure at the center of the star and increases the temperature in the star.  The increase in temperature and pressure facilitate other fusion reactions involving helium.  These fusion reactions cause the star to expand outward forming a Red Giant.

Red Giant phase: of the star is relatively short.  During this time the star is using helium in fusion reactions. Gravitational forces once again act to contract the star  but are once again balanced by forces from fusion reactions acting to expand the star outward.  Red giant stars are relatively cool on the outside with a hot core in the center.

White Dwarf Stage: occurs when all the helium is used in fusion reactions.  The outward force no longer balances gravitational force and the star collapses inward becoming a white dwarf.  Some fusion is occurring in the core of the star but mostly the star glows from remnant heat.  The white dwarf stage is very long.

The Sun is a small star believed to be halfway through its main sequence.  When it becomes a Red Giant it will expand out to the orbit of Mars.  In its white dwarf stage it will be smaller than the Earth.

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B) Large Star:

Large stars use up their hydrogen at a faster rate than small stars.  Once all the hydrogen has been converted to helium the star begins to contract.  Because there is so much more mass the star collapses abruptly causing a violent explosion known as a Super Nova.  The explosion occurs because the nuclei of the helium in the star are pushed together suddenly and repel each other causing the explosion.  A VERY BRIGHT light is emitted by the super nova explosion.  Most of the star's mass is thrown out into space leaving only a small portion of the original star.  The Crab Nebula was formed from the remains of a super nova that exploded in 1054 AD.

[A super nova occurred in 1987 and was visible in the Southern Hemisphere.  This is the first one visible with the naked eye since the 1600's. ]

Neutron Star: a very dense very small star that is the remnant of a super nova explosion.  It is much smaller than a white dwarf.
Pulsar: believed to be a rotating neutron star.

Black Hole: an area of INTENSE gravitational force.  The gravitational force is so great that light cannot escape and that area of space appears as a black hole.  It is theorized that black holes may form when a very large star collapses so suddenly that it produces an intense gravitational field.
 

The Universe

The universe is made up of galaxies, galaxies are made up of stars.  Galaxies can be widely spaced from one another or can be close together and even collide.  Galaxies tend to rotate in a circular pattern, most are shaped in some variation of a spiral form.

The solar system that contains Earth is located in the Milky Way galaxy.

Many wonderful objects exist in the galaxy... three that have not been discussed so far.
 

1. Galactic Cluster (open cluster): concentrations of  dozens to hundreds of stars that are loosely arranged as a group with a common motion. All ages and types of stars can be found in an open cluster.  The stars can be loosely or tightly clustered,  the defining characteristic is the common motion.

2. Globular Cluster: Closely packed stars in a ball shaped arrangement.  All the stars in the cluster are the same age...very old.  Globular clusters contain thousands to hundred of thousands of stars.

3. Galactic Nebulae:  dust and gas clouds that occur in space.  The glow from emitted and reflected radiation.  It is believed that nebulae are the birth place of stars.  Planetary nebulae are believed to be the birthplace of planets.  Planetary nebulae do not emit radiation so are not as visible in the sky.