1. Stars

2. Distances To The Stars Measuring_Distance_in_Space__The_Light_Year
Stars are separated by vast distances.
Astronomers use units called light years to measure the distance of stars
A light-year is the distance that light travels in a vacuum in a year
Proxima Centauri, is the closest star to the sun.
Measuring_Distance_in_Space__The_Light_Year

3. Parallax
Astronomers have developed various methods of determining the distance of stars.
The change in position of an object with respect to a distant background is called parallax.
As Earth moves in its orbit, astronomers are able to observe stars from two different positions.
Astronomers measure the parallax of nearby stars to determine their distance from Earth

4. Properties of Stars The_Color_of_Stars
Astronomers classify stars by their color, size, and brightness. Other properties of stars are chemical composition and mass.
Color and Temperature – a stars color indicates the temperature of its’ surface.
The hottest stars appear blue
The cooler stars appear red
The spectrum of color in a star is from blues to greens to yellows and reds.
The_Color_of_Stars

5. Brightness
The brightness of a star as viewed from Earth is dependent on many factors such as color intensity and distance.
Apparent Brightness – is the brightness of a star as it appears from Earth.
The apparent brightness decreases as its distance from you increases
Absolute Brightness – is how bright a star really is. The absolute brightness is a characteristic of the star and is not dependent on its distance from Earth.

6. Composition Each star has its own spectrum.
Most stars have a chemical makeup that is similar to the sun, with hydrogen and helium together making up to 96 to 99.9 % of a star’s mass.

7. How Stars Form How_Stars_Form
A nebula is a large cloud of gas and dust spread out over a large volume of space.
Some nebulas are glowing clouds lit from within by bright stars.
A star is formed when a contacting cloud of gas and dust becomes so dense and hot that nuclear fusion begins.
How_Stars_Form

8. Life Cycles of Stars The_Life_Cycle_of_Stars.asf
Adult Stars – A star’s mass determines the star’s place on the main sequence and how long it will stay.
The amount of gas and dust available when a star forms determines the mass of each young star.
The larger the star the more energy produce.
Since blue stars burn brightly, they use up their fuel quickly and are short lived.
The_Life_Cycle_of_Stars.asf

9. The Death of a Star
The dwindling supply of fuel in a star’s core leads to the star’s death as a white dwarf, neutron star, or black hole.
Dying_Stars_and_Conclusion.asf

10. Groups of Stars
Astronomers have determined that more than half of all stars are members of star systems.
There are three basic kinds of star clusters: open clusters, associations, and globular clusters.
Astronomers classify galaxies into four main types: spiral, barred-spiral, elliptical, and irregular.

11. Expanding Universe Beyond_the_Milky_Way_and_Back_Into_Time.asf
The observed red shift in the spectra of galaxies shows that the universe is expanding.
Astronomers theorize that the universe came into being in an event called the big bang.
Dark matter can only be detected by observing its gravitational effects on visible matter.
Beyond_the_Milky_Way_and_Back_Into_Time.asf
Spin_Around_the_Solar_System__A__Look_to_the_Stars