2Distances 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 starsA light-year is the distance that light travels in a vacuum in a yearProxima Centauri, is the closest star to the sun.Measuring_Distance_in_Space__The_Light_Year
3ParallaxAstronomers 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
4Properties 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 blueThe cooler stars appear redThe spectrum of color in a star is from blues to greens to yellows and reds.The_Color_of_Stars
5BrightnessThe 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 increasesAbsolute 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.
6Composition 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.
7How 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
8Life 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
9The Death of a StarThe 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
10Groups of StarsAstronomers 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.
11Expanding 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.asfSpin_Around_the_Solar_System__A__Look_to_the_Stars