Stars
Dec 15, 2015
Stars
Distances To The Stars
• 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
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
Properties 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
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.
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.
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
Life Cycles of Stars
• 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
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
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.
Expanding Universe
• 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