Stars Characteristics 1/1/2019

What are the characteristics of a star? Stars differ in… Mass Size Temperature Color Luminosity

Mass and Composition A star is a massive ball of glowing gases, mainly hydrogen and helium. Bigger stars have more mass, greater gravity and are hotter than smaller stars.

Star Size Large Stars: Giants or Super Giants Medium Stars: Main Sequence (the Sun) Small Stars: White Dwarf or Neutron 1/1/2019

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Star Energy The enormous pressure and heat in a star’s core converts matter into energy. This reaction is called nuclear fusion In nuclear fusion, hydrogen atoms fuse to form helium atoms. During each step of the process, mass is lost and energy is released.

Star Energy cont. The energy released causes the star (Sun) to shine and gives the star its high temperature. 1/1/2019

Star Temperature Stars in the sky show tinges of different colors which reveal the stars’ temperatures. Blue: hottest Yellow: medium temperature Red: coolest 1/1/2019

Classification of Stars Color Surface temp (ºC) Examples Spectral Class Blue Above 30,000 10 Lacertae O Blue-white 10,000 – 30,000 Rigel, Spica B White 7,500 – 10,000 Vegas, Sirius A Yellow-white 6,000 – 7,500 Canopus, Procyon F Yellow 5,000 – 6,000 Sun, Capella G Orange 3,500 – 5,000 Arcturus, Aldebaran K Red Less than 3,500 Betelgeuse, Antares M 1/1/2019

Star Luminosity/Brightness The brightness of a star depends upon the distance and its luminosity. Apparent Brightness/Magnitude: a star’s brightness as seen from Earth. Absolute Brightness/Luminosity: the actual brightness of the star. 1/1/2019

Stop and Think If person A has a pen flashlight and person B has a mega flashlight and both were standing at the front of the classroom, which light would appear brighter? If person A (pen light) stood in the classroom and person B (mega light) stood at the baseball fields across the street, which light would appear brighter? You cannot tell by looking in the sky how bright a star truly is. The farther away the star is, the less bright it will appear. 1/1/2019

The Hertzsprung-Russell Diagram An H-R diagram plots stars according to their luminosity and temperature. 1/1/2019

Location of Stars on an H-R Diagram The main sequence is a major grouping of stars in the H-R Diagram 1/1/2019

Star Mass Position on H-R depends on mass The larger the amount of mass in a star, the more luminous it is. Giants: more mass, more luminous Dwarfs: less mass, less luminous During its lifetime a star will evolve on the H-R diagram depending on its mass. 1/1/2019