Definitions  Sun: Star at the center of our solar system. Also another name for any star.  Luminosity: measures how bright a star would be in relation to the sun if all stars were the same distance from the observer

 Nuclear fusion: the combining of the nuclei of smaller elements to form the nuclei of larger elements with some mass being converted into energy- this is how the sun produces energy  The color of a star is determined by the temperature of the star- blue is the hottest and red is the coolest

Definitions  Sunspots: a darker region of the sun’s visible surface; increased number of sunspots are related to an increase in electromagnetic energy emitted from the sun. Cycle is about 11 years in length

Photosphere with Sun Spots

Stefan-Boltzmann Law (Energy directly proportional to temperature)  Our sun burns “slowly” 9 billion years total (4.5 billions years left to go!)  Stefan-Boltzmann Chart: Organizes stars by size, temperature and luminosity

Development of Stars  Stars may follow different paths in this cycle  Life cycle may take billions of years  Some stars created soon after the Big Bang may still exist

Nebula a. a huge, spread out cloud of gas and dust in space. b. The gas in nebulae is mostly hydrogen gas c. Ingredients needed for star formation

Main Sequence/Average Star a. Main sequence stars are the central band of stars on the star diagram. b. Energy comes from nuclear fusion as they convert Hydrogen to Helium. c. The sun is a typical Main Sequence star. d. Most stars (about 90%) are Main Sequence Stars. e. For these stars, the hotter, the brighter

Giant Stars a. Rare red, orange, and yellow stars commonly seen at night because of their large size and high luminosity b. Low temperature stars c. Represent the late stage in the evolution of medium to small-size main sequence stars

Planetary Nebula  nebula formed by a shell of gas which was sent out from a certain kind of a red giant or supergiant.  As the giant star explodes, the core of the star is exposed.  Planetary nebulae have nothing to do with planets.

White Dwarfs a. Not always white b. Small (around the size of Earth) c. Hot on the surface, low in luminosity d. Represent last stage of low to medium mass stars

Black Dwarf a. When a white dwarf cools and no longer emits much electromagnetic energy b. “Dead” star

Other Path: Super Giants a. Super giant stars can be up to 1000 times larger than the diameter of the sun b. Late stage of evolution c. Usually explode in a supernova d. Blue super giants are the brightest and exhibit the highest temperature

Supernova a. the explosion of most of the material in a star, resulting in an extremely bright, short-lived object that emits vast amounts of energy. b. Occurs when nuclear fuel is exhausted so the star can no longer support itself through fusion

Black Hole  An area of space with a gravitational field so intense that its escape velocity is equal to or exceeds the speed of light- results from supernova

Neutron Stars  A celestial body consisting of the dense remains of a massive star that has collapsed, thus leaving only neutrons, and having a powerful gravitational attraction

Movies  Life Cycle of Stars Life Cycle of Stars  Another Video of Life Cycle Another Video of Life Cycle