Our Sun: an average size star Stars & The Sun  The Life Cycle of a Star: Stars have a life cycle and evolve over time. The mass of a star controls its: Evolution Lifespan Ultimate fate (how it dies) Our Sun: an average size star

Stars begin as a nebula (cloud of gas and dust) that starts to contract due to gravity. Protostar: temperature increases, millions of years later the gas becomes plasma and nuclear fusion begins. Main sequence star: (the longest stage in the life of a star) nuclear fusion (hydrogen fuses into helium) continues in the core of the star...our Sun is a main sequence star. Balancing Act

Stars more massive than our Sun may be main sequence stars for only 10 million years Stars less massive than our Sun may be main sequence stars for 100’s of billions of years Remember: the larger the star the shorter the life span, the smaller the star the longer the life span

Path of a star much larger than our sun A star starts to die when hydrogen runs low: Giant: A star cools as it expands and starts to glow red. Giants can be more than 10 times larger than the sun. White dwarf: outer layers escape into space, the star collapses into a dense hot, dim star smaller than Earth. Path of a star much larger than our sun Path of our Sun

Massive Stars die explosively!! 6.Supergiant: Massive stars become larger than giants as they leave the main sequence….they can be 100 to 1,000 times larger than the sun. 7.Supernova: the explosion of a supergiant Neutron Star: a small dense ball of neutrons that spin after a supernova explosion Black Hole: the remnants of a supernova that are contracted even more than a neutron star… it is so dense light cannot escape from it.

Can you spot the supernova? These are before-and-after images of a recent supernova event (Supernova 2005cs) in the galaxy M51. Can you spot the bright supernova in the after (right) that wasn’t visible before? Images used with permission. ©2005-2007 by R. Jay GaBany http://www.cosmotography.com

ultraviolet-light exposure Are Black Holes Important? Every spiral galaxy, like our own Milky Way, is thought to have a supermassive black hole at its center. The black hole at the center of the Milky Way is sort of like the Sun at the center of our solar system - the galaxy orbits the black holes like the planets in solar systems orbit the stars. ultraviolet-light exposure Black Hole Swallows a Star These images, taken with NASA's Galaxy Evolution Explorer and the Pan-STARRS1 telescope in Hawaii, show a brightening inside a galaxy caused by a flare from its nucleus. The arrow in each image points to the galaxy. The flare is a signature of the galaxy's central black hole shredding a star that wandered too close. The top left image, taken by the Galaxy Evolution Explorer in 2009, shows the galaxy's location before the flare. The galaxy is not visible in this ultraviolet-light exposure. In the top right image, taken by the Galaxy Evolution Explorer on June 23, 2010, the galaxy has become 350 times brighter in ultraviolet light. The bottom left image, taken by Pan-STARRS1, shows the galaxy (the bright dot in the center) in 2009 before the flare's appearance. The bottom right image, taken by Pan-STARRS1 from June to August 2010, shows the flare from the galaxy nucleus. Note how the light from the flare is much bluer, or hotter, than the host galaxy light.

Composition of Universe Massive Stars are important because….. During the fusion process of hotter massive stars, elements such as iron, oxygen, silicon and magnesium are created. These are elements needed for life. Composition of Universe

Magnitude describes the brightness of a star Two types of brightness: absolute magnitude and apparent magnitude Apparent magnitude is the brightness we see here on Earth Absolute magnitude is the actual brightness the star gives off. The more negative the number, the brighter the star is!

ORION CONSTELLATION Betelgeuse Rigel Rigel

Parallax is a method used to determine distance to a star. To figure out how far it is to a star, astronomers look at it from two different positions, called parallax Parallax is a method used to determine distance to a star.

STARS ARE CLASSIFIED BY THEIR SIZE, COLOR AND TEMPERATURE Not all stars are the same color because different elements burn different colors. Some are red, some are blue, etc. Color tells the temperature of the star Hot stars are bluish/white and cooler stars are reddish/orange Astronomers call this a star’s spectral class. Spectral classes are O, B, A, F, G, K, and M Flame Test Clip

Hertzsprung-Russell Diagram (H-R Diagram) Stars are ranked on the H-R Diagram based on their temperature and absolute magnitude Most stars fall in the middle of the diagram, called the main sequence Very few stars are white dwarfs or giants/supergiants

H-R Diagram---shows the life cycle of stars supergiants Main sequence giants Absolute magnitude White dwarfs temperature

Constellations Constellations are patterns of stars in the night sky, commonly named after animals and characters in Greek mythology Currently there are 88 that are named If you look in the direction of north, there are constellations that appear to move in a circle around the North Star, Polaris. These are circumpolar constellations. They are visible year-round in each hemisphere