+ Quick write What would happen if the sun disappeared?

+ If the sun disappeared… &v=rltpH6ck2Kc &v=rltpH6ck2Kc

+ Electromagnetic Spectrum

+ Light? What is light? What do we see it as?

+ Electromagnetic Radiation Electromagnetic (EM) Radiation Commonly known as “light” Electric and magnetic disturbances Travels through space as waves EM Spectrum All the different sources of EM Radiation Includes: Radio waves Microwaves Infrared waves Visible light Ultraviolet X-Rays Gamma rays

+ Electromagnetic Radiation Visible Light The limited portion of the EM Spectrum that the human eye can sense

+ The EM Spectrum

+ A little less complicated…

+ EM Spectrum Classified by wavelength Distance between peaks on a wave Red light has a longer wavelength than blue light Radio waves have longer wavelengths than gamma Can also be classified by frequency The number of waves per second Visible light frequency ranges from 4.3 x – 7.5 x Hz All EM waves travel at the speed of light (3.0 x 10 8 m/s)

+ Stars

+ Star Clusters Stars that are gravitationally bound to one another NOT a constellation Pleiades, in Taurus – open cluster - densely packed M13, in Hercules – globular cluster – densely packed

+ Binaries Binary Stars Two stars that are gravitationally bound and orbit a common center of mass More than half the stars in the sky are binaries (or multiple-star systems Sirius

+ Distance in Space Light Year (ly) The distance light travels in one year x km Parsec (pc) light-years x km

+ Properties of Stars Diameter Mass Brightness Power Surface temperature Composition

+ Magnitude Apparent Magnitude How bright a star appears to be Brighter stars are +1, next +2, etc. A difference of 5 equals a factor of 100 in brightness A +1 star is 100 times brighter than a +6 star BUT…does not actually indicate how bright a star actually is because it does not account for distance! Absolute Magnitude The brightness an object would be if it were placed at a distance of 10 pc MUST know actual star distance! More accurate system

+ Luminosity The measure of energy output from the surface of a star per second Must know apparent magnitude AND distance Measured in Watts Sun is 3.85 x W This is equivalent to 3.85 x (3,850,000,000,000,000,000,000,000) 100-W light bulbs

+ Classifying Stars (Temperature) Stars are assigned a spectral type in the following order: O, B, A, F, G, K, M These are subdivided into divisions with numbers 0-9 The classes correspond to stellar temperatures O stars are the hottest About 50,000 K M stars are the coolest As low as 2,000 K Sun is a G2 Star, which corresponds to a surface temp of 5800 K

+ Composition All stars have nearly identical composition Typically, the mass of a star is: About 73% Hydrogen About 25% Helium About 2% other elements

+ Hertzsprung-Russell Diagram A graph that shows relationship between mass, luminosity, temperature, and diameter 90% of stars are Main Sequence Stars Includes our Sun These stars run diagonally from upper-left corner (hot, luminous stars) to lower-right (cool, dim stars) Other stars Red Giants Large and cool White Dwarfs Hot, dim; size of Earth; mass of the Sun

+ Star Formation

+ Star Structure The larger the star, the more gravity Temperature inside the star dictates the rate of nuclear reactions This determines luminosity

+ Stellar Fusion Density and temperature increase toward the center At the center, energy is generated by nuclear fusion The process of fusing elements together For main sequence stars, it begins with fusing hydrogen into helium The energy produces pressure to counteract gravity

+ Star Formation Begins as a NEBULA A cloud of interstellar gas and dust Cloud collapses on itself because of own gravity Cloud contracts and rotation forces it into a disk shape Becomes a PROTOSTAR Disk-shaped, with a hot condensed object at the center Temp inside becomes hot enough for nuclear fusion to begin Hydrogen  Helium first Star becomes stable because the internal heat can produce enough pressure to counteract gravity Now truly a star Can take it’s place on the Main Sequence according to its mass

+ Stellar Life Cycle Life cycle depends on mass Sun converts hydrogen to helium. Gradually becomes more luminous Core density and temp rise Increase in reaction rate A star with a mass of the Sun takes about 10 billion years to convert all its hydrogen core into helium Once the hydrogen core is gone, star becomes RED GIANT Decrease in temp due to expansion Increase in luminosity Converts helium to carbon

+ Stellar Life Cycle After the Red Giant core is all carbon: Outer layers of star are driven off Shell of gas called PLANETARY NEBULA Sun’s mass never becomes hot enough for carbon to react Energy production ends Core becomes exposed as small, hot object called WHITE DWARF Size of earth Stable Does not require a source of heat to be maintained

+ Life Cycles of Other Stars Stars SMALLER than the Sun have LONGER lifetimes Dim and do not use energy rapidly Massive Stars Up to 8-times bigger than the Sun Same beginning Short lifetime Very luminous, uses fuel quickly Produces more elements in interior

+ Life Cycle of a Massive Star Red Giant expands at the end of each reaction stage Becomes SUPERGIANT Betelgeuse in Orion Ends as a white dwarf Can be made of oxygen, neon, etc. (not just carbon)

+ Life Cycle of a Massive Star Some stars do not lose enough mass to become a white dwarf A star beginning 8-20 times larger than Sun is too massive Comes to a violent end Reactions will create iron Then reactions stop Star violently collapses in on itself Core becomes NEUTRON STAR Mass times the Sun Radius only 10 km 100 trillion times more dense than water

+ Life Cycle of a Massive Star Outer layers of the Neutron Star still fall inward The gas rebounds after striking the hard surface of the star Explodes outward Entire outer portion of star is blown off in massive explosion, called a SUPERNOVA

+ Life Cycle of a Massive Star Some stars are too big to even form neutron stars A star that begins with 20 times the Sun’s mass will never form a neutron star The core of the star continues to collapse forever Compacts matter into smaller and smaller volume The small, but extremely dense object that remains is a BLACK HOLE Gravity is so great that nothing escapes Not even light