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What would happen if the sun disappeared?
+If the sun disappeared…
https://www.youtube.com/watch?feature=player_detailpage&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 1014 – 7.5 x 1014 Hz
All EM waves travel at the speed of light (3.0 x 108 m/s)
+
Stars
+Star Clusters
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
9.461 x 1012 km
Parsec (pc) 3.261 light-years
3.086 x 1013 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
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 1026 W This is equivalent to 3.85 x 1024
(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
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
Click icon to add picture
Click icon to add picture
+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 1.5-3 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
