Parallax Earth s orbit The apparent positions of nearby stars shift when viewed from different positions in H R diagram Stellar parallax used to determine a stars distance from earth d 1 p d is distance in pc Largest parallax angle smallest distance A plot of luminosity v temperature for many different stars Luminosity of Y axis Temperature on X axis On average temperature increases with luminosity Main sequence 90 of stars Like our sun stars are fusing H into He In equilibrium stable Mass and lifetime vary along the sequence Mass is directly proportional to luminosity and temperature Mass is inversely proportional to lifetime Star clusters Group of stars that is bound together by gravity 100 106 stars much smaller than a galaxy Age units of star clusters Myr 106 years or Gyr Two types of star clusters Open star clusters Loosely bound Young Small Globular star clusters Tightly bound Old Big Characteristics of star clusters sequence Spectroscopy composition and motion 3 Basic types of spectrum Continuous All stars in a cluster are the same distance from earth All stars are formed at the same time so they are the same age When a cluster forms it has stars along the whole main sequence All different masses initially before any die Stars maintain the same position on the main sequence until they die Temperature and luminosity don t change while they are still on the main The study of the constituent colors of light Spectroscopy can reveal information about an object s temperature chemical Emission Absorption Continuous No sharp spikes on graph smooth line A continuous spectrum is composed of all colors Aka thermal or blackbody Comes from dense opaque material e g solids or dense gas Hotter brighter at all Hotter bluer peaks at smaller Tells us temperature T Where it peaks shifts left on the graph peaks at smaller as it gets hotter Dimmer and redder when temperature is cooler The color of a star depends on its Surface temperature Wiens Law Relates at which spectrum peaks and temperature in kelvins peak 0029mk T Longer wavelength light often not always penetrates material better Atoms absorb or emit colors Individual The Doppler Effect A distortion of waves caused by motion Faster motion more shift Redshift Blueshift Spectral lines Waves stretched to longer redder wavelengths Happens when source OR observer moving away Waves compressed to shorter bluer wavelengths Happens when source OR observer moving toward Gravity Always pulls Acts between objects with mass Law of gravity To calculate strength of force between 2 objects F m1 x m2 d2 D is distance between objects Weaker for larger distances Stronger for larger masses Exoplanets A k a Extrasolar planets Planets orbiting other stars not our Sun Bright or dark lines that appear in an objects spectrum which we can see when we pass the objects light through a prism The faster an object rotates the wider its spectral lines will appear Very difficult to see directly Methods of indirectly detecting exoplanets 1 Doppler shift identifies wobbling stars 2 Planet transit Wobble is due to unseen planet tugging on it Planet briefly blocks some of the star s light Much more rare Planet Transit When planet passes directly in front of its star Planet briefly blocks some of the star s light Much more rare than detection with Doppler shift Rare because has to have perfect alignment and be at just the right time How often does a transit occur once per orbit for a particular planet Once per orbit Doppler Shift and stellar wobble Doppler shift identifies wobbling stars Stellar wobble is due to unseen planet tugging on it caused by force of gravity as stars and planets gravitationally tug each other F is stronger for larger masses and smaller distances Exoplanets easiest to detect are More massive planets Smaller orbits The orbital period of an exoplanet is the same as the orbital period of the stars wobble Conditions to detect no Doppler shift even when there is an exoplanet orbiting it System is seen face on inclination 0o Planet has very low mass Planet is very far from star Velocity in Doppler shift Positive velocity is away from observer Negative velocity is toward the observer Zero velocity means no Doppler shift is detected Star Formation Theory Where Stars are born in dark cold dense dusty clouds These have the right conditions and raw materials for star formation Often we can t see newborn stars b c they re deep within dark clouds However We can see the newborn star because of Infrared light Different types of light penetrate differently Stars and planets form together from a cloud that flattens and spins as it collapses Star Formation Theory How Steps stages of formation 1 Dark cloud 2 Gravitational collapse 3 Protostar 4 T tauri Star 5 Pre main sequence star 6 Young stellar system Protostar Precursor to a star but still forming Changes in cloud properties in step 1 black cloud Luminosity increases and temperature increases Gets hotter and brighter because contraction increases thermal energy As a star forms its properties change 1 Changes in cloud properties in step 1 black cloud Luminosity increases and temperature increases Gets hotter and brighter because contraction increases thermal energy 2 Cloud collapses 3 Protostar shrinks heats up 4 Fusion begins in the core Temperature still going up at this stage even though luminosity isn t Real star becomes stable gravitational equilibrium begins Main Sequence life Properties become stable and stop collapsing when there is an energy source in the core When it has nuclear fusion it is a real star Binary Stars When two stars are orbiting one another Can measure stellar masses Stars gravitationally tug on each other Low mass star stellar life Red giant Planetary Nebula White dwarf Red Giant Planetary nebula into space A low mass main sequence star becomes a red giant shell of nuclear fusion surrounding a shrinking hot core Comes from a low mass star when red giants gently cast off their outer layers of gas After a planetary nebula is a white dwarf Not as bright as a supernova Expands slower than a supernova White dwarfs End state of a low mass star Core of carbon left behind after planetary nebula takes outer layers away The density of a white dwarf is far greater than Earth or Sun Mass 1mo units of solar mass About same size as earth If not left alone can become nova or supernova High mass star stellar life Red supergiant Supernova Neutron star or black hole Red Supergiant High mass star with many