StarryM 0511

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Information about StarryM 0511

Published on November 13, 2007

Author: Gabrielle


Starry Monday at Otterbein:  Starry Monday at Otterbein Astronomy Lecture Series -every first Monday of the month- November 7, 2005 Dr. Uwe Trittmann Welcome to Today’s Topics:  Today’s Topics Classification of Stars The Night Sky in November Feedback!:  Feedback! Please write down suggestions/your interests on the note pads provided If you would like to hear from us, please leave your email / address To learn more about astronomy and physics at Otterbein, please visit (Obs.) (Physics Dept.) Classification of Stars:  Classification of Stars We can classify stars by many categories Name Position Constellation Distance Color Temperature Size Brightness Spectra Features: double stars, variable stars, … How Stars Got Their Names:  How Stars Got Their Names Some have names that go back to ancient times (e.g. Castor and Pollux, Greek mythology) Some were named by Arab astronomers (e.g. Aldebaran, Algol, etc.) Since the 17th century we use a scheme that lists stars by constellation in order of their apparent brightness labeled alphabetically in Greek alphabet Alpha Centauri is the brightest star in constellation Centaurus Some dim stars have names according to their place in a catalogue (e.g. Ross 154) Positions of Stars :  Positions of Stars The Celestial Sphere An imaginary sphere surrounding the earth, on which we picture the stars attached Axis through earth’s north and south pole goes through celestial north and south pole Earth’s equator Celestial equator Celestial Coordinates:  Celestial Coordinates Earth: latitude, longitude Sky: declination (dec) [from equator,+/-90°] right ascension (RA) [from vernal equinox, 0-24h; 6h=90°] Examples: Westerville, OH 40.1°N, 88°W Betelgeuse (α Orionis) dec = 7° 24’ RA = 5h 52m But: What’s up for you…:  But: What’s up for you… Observer Coordinates Horizon – the plane you stand on Zenith – the point right above you Meridian – the line from North to Zenith to south …depends where you are!:  …depends where you are! Your local sky – your view depends on your location on earth Constellations of Stars:  Constellations of Stars About 5000 stars visible with naked eye About 3500 of them from the northern hemisphere Stars that appear to be close are grouped together into constellations since antiquity Officially 88 constellations (with strict boundaries for classification of objects) Names range from mythological (Perseus, Cassiopeia) to technical (Air Pump, Compass) Constellations of Stars (cont’d):  Constellations of Stars (cont’d) Orion as seen at night Orion as imagined by men Constellations (cont’d):  Constellations (cont’d) Orion “from the side” Stars in a constellation are not connected in any real way; they aren’t even close together! Distances to the Stars:  Distances to the Stars Parallax can be used out to about 100 light years The parsec: Distance in parsecs = 1/parallax (in arc seconds) Thus a star with a measured parallax of 1” is 1 parsec away 1 pc is about 3.3 light years The nearest star (Proxima Centauri) is about 1.3 pc or 4.3 lyr away Solar system is less than 1/1000 lyr Our Stellar Neighborhood:  Our Stellar Neighborhood Scale Model:  Scale Model If the Sun = a golf ball, then Earth = a grain of sand The Earth orbits the Sun at a distance of one meter Proxima Centauri lies 270 kilometers (170 miles) away Barnard’s Star lies 370 kilometers (230 miles) away Less than 100 stars lie within 1000 kilometers (600 miles) The Universe is almost empty! Hipparcos satellite measured distances to nearly 1 million stars in the range of 100 pc almost all of the stars in our Galaxy are more distant Brightness:  Brightness A measure of the apparent brightness Logarithmic scale Notation: 1m.4 (smaller brighter) Originally six groupings 1st magnitude the brightest 6th magnitude the dimmest The modern scale is more complex The absolute magnitude is the apparent magnitude a star would have at a distance of 10 pc: 2M.8 Electromagnetic Spectrum:  Electromagnetic Spectrum Three Things Light Tells Us:  Three Things Light Tells Us Temperature from black body spectrum Chemical composition from spectral lines Radial velocity from Doppler shift Black Body Spectrum (gives away the temperature):  Black Body Spectrum (gives away the temperature) All objects - even you - emit radiation of all frequencies, but with different intensities Peak frequency Measuring Temperatures:  Measuring Temperatures Find maximal intensity  Temperature (Wien’s law) Identify spectral lines of ionized elements  Temperature Wien’s Law:  Wien’s Law The peak of the intensity curve will move with temperature, this is Wien’s law: λ T = const. = 0.0029 m · K So: the higher the temperature T, the smaller the wavelength λ, i.e. the higher the energy of the electromagnetic wave Luminosity and Brightness:  Luminosity and Brightness Luminosity L is the total power (energy per unit time) radiated by the star Apparent brightness B is how bright it appears from Earth Determined by the amount of light per unit area reaching Earth B  L / d2 Just by looking, we cannot tell if a star is close and dim or far away and bright Measuring the Sizes of Stars:  Measuring the Sizes of Stars Direct measurement is possible for a few dozen relatively close, large stars Angular size of the disk and known distance can be used to deduce diameter Sizes of Stars:  Sizes of Stars Dwarfs Comparable in size, or smaller than, the Sun Giants Up to 100 times the size of the Sun Supergiants Up to 1000 times the size of the Sun Note: Temperature changes! Star Systems: Binary Stars:  Star Systems: Binary Stars Some stars form binary systems – stars that orbit one another visual binaries spectroscopic binaries eclipsing binaries Beware of optical doubles stars that happen to lie along the same line of sight from Earth We can’t determine the mass of an isolated star, but of a binary star Visual Binaries:  Visual Binaries Members are well separated, distinguishable Spectroscopic Binaries:  Spectroscopic Binaries Too distant to resolve the individual stars Can be viewed indirectly by observing the back-and-forth Doppler shifts of their spectral lines Eclipsing Binaries (Rare!):  Eclipsing Binaries (Rare!) The orbital plane of the pair almost edge-on to our line of sight We observe periodic changes in the starlight as one member of the binary passes in front of the other Spectral Classification of the Stars:  Spectral Classification of the Stars Class Temperature Color Examples O 30,000 K blue B 20,000 K bluish Rigel A 10,000 K white Vega, Sirius F 8,000 K white Canopus G 6,000 K yellow Sun,  Centauri K 4,000 K orange Arcturus M 3,000 K red Betelgeuse Mnemotechnique: Oh, Be A Fine Girl/Guy, Kiss Me Spectral Lines – Fingerprints of the Elements:  Spectral Lines – Fingerprints of the Elements Can use spectra to identify elements on distant objects! Different elements yield different emission spectra Origin of Spectral Lines:  Origin of Spectral Lines Atoms: electrons orbiting nuclei Chemistry deals only with electron orbits (electron exchange glues atoms together to from molecules) Nuclear power comes from the nucleus Nuclei are very small If electrons would orbit the statehouse on I-270, the nucleus would be a soccer ball in Gov. Bob Taft’s office Nuclei: made out of protons (el. positive) and neutrons (neutral) Slide32:  The energy of the electron depends on orbit When an electron jumps from one orbital to another, it emits (emission line) or absorbs (absorption line) a photon of a certain energy The frequency of emitted or absorbed photon is related to its energy E = h f (h is called Planck’s constant, f is frequency) Hertzsprung-Russell-Diagram:  Hertzsprung-Russell-Diagram Hertzsprung-Russell diagram is luminosity vs. spectral type (or temperature) To obtain a HR diagram: get the luminosity. This is your y-coordinate. Then take the spectral type as your x-coordinate. This may look strange, e.g. K5III for Aldebaran. Ignore the roman numbers ( III means a giant star, V means dwarf star, etc). First letter is the spectral type: K (one of OBAFGKM), the arab number (5) is like a second digit to the spectral type, so K0 is very close to G, K9 is very close to M. Constructing a HR-Diagram:  Constructing a HR-Diagram Example: Aldebaran, spectral type K5III, luminosity = 160 times that of the Sun O B A F G K M Type … 0123456789 0123456789 012345… 1 10 100 1000 L Aldebaran Sun (G2V) 160 The Hertzprung-Russell Diagram:  The Hertzprung-Russell Diagram A plot of absolute luminosity (vertical scale) against spectral type or temperature (horizontal scale) Most stars (90%) lie in a band known as the Main Sequence Hertzsprung-Russell diagrams:  Hertzsprung-Russell diagrams … of the closest stars …of the brightest stars Mass and the Main Sequence:  Mass and the Main Sequence The position of a star in the main sequence is determined by its mass All we need to know to predict luminosity and temperature! Both radius and luminosity increase with mass Stellar Lifetimes:  Stellar Lifetimes From the luminosity, we can determine the rate of energy release, and thus rate of fuel consumption Given the mass (amount of fuel to burn) we can obtain the lifetime Large hot blue stars: ~ 20 million years The Sun: 10 billion years Small cool red dwarfs: trillions of years The hotter, the shorter the life! Preview: Stellar Lifecycle:  Preview: Stellar Lifecycle Next Starry Monday: How stars are born and die What makes stars “shine” Planetary nebulae are dead stars! …and much more The Night Sky in November:  The Night Sky in November Back to standard time -> earlier observing! Autumn constellations are up: Cassiopeia, Pegasus, Perseus, Andromeda, Pisces  lots of open star clusters! Mars at opposition Saturn is visible later at night Moon Phases:  Moon Phases Today (New Moon, 36%) 11 / 8 (First Quarter Moon) 11 / 15 (Full Moon) 11 / 23 (Last Quarter Moon) 12/ 1 (New Moon) Today at Noon:  Today at Noon Sun at meridian, i.e. exactly south 10 PM:  10 PM Typical observing hour, early November Mars Uranus at meridian Neptune Moon South-East:  South-East Plejades Mars at its brightest in Aries West:  West The summer triangle is still hanging on … Due North:  Due North Big Dipper points to the north pole High up – the Autumn Constellations:  High up – the Autumn Constellations W of Cassiopeia Big Square of Pegasus Andromeda Galaxy Andromeda Galaxy:  Andromeda Galaxy “PR” Foto Actual look South-East:  South-East High in the sky: Perseus and Auriga with Plejades and the Double Cluster South-West:  South-West Planets Uranus Neptune Zodiac: Capricorn Aquarius Mark your Calendars! :  Mark your Calendars! Next Starry Monday: January 9, 2005, 7 pm (this is a Monday ) Observing at Prairie Oaks Metro Park: Friday, November 18, 7:30 pm Web pages: (Obs.) (Physics Dept.) Mark your Calendars II :  Mark your Calendars II Physics Coffee is every Wednesday, 3:30 pm Open to the public, everyone welcome! Location: across the hall, Science 256 Free coffee, cookies, etc. It’s Nuclear Fusion !:  It’s Nuclear Fusion ! Atoms: electrons orbiting nuclei Chemistry deals only with electron orbits (electron exchange glues atoms together to from molecules) Nuclear power comes from the nucleus Nuclei are very small If electrons would orbit the statehouse on I-270, the nucleus would be a soccer ball in Gov. Bob Taft’s office Nuclei: made out of protons (el. positive) and neutrons (neutral) Nuclear fusion reaction:  Nuclear fusion reaction Further Reactions – Heavier Elements:  Further Reactions – Heavier Elements Could We Use This on Earth?:  Could We Use This on Earth? Requirements: High temperature High density Very difficult to achieve on Earth! Nuclear Fission:  Nuclear Fission Problems: limited fuel supply, dangerous byproducts, expensive technology, limited lifetime of power plant due to radiation The Solar Neutrino Problem:  The Solar Neutrino Problem We can detect the neutrinos coming from the fusion reaction at the core of the Sun The results are 1/3 to 1/2 the predicted value! Possible explanations: Models of the solar interior are incorrect Our understanding of the physics of neutrinos is incorrect Something is horribly, horribly wrong with the Sun #2 is the answer – neutrinos “oscillate” Homework: Luminosity and Distance:  Homework: Luminosity and Distance Distance and brightness can be used to find the luminosity: L  d2 B So luminosity and brightness can be used to find Distance of two stars 1 and 2: d21 / d22 = L1 / L2 (since B1 = B2 ) Stars II - Lifecycle:  Stars II - Lifecycle The Fundamental Problem:  The Fundamental Problem We study the subjects of our research for a tiny fraction of its lifetime Sun’s life expectancy ~ 10 billion (1010) years Careful study of the Sun ~ 370 years We have studied the Sun for only 1/27 millionth of its lifetime! Suppose we study human beings…:  Suppose we study human beings… Human life expectancy ~ 75 years 1/27 millionth of this is about 74 seconds What can we learn about people when allowed to observe them for no more than 74 seconds? Star Formation:  Star Formation A star’s existence is based on a competition between gravity (inward) and pressure due to energy production (outward) Stage 1: Contraction of a cold interstellar cloud Lasts about 2 million years Central temperature about 10 K Size ~ tens of parsecs Star Formation (cont’d):  Star Formation (cont’d) Stage 2: Cloud contracts/warms, begins radiating; almost all radiated energy escapes Duration ~ 30,000 years Temperature ~ 100 K at center, 10 K at surface Size about 100 times that of the solar system Stage 3: Cloud becomes dense  opaque to radiation  radiated energy trapped  core heats up Duration ~ 100,000 years Temperature ~ 10,000 K at center, 100 K at surface Size ~ the solar system Example: Orion Nebula :  Example: Orion Nebula Orion Nebula is a place where stars are being born Orion Nebula (M42):  Orion Nebula (M42) Protostellar Evolution:  Protostellar Evolution Stage 4: increasing temperature at core slows contraction Luminosity about 1000 times that of the sun Duration ~ 1 million years Temperature ~ 1 million K at core, 3,000 K at surface Still too cool for nuclear fusion! Size ~ orbit of Mercury The T Tauri Stage:  The T Tauri Stage Stage 5 (T Tauri): Violent surface activity high solar wind blows out the remaining stellar nebula Duration ~ 10 million years Temperature ~ 5106 K at core, 4000 K at surface Still too low for nuclear fusion Luminosity drops to about 10  the Sun Size ~ 10  the Sun Possible T Tauri Stars:  Possible T Tauri Stars Jets from T Tauri Stars:  Jets from T Tauri Stars Path in the Hertzsprung-Russell Diagram:  Path in the Hertzsprung-Russell Diagram Stages 1-5 Observational Confirmation:  Observational Confirmation Preceding the result of theory and computer modeling Can observe objects in various stages of development, but not the development itself A Newborn Star:  A Newborn Star Stage 6: Temperature and density at core high enough to sustain nuclear fusion Duration ~ 30 million years Temperature ~ 10 million K at core, 4500 K at surface Size ~ slightly larger than the Sun Stage 7: Main-sequence star; pressure from nuclear fusion and gravity are in balance Duration ~ 10 billion years (much longer than all other stages combined) Temperature ~ 15 million K at core, 6000 K at surface Size ~ Sun Path in the Hertzsprung-Russell Diagram:  Path in the Hertzsprung-Russell Diagram The new-born stars ‘hops’ onto the main sequence Mass Matters:  Mass Matters Larger masses higher surface temperatures higher luminosities take less time to form have shorter main sequence lifetimes Smaller masses lower surface temperatures lower luminosities take longer to form have longer main sequence lifetimes Failed Stars: Brown Dwarfs:  Failed Stars: Brown Dwarfs Too small for nuclear fusion to ever begin Less than about 0.08 solar masses Give off heat from gravitational collapse Luminosity ~ a few millionths that of the Sun Main Sequence Lifetimes:  Main Sequence Lifetimes Mass (in solar masses) Luminosity Lifetime 10 Suns 10,000 Suns 10 Million yrs 4 Suns 100 Suns 2 Billion yrs 1 Sun 1 Sun 10 Billion yrs ½ Sun 0.01 Sun 500 Billion yrs Why Do Stars Leave the Main Sequence?:  Why Do Stars Leave the Main Sequence? Running out of fuel Stage 8: Hydrogen Shell Burning:  Stage 8: Hydrogen Shell Burning Cooler core  imbalance between pressure and gravity  core shrinks hydrogen shell generates energy too fast  outer layers heat up  star expands Luminosity increases Duration ~ 100 million years Temperature ~ 50 million K (core) to 4000 K (surface) Size ~ several Suns Stage 9: The Red Giant Stage:  Stage 9: The Red Giant Stage Luminosity huge (~ 100 Suns) Core contains 25% of the star’s mass and continues to shrink Strong stellar winds eject up to 30% of stars mass from surface Duration: 100,000 years Temperature: 100  106 K (core) to 4000 K (surface) Size ~ 70 Suns (orbit of Mercury) Lifecycle :  Lifecycle Lifecycle of a main sequence G star The Helium Flash and Stage 10:  The Helium Flash and Stage 10 The core becomes hot and dense enough to overcome the barrier to fusing helium into carbon Initial explosion followed by steady (but rapid) fusion of helium into carbon Lasts: 50 million years Temperature: 200 million K (core) to 5000 K (surface) Size ~ 10  the Sun Stage 11:  Stage 11 Helium burning continues Carbon “ash” at the core forms, and the star becomes a Red Supergiant Duration: 10 thousand years Central Temperature: 250 million K Size > orbit of Mars Stage 12:  Stage 12 Inner carbon core becomes “dead” – it is out of fuel Some helium and carbon burning continues in outer shells The outer envelope of the star becomes cool enough for atoms to recombine with electrons, and becomes opaque; solar radiation pushes it outward from the star A planetary nebula is formed Duration: 100,000 years Central Temperature: 300  106 K Surface Temperature: 100,000 K Size: 0.1  Sun Planetary Nebulae:  Planetary Nebulae “Eye of God” Nebula Slide86:  “Cat’s Eye” Nebula Slide87:  “Wings of the Butterfly” Nebula Slide88:  The Ring Nebula (M57) Slide89:  “Eskimo” Nebula Slide90:  “Stingray” Nebula Slide91:  “Ant” Nebula Stage 13: White Dwarf:  Stage 13: White Dwarf Core radiates only by stored heat, not by nuclear reactions core continues to cool and contract Temperature: 100  106 K at core; 50,000 K at surface Size ~ Earth Density: a million times that of Earth – 1 cubic cm has 1000 kg of mass! Stage 14: Black Dwarf:  Stage 14: Black Dwarf Impossible to see in a telescope About the size of Earth Temperature very low  almost no radiation  black! Evolution of More Massive Stars:  Evolution of More Massive Stars Gravity is strong enough to overcome the electron pressure (Pauli Exclusion Principle) at the end of the helium-burning stage The core contracts until its temperature is high enough to fuse carbon into oxygen Elements consumed in core new elements form while previous elements continue to burn in outer layers Evolution of More Massive Stars:  Evolution of More Massive Stars At each stage the temperature increases  reaction gets faster Last stage: fusion of iron does not release energy, it absorbs energy  cools the core  “fire extinguisher” Neutron Core:  Neutron Core The core cools and shrinks nuclei and electrons are crushed together protons combine with electrons to form neutrons Ultimately the collapse is halted by neutron pressure Most of the core is composed of neutrons at this point Size ~ few km Density ~ 1018 kg/m3; 1 cubic cm has a mass of 100 million kg! Manhattan Formation of the Elements:  Formation of the Elements Light elements (hydrogen, helium) formed in Big Bang Heavier elements formed by nuclear fusion in stars and thrown into space by supernovae Condense into new stars and planets Elements heavier than iron form during supernovae explosions Evidence: Theory predicts the observed elemental abundance in the universe very well Spectra of supernovae show the presence of unstable isotopes like Nickel-56 Older globular clusters are deficient in heavy elements Slide98:  Review: The life of Stars

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