* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Chapter 10: Measuring the Stars - Otto
Star of Bethlehem wikipedia , lookup
Space Interferometry Mission wikipedia , lookup
Constellation wikipedia , lookup
Dyson sphere wikipedia , lookup
Theoretical astronomy wikipedia , lookup
International Ultraviolet Explorer wikipedia , lookup
Astronomical unit wikipedia , lookup
Dialogue Concerning the Two Chief World Systems wikipedia , lookup
Corona Borealis wikipedia , lookup
Canis Minor wikipedia , lookup
Observational astronomy wikipedia , lookup
Future of an expanding universe wikipedia , lookup
H II region wikipedia , lookup
Auriga (constellation) wikipedia , lookup
Aries (constellation) wikipedia , lookup
Star catalogue wikipedia , lookup
Corona Australis wikipedia , lookup
Cassiopeia (constellation) wikipedia , lookup
Timeline of astronomy wikipedia , lookup
Canis Major wikipedia , lookup
Cygnus (constellation) wikipedia , lookup
Stellar classification wikipedia , lookup
Perseus (constellation) wikipedia , lookup
Stellar evolution wikipedia , lookup
Malmquist bias wikipedia , lookup
Cosmic distance ladder wikipedia , lookup
Star formation wikipedia , lookup
Aquarius (constellation) wikipedia , lookup
Chapter 10 Measuring the Stars Star Cluster NGC 3603 20,000 light-years away Figure 10.1 Stellar Parallax Stellar parallax • Measure distance to nearest stars • Baseline is earth’s orbital diameter of 2 A.U. • Parallactic angle (or parallax) is half of total angle • Star with parallax of 1” is 1 parsec distant • 1 parsec (1 pc) is about 3.3 light-years • Smaller parallax means more distant Proxima Centauri • • • • • Part of Alpha Centauri triple star system Closest star to earth, largest parallax 0.76” parallax (difficult to measure) 1.3 pc or 4.3 light-years away About 300,000X further away than sun Figure 10.2 Sun’s Neighborhood Nearest neighbor stars • Less than 100 stars within 5 pc • Several 1000 stars within 30 pc Hipparcos satellite • Can measure out to 200 pc • Nearly a million stars • Future satellites will measure to 25,000 pc Stellar motion • Radial velocity - along line of sight • Measure using Doppler shift • Transverse velocity - perpendicular to line of sight • Monitor star’s position on sky Figure 10.3 Real Space Motion a), b) Barnard’s Star - 22 years apart c) Alpha Centauri Proper motion • • • • • Annual movement of star across sky Corrected for parallax Barnard’s star moved 227” in 22 years 10.3” per year proper motion 1.8 pc distance - transverse velocity is 88 km/s Brightness and distance • Luminosity or absolute brightness (intrinsic) • Apparent brightness is how bright star looks from earth • Apparent brightness depends on luminosity and distance Figure 10.4 Inverse-Square Law Figure 10.5 Luminosity Apparent brightness proportional to luminosity/distance2 Magnitude scale • Greek astronomer Hipparchus (2nd century BC) • Ranked stars into six groups • Brightest stars are 1st magnitude • Next brightest stars are 2nd magnitude • Faintest stars (to naked eye) are 6th magnitude • Larger magnitude means fainter star Apparent magnitude • Expanded beyond stars visible to naked eye • One magnitude difference is 2.5X in brightness • A 1st magnitude star is 2.5X brighter than a 2nd magnitude star • Full moon has an apparent magnitude of -12.5 • Faintest objects visible by Hubble or Keck telescopes are apparent magnitude 30 Figure 10.6 Apparent Magnitude Absolute magnitude • It is the apparent magnitude of a star viewed from a distance of 10 pc • Measure of absolute brightness or luminosity • Our sun has absolute magnitude of 4.8 • (If sun were 10 pc from us, its apparent magnitude would be 4.8, which is faint) More Precisely 10.1 More on the Magnitude Scale Figure 10.7 Star Colors Stellar color • Temperature of star determines blackbody curve • Measurements at two wavelengths can determine blackbody curve temperature • Use B (blue) and V (visual green/yellow) filters • Determines star’s color index or color Figure 10.8 Blackbody Curves Table 10-1 Stellar Colors and Temperatures Stellar spectra • • • • • Absorption spectrum Aborption lines determine elements Temperature determines strength of lines Hotter stars have more ionized atoms Coolest stars can have molecular lines Figure 10.9 Stellar Spectra Spectral classification • In 1800’s letter classification used for stellar spectra • Later rearranged into order of decreasing temperature Table 10.2 Spectral Classes OBAFGKM • • • • • • Highest to lowest temperature Mnemonic: Oh, Be A Fine Girl, Kiss Me Oh, Be A Fine Guy, Kiss Me Oh Beastly And Fearsome Gorilla, Kill Me (Make up your own) Spectral class subdivisions • Each letter has 10 subdivisions, 0 - 9 • 0 is hottest, 9 is coolest, within letter class • Sun is G2 (cooler than G1, hotter than G3) Direct size measurement • Several stars are large, bright and close enough to measure their size directly Figure 10.10 Betelgeuse Indirect size measurement • • • • Most stars’ sizes can’t be measured directly Use luminosity temperature4 And luminosity area (or radius2) Indirectly determines radius Figure 10.11 Stellar Sizes Stellar sizes • R - radius of sun • Giants - 10X to 100X R • Supergiants - up to 1000X R • Dwarf - comparable to or smaller than R Hertzsprung-Russell Diagram • • • • H-R diagram Each point represents a star Luminosity on vertical scale Temperature (decreasing) on horizontal scale Figure 10.12 H-R Diagram of Well-Known Stars Stellar radii and H-R diagram • Radius-luminosity-temperature relationship gives radius • Diagonal dashed lines on H-R diagrams represent constant radius Figure 10.13 H-R Diagram of Nearby Stars Analogy 10.1 People along a main sequence Main Sequence • • • • Most stars in H-R diagram on main sequence Runs from top left (High luminosity and temp) To bottom right (low luminosity and temp) Runs from blue giants and supergiants to red dwarfs Figure 10.14 H-R Diagram of Brightest Stars More Precisely 10.2 Estimating Stellar Radii Non-Main Sequence • 90% of stars on main sequence • 9% of stars are white dwarfs (bottom left) • 1% of stars are red giants (upper right) Figure 10.15 Hipparcos H-R Diagram Figure 10.16 Stellar Distance Analogy 10.2 Traffic lights further away are fainter Main sequence or not? • Spectral line widths affected by pressure and density • Determines if main sequence or not Table 10-3 Stellar Luminosity Classes Figure 10.17 Stellar Luminosities Table 10.4 Variation in Stellar Properties within a Spectral Class Sun • • • • Spectral class G Subdivision 2 Luminosity class V G2V Binary stars • Most stars are members of multiple-star systems - Binary-star systems (2) most common • Visual binaries (see 2 stars) • Spectroscopic binaries (detect Doppler shift from one or both orbiting stars) • Eclipsing binaries (one passes in front of other, varying light output) Figure 10.18 Binary Stars Determining stellar masses • Measure binary properties • Use orbital radii and period • Universal law of gravitation Figure 10.19 Stellar Masses More Precisely 10.3 Measuring Stellar Masses in Binary Stars Figure 10.20 Stellar Mass Distribution Table 10.5 Measuring the Stars Stellar lifetime • • • • Depends on mass (how much fuel) and Luminosity (how fast fuel is consumed) A B2V star lives 90 million years A G2V star lives 10,000 million years (our sun) • An M5V star lives 16,000,000 million years Table 10.6 Key Properties of Some Well-Known Main-Sequence Stars Figure 10.21 Stellar Radii and Luminosities