* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download The Stars - University of Redlands
Space Interferometry Mission wikipedia , lookup
Spitzer Space Telescope wikipedia , lookup
Constellation wikipedia , lookup
Astrophotography wikipedia , lookup
Aries (constellation) wikipedia , lookup
Canis Minor wikipedia , lookup
Corona Borealis wikipedia , lookup
Dialogue Concerning the Two Chief World Systems wikipedia , lookup
Corona Australis wikipedia , lookup
Auriga (constellation) wikipedia , lookup
Astronomical unit wikipedia , lookup
Cassiopeia (constellation) wikipedia , lookup
Perseus (constellation) wikipedia , lookup
Cygnus (constellation) wikipedia , lookup
Canis Major wikipedia , lookup
International Ultraviolet Explorer wikipedia , lookup
Future of an expanding universe wikipedia , lookup
H II region wikipedia , lookup
Star catalogue wikipedia , lookup
Stellar classification wikipedia , lookup
Timeline of astronomy wikipedia , lookup
Aquarius (constellation) wikipedia , lookup
Stellar evolution wikipedia , lookup
Observational astronomy wikipedia , lookup
Corvus (constellation) wikipedia , lookup
Stellar kinematics wikipedia , lookup
Stars … how I wonder what you are. 7 Goals Tie together some topics from earlier in the semester to learn about stars: • How do we know how far away stars are? • How do we know how bright they really are? • What are they like? – Temperature – Radius – Mass • What categories can we place them in? 7 Distances • • • • How do we perceive distances here on Earth? How do we know A is closer than B? Can we apply these to objects in space? Can we apply these to objects beyond the solar system? • How do we know how far away the stars are? 7 Stellar Parallax • One proof of a heliocentric Universe is stellar parallax. – Tycho Brahe saw no parallax of stars. – Copernicus thought stars must be too far away. • Nearest star: Proxima Centauri Parallax angle = 0.76 arcsec – Tycho’s precision = 1 arcmin 7 The Parsec • Triangles: tan q = opposite/adjacent • For small angles: tan q = q q = (1 AU)/Distance Distance = (1 AU)/q • What is the distance of an object with q = 1 arcsec? Distance = 206,265 AU • Call this distance 1 parsec (pc) • 1 pc = 206,265 AU = 3.3 lightyears 7 Distances 1 Distance (in parsecs) parallax (in arcsec) • • • • 1 parsec = distance with a parallax of 1 arcsecond. 1 lightyear = distance light travels in one year. 1 pc = 206,265 AU = 3.3 lightyears Closest star: Proxima Centauri q = 0.76 arcsec Distance = 1.3 pc or 4.3 lightyears 7 How far is this? The Sun Hawaii Alpha Centauri New York 7 Star light, star bright • In lecture 5 we talked about stellar magnitudes. • Sirius is magnitude –1.5 Polaris is magnitude 2.5 • While Sirius is brighter than Polaris, Sirius is also a lot closer to us. 7 Apparent and Absolute • Apparent Magnitude = the brightness (magnitude) of a star as seen from the Earth. m – Depends on star’s total energy radiated (Luminosity) and its distance • Absolute Magnitude = the brightness (magnitude) of a star at a distance of 10 pc. M – Only depends on a star’s luminosity distance m M 5log 10 10pc 7 example distance m M 5log 10 10pc • Our Sun: – m = -26.8, – distance = 1/206,265 = 4.8 x 10-6 pc So: M = 4.8 • Polaris: – m = 2.5, – distance = 132 pc So: M = -3.1 • Polaris is 1500 times more luminous than the Sun! 7 Stellar Temperatures Stellar Spectra How hot are stars? • In Lecture 3 we learned about blackbody spectra and temperature. • Since different stars have different colors, different stars must be different temperatures. Hot Cool 7 Spectral Classifications 7 Orion Copyright – Tyler Nordgren 7 Stellar Masses How massive are stars? • Kepler’s Laws – devised for the planets. • Apply to any object that orbits another object. • Kepler’s Third Law relates: – Period: “how long it takes to orbit something” – Semimajor axis: “how far you are away from that something” – Mass: “how much gravity is pulling you around in orbit” 3 a P M 2 • Where M is the Total Mass. • Can calculate the mass of stars this way. 7 Binary Stars • Most stars in the sky are in multiple systems. • Binaries, triplets, quadruplets, etc…. – Sirius – Alcor and Mizar • The Sun is in the minority by being single. 7 Spectroscopic Binaries • Sometimes you can’t see both stars. – Too close – Too far – Too faint • But if a star is orbiting something it must be moving. 7 NPOI Observations of Mizar A (1 Ursa Majoris) 0.01 arcsec Orbital Phase: 000o Mizar, 88 light years distant, is the middle star in the handle of the Big Dipper. It was the first binary star system to be imaged with a telescope. Spectroscopic observations show periodic Doppler shifts in the spectra of Mizar A and B, indicating that they are each binary stars. But they were too close to be directly imaged - until 2 May 1996, when the NPOI produced the first image of Mizar A. That image was the highest angular resolution image ever made in optical astronomy. Since then, the NPOI has observed Mizar A in 23 different positions over half the binary orbit. These images have been combined here to make a movie of the orbit. As a reference point, one component has been fixed at the map center; in reality, the two stars are of comparable size and revolve about a common central position. 7 Stellar Masses How massive are stars? 3 a P M 2 • Where M is the Total Mass of the binary. • Most stars have masses calculated this way. • Result: – The more massive the star, the more luminous it is. – The more massive the star, the hotter it is. 7 Stellar Radii How big are stars? • We see stars have different luminosities and different temperatures. • Stars have different sizes. • If you know: 50 mas – Distance – Angular size • Learn real size. 7 Stars are small • Betelgeuse is the only star big enough to directly see its surface with a normal telescope. 7 Interferometry • Combine the light from two or more telescopes to simulate the RESOLUTION of one giant telescope. NPOI - optical VLA - radio 7 Optical Interferometry • NPOI simulates a single optical telescope 65 meters in diameter. • Resolve stars as small as 1.5 mas! PTI - infrared 7 Angular versus Linear Supergiants, Giants and Dwarfs 7 H-R Diagram • Can order the stars we see by the property of temperature and luminosity (or absolute magnitude). Prominent stars Nearby Stars Brightest Stars 1000 pc Stars 7