The Sun
Physical Data Mass = 2x10 30 kg (333,000 time more massive than the Earth) Diameter: 7x10 5 km (about 100 Earth radii) Volume: you can fit about 1.3 million earths inside the sun! 70% Hydrogen, 28% Helium, 2% other stuff.
Distance to the sun The average earth-sun distance is called an Astronomical Unit (AU) 92.8 Million Miles Keppler knew the distance to the planets in terms of the Earth- Sun distance, but not the distance itself (in meters)
Interior of the Sun VERY hot (27 million F) and dense (150 times denser than water) in the center (core) Density drops rapidly toward the outside 10,000 F at the surface
Core of the sun The temperatures, gravity, and densities are super high! How high? High enough to push hyrdogen protons together. They fuse to form helium. What is this called?
Fusion in the sun
Core of the sun 4 protons have more mass than one Helium. The lost mass is turned into massive amounts of energy (E=mc 2 ) Thanks Einstein. Again, nuclear fusion occurs in the core of the sun.
Fusion in the sun
Photosphere Photosphere brightest in optical this is where most of the light from the sun comes from. The spectrum is formed here.
Photosphere Optical light comes from here Sunspots are areas of intense magnetic field
The Sun s Future? The sun is currently crushing hydrogen into helium in the process of nuclear fusion. The sun is currently 70% hydrogen and 28% helium. How will these numbers change as time goes on?
The End
Chromosphere Activity starts at sunspots and gas travels along magnetic field lines If the gas loops back
Coron a The top picture is in X- ray The bottom two are in optical from SOHO You can see material leaving the sun
Energy transfer The energy created in the center of the sun has to travel to the outside. This happens in an orderly fashion in the interior Near the outside, energy is transferred with convection
Measurements What we can measure Distance to Venus (radar) Apparent mag. of sun (and D) Period of the Earth s orbit (and D) Spectrum of the sun Sunspots What we can calculate Distance to the sun Absolute mag. (Luminosity) Mass of Sun Temperature, chemical composition, rotation Rotation Rotation, magnetic field
The sun as a main sequence star The sun is a G2 main sequence star with an absolute magnitude of 4.85 All main sequence stars change H to He All spectra come from the photospheres of the stars We can only detect the chromosphere and corona of a few stars besides the sun
Properties of Stars
Properties of Stars Brightness Luminosity (brightness and distance) Magnitude scale Temperature (Color, spectrum) Composition (Spectrum) Velocity, rotation, magnetic field (spectrum) Distance (parallax, comparison)
Triangulating the Stars Image from Nick Strobel s Astronomy Notes (http://www.astronomynotes.com)
Brightness and Luminosity Apparent magnitude measures the brightness of a star The true property of the star is luminosity. Luminosity, the total power coming from the surface of a star, is measured using Absolute Magnitude
Calculating Magnitude s You need to know the distance to the star in question (parallax for the nearest stars harder for everything else) Then you can calculate the absolute magnitude, M
Putting it together: an HR diagram Luminosity is measured in Watts or absolute magnitude Brightness is measured in Watts/m 2 or apparent magnitude Temperature is measured in color or spectral type (OBAFGKM)
Types of HR diagrams Theorist s Observer s Color-magnitude
Absolute Magnitude Absolute Magnitude vs. Spectral Type Here is an HR diagram for a few hundred randomly selected stars from the HD catalog -7.00-5.00-3.00-1.00 1.00 3.00 Notice the main sequence 5.00 7.00 9.00 11.00 0 1 2 3 4 5 6 7 Spectral type
Luminosity Classes of Stars Again, on the basis of the appearance of the spectra of stars, astronomers discovered that the density of gas and the strength of gravity at the surface of a star indicate that some stars are much larger than other, even if their temperatures are the same. This difference is denoted by the luminosity class of a star. The sequence of luminosity classes is: Luminosity Class Name assigned to class: I or Ia Supergiants II Bright Giants III Giants IV Sub-giants V Dwarfs VI Sub-dwarfs The complete classification of a star is based upon the spectral type and luminosity class of a star. Thus, it turns out that the sun is classified as a G2V star. Our old friend Betelgeuse is an M1I star.