How Do We Know?

The Electromagnetic Spectrum
can be described in terms of a stream of photons, each traveling in a wave-like pattern, moving at the speed of light
and carrying some amount of energy. It was pointed out that the only difference between radio waves, visible light,
and gamma-rays is the energy of the photons. Radio waves have photons with low energies, microwaves have a little more
energy than radio waves, infrared has still more, then visible, ultraviolet, X-rays, and gamma-rays.

EMS

Here's a really good NASA explanation of the Electromagnetic Spectrum

NASA EMS Page

some things to note

Radiation is Energy emitted in the form of waves (light) or particles (photons).
In many cases, people may say a photon "sometimes acts like a wave, and sometimes acts like a particle". This is slightly misleading, because a photon always acts like both.

Cosmic Rays
(Are not part of the Electromagnetic Spectrum)
In astrophysics, cosmic rays are radiation consisting of energetic particles originating beyond the Earth that impinge on the Earth's atmosphere. Cosmic rays are composed mainly of bare nuclei, roughly 87% protons, 12% alpha particles (helium nuclei) and most of the rest being made up of heavier atomic nuclei. Electrons, gamma rays, and very high-energy neutrinos also make up a much smaller fraction of the cosmic radiation. They originate in energetic events from beyond the solar system and travel very close to the speed of light.

Solar Spectrum

Stellar Spectra

The Classification of Stars

The HR Diagram.

HR Axis

The Horizontal Axis = Spectral Type, or Temperature

Each spectral class is subdivided into 10 parts

O_{0 ,}O_{1 ,}O_{3 ...}O₉B_{0 ,}B_{1 ,}B_3
...B9

etc.

Our Sun is Spectral Type G₂,
Surface Temperature 5,500 ˚ K (11,000 ˚ F)
Color = Yellow

The spectral classes have been expanded to to include

W, O, B A, F. G, K, M, R, N, S

The Vertical Axis = Absolute Magnitude or Luminosity

The Sun's Luminosity is = 1

Luminosity is the total brightness of a star (or galaxy). Luminosity is the total amount of energy that a star radiates each second relative to the sun.

The Sun's aboslute magnitude = +4.56

Absolute magnitude is a measure of the inherent brightness of a celestial object. This scale is defined as the apparent magnitude a star would have if it were seen from a standard distance of 32.6 light-years (10 parsecs). The lower the number, the brighter the object. Negative numbers indicate extreme brightness.

Parallax is the apparent change in the position of a star that is caused only by the motion of the Earth as it orbits the Sun. Friedrich Wilhelm Bessel first detected the parallax "motion" of a star in 1838 observing the star 61 Cygni (this was definitive proof that the Earth orbits the Sun, and not the other way around).

PARSEC
A parsec is a unit of distance that is equal to 3.26 light-years. It is the distance at which a star would have a parallax of 1 second of arc

.

Yerkes Classification of stars( Includes Luminosity)

Ia    Most luminous Supergiants
Ib    Less luminous Supergiants
II    Luminous Giants
III    Normal giants (Red Giants)
IV    Subgiants
V   Main sequence stars (Dwarfs)

HR-Yerkes

The sun is a G₂V Yellow Dwarf

60% of the visible stars are binary or multiple star systems.

These pictures will link you to the Space Telescope Institute and detailed information about the pictures

End Points

	White Dwarfs	Neutron Stars	Black Holes
Radius	1000 - 10000 Km	10 - 100 Km	0
Density	10⁶ to 10⁸ gm/cm3	10¹⁴	infinite
Initial mass	M < 5 solar masses	M > 8 Solar Masses	?
M (remnant)	M < 1.4 SolarM M > 0.7 SolarM White Dwarf	M < 3.2 SolarM	M > 3.2 Solar M

Examples of End Points
Dwarf Stars become Planetary Nebulae

An Animation showing changes over time as the star's palnetary shell expands
4368.gif

Helix Nebula

Ghost Nebula

More Links about the Evolution of the Sun

http://astrosun.tn.cornell.edu/courses/astro201/evol_sun.htm

http://www.deltastate.edu/academics/artsci/physci/astronomy/NatureStars/img0.htm

http://javalab.uoregon.edu/dcaley/elements/Elements.html

http://www.solarviews.com/eng/sun.htm
http://www.enchantedlearning.com/subjects/astronomy/sun/sunstructure.shtml

http://science.nasa.gov/newhome/pad/sun_today.htm
http://www.genesismission.org/science/mod3_SunlightSolarHeat/SolarStructure/

Sample Super Nova
M-1 The Crab Nebula

A Neutron Star

SN1987A_Rings

More Links with more details about Stellar Evolution

http://zebu.uoregon.edu/~soper/Stars/hrdiagram.html
http://csep10.phys.utk.edu/astr162/lect/light/absorption.html

http://www.ukaff.ac.uk/movies.shtml
http://leo.astronomy.cz/sclock/sclock.html
http://instruct1.cit.cornell.edu/courses/astro101/java/evolve/evolve.htm
http://zebu.uoregon.edu/textbook/se.html
http://plabpc.csustan.edu/astro/stars/Stars.htm

Simulations

Special Cases

movies were produced on the UKAFF computer.
http://www.ukaff.ac.uk/movies.shtml

Next

Cosmology

http://terpsichore.stsci.edu/~summers/viz/scviz/barnes_group.html
http://www.mpa-garching.mpg.de/Galaxien/movies.html
http://ourworld.compuserve.com/homepages/anima/rfslink.htm
http://school.discovery.com/schooladventures/universe/itsawesome/cosmiccalendar/page2.html
http://www.electric-cosmos.org/darkmatter.htm

How Do We Know?

Birth of a star Called Sun