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The Sun and The Basic Properties of Stars


Atmosphere and Interior of the Sun. The sun's atmosphere. Corona. Chromosphere. Photosphere. The sun's interior. Convection zone. Radiation zone. Core ... – PowerPoint PPT presentation

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Title: The Sun and The Basic Properties of Stars

The SunandThe Basic Properties of Stars
The Sun
  • Basic Properties
  • Mass- 2 x 1030 kg
  • Radius- 6.96 x 105 km
  • Luminosity- 3.8 x 1026 J/sec
  • Essentially a giant ball of plasma
  • Mainly composed of hydrogen and helium
  • 70 hydrogen
  • 28 helium
  • 2 heavier elements

Atmosphere and Interior of the Sun
  • The suns atmosphere
  • Corona
  • Chromosphere
  • Photosphere
  • The suns interior
  • Convection zone
  • Radiation zone
  • Core

Image SolarScapes, Space Science Institute
Nuclear Fusion
  • Nuclear fusion takes place in the suns core
  • Hydrogen ? Helium by a process known as the
  • Proton-Proton Chain
  • Four hydrogen protons fuse to eventually make
  • Loss of mass during process energy

Proton-Proton Chain
  • The proton-proton chain is basically a three-step
  • 1. Two hydrogen protons fuse to make a deuterium
    nucleus with one proton and one neutron (occurs
  • 2. The deuterium nucleus fuses with another
    hydrogen proton, creating helium-3 (occurs twice)
  • 3. The two helium-3 nuclei fuse and form
    helium-4, releasing two extra protons

Proton-Proton Chain
  • The end of the chain
  • The extra protons stay in the Sun's core for
  • subsequent nuclear reactions
  • The gamma rays are reradiated as lower energy
  • This process of nuclear fusion requires high
    density and high temperatures
  • The core must remain hot and dense to allow this
  • These conditions are maintained by gravitational

Gravitational Equilibrium
  • Pressure from the weight of the overlying layers
    causes increased pressure in the core

The Basic Properties of Stars
The Distance of Stars
  • Stellar parallax is the shift in a stars
    apparent position caused by the Earths orbit of
    the sun
  • Most direct method of measuring the distance of a
  • The apparent location of a star is observed at
    the beginning and end of a six month period

Stellar Parallax
  • Here, d is the distance of the star measured in
    parsecs, and p is the parallax angle
  • Distance of the star
  • d1/p

Proper Motion
  • The number of arc seconds per year (or century)
    that a star moves across a background of stars
    and/or galaxies is the stars proper motion.

Star Magnitudes
  • Absolute magnitude (MV)- a measure of a stars
    luminosity (the apparent magnitude if the star
    were 10 parsecs away)
  • MV m V 5 5 log d
  • Here, MV is the absolute magnitude, while m V is
    the apparent magnitude and d is the distance of
    the star

Hertzsprung-Russell Diagram
  • Using the aforementioned absolute magnitudes of
    stars and plotting them against the spectral
    types of each, Hertzsprung and Russell created a
    diagram that catalogued this data from many
    stars, and they found a pattern.
  • By using MV v. spectral types, Hertzsprung and
    Russell found that many stars fell on a diagonal
    line that ran from the top left to the bottom
    right a line known as the main sequence.

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Binary Star Systems
  • A binary star system is two stars that orbit one
    another. There are three types of these systems.
  • Visual binary- a pair of stars whose orbit can be
  • Eclipsing binary- a pair of stars that orbit in
    our line of sight, thus the eclipse of the stars
    can be observed
  • Spectroscopic binary- a system whose orbit is
    revealed by observing Doppler shifts in its
    spectral lines
  • By using Keplers Third Law, the mass of the
    stars can be derived.
  • P2 4 p2a3 / G(MA MB)
  • With the mass known, the main-sequence lifetime
    of the star can be found.

Main-Sequence Stars
  • Stars on the main sequence have a certain
    lifetime during which they remain a main-sequence
    star and continue converting hydrogen to helium
  • This lifetime, in respect to that of our sun, can
    be found by comparing the stars mass against
    that of our sun
  • TStar/TSun (MStar/MSun) -2.5
  • Here, T is the luminosity and M is the mass of
    the star