Unformatted text preview:

1Class 25The Structure of the Sun Basic structure of the Sun Hydrostatic equilibrium Surface phenomena2I : The structure of the Sun Core (R<0.25Rsun) Extremely hot (1.5x107 K at center) Extremely dense (1.6x105 kg/m3) Site of energy generation (thermonuclear fusion) More next class… Radiative zone (0.25Rsun→0.7Rsun) Energy transported outwards by radiative diffusion Essentially, photons “random walk” their way outwards Takes about 170,000 years for energy to leak out! Convective zone (0.7Rsun→Rsun) Temperature low enough (below 2x106K) that somecombined hydrogen nuclei form. Gas become much more effective at absorbing radiation…chokes radiative diffusion process Energy transport continues via convection Photosphere, chromosphere and corona More later…34II : Hydrostatic equilibrium What supports the Sun against collapsing in itsown gravitational field? Consider any slab of gas in the Sun… it is inequilibrium (i.e., zero net force) when This is the equation of hydrostatic equilibrium Quick note (beyond ASTR120 level)… the actualequation for a spherical object like the Sun isDifference in pressureforces on top andbottom of slabWeight ofgas in slab= -5III : Surface phenomena Outer regions of the Sun (above convectivezone) consists of three layers Bottom layer : Photosphere Visible surface of Sun Top of the convective zone; T=5800K Can see convective cells Next : Chromosphere Region of hotter gas Temperature increases with height Displays spicules Finally : the Corona Very hot gas (million K or more); emits X-rays Most likely heated by phenomena associated withmagnetic fields6789 Many important phenomena are driven bymagnetic fields… Sunspots Regions where magnetic fields pierce the photosphere Prominences, flares and coronal mass ejections… Explosive events associated with the unraveling of astressed, twisted magnetic field Can send bursts of high-energy particles into space…can be problem for satellites and astronauts Magnetic phenomena have an 11 year cycleassociated with the solar


View Full Document
Download Class 25 The Structure of the Sun
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view Class 25 The Structure of the Sun and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Class 25 The Structure of the Sun 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?