The Sun, a Star Astronomy 360 Notes (Physics 360/Geol 360) Dr. Swez Note: Slide which are important...
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Transcript of The Sun, a Star Astronomy 360 Notes (Physics 360/Geol 360) Dr. Swez Note: Slide which are important...
The Sun, a Star
Astronomy 360 Notes (Physics 360/Geol 360) Dr.
Swez
Note: Slide which are important and should be reviewed are marked as
What Is the Sun?
A big, hot ball of gas
The Sun and planets are shown to the same scale. The small terrestrial planets and tiny Pluto are in the box---the Earth is the blue dot near the center of the box.
1. From Nick Strobel's Astronomy Notes. Go to his site at www.astronomynotes.com for the updated and corrected version. Created by Nick Strobel using NASA images
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Physical Data on the Sun Mass 2x1030 kg
Watch planet orbits
Radius 110 REarth Use distance and trig
Luminosity 4x1026 W Use distance and value at Earth Also Stephan-Boltzmann Law
Surface Temp 5800K
Wien’s Law
Eq Rotation 25 days
Polar Rotation 33 days
Watch Sunspots
Composition: 71% H, 27% He, 2% Other
Examine spectrum
From: Explorations by Thomas Arny, page 325
The Mass Luminosity Law for stars
Where is the sun on this graph?
Remember the Stephan-Boltzmann Law?
Look ahead to p 363-365 text
A body of temperature T radiates an amount of energy each second equal to T4 per square meter. If we know the energy per square meter we can find the temperature.
= 5.67 x 10-8 watts m-2 K-4
From Nick Strobel's Astronomy Notes. Go to his site at www.astronomynotes.com for the updated and corrected version.
The Photosphere (surface of the sun we see) is about 500 kilometers thick.
Note: Image Not in your Text!
Remember Wien’s Law (page 103 text)
Measure the body’s brightness at different wavelengths to find at which particular wavelength it is brightest.
Use Wien’s law to calculate the body’s temperature.
T = (3 x 106 / m)
Where Does the Energy Come From? Coal - lasts a few thousand years Gravothermal Energy
Gravity compresses Sun, which heats it
Could last 20 million years Nuclear Fusion
Energy is converted to mass (E=mc2) Could last 10 billion years
Mass-Energy Conversion Energy = mass x (speed of light)2
(1kg) x (3x108m/s)2 = 1017 joules watt = 1 joule/second
Annual US Energy Consumption ~1020 J The Sun fuses hydrogen into helium
The mass input is greater than the mass output
Some mass is converted to energy
Proton-Proton Chain Hydrogen fuses into helium Summary: 6 H -> 2H + 1 He + +
3x10-7 J Requires very hot temperatures and
high pressures (above 1 million K) The solar core will burn for a total of 10
billion years (How long do we have left?)
Know the full chain!
Neutrinos Neutrinos are small, neutral particles
They easily pass through matter Several light-years of lead can block them
Therefore they are very hard to detect Neutrinos can cause nuclear change in
atomic nuclei Underground detectors see a few each
day
Solar Neutrinos Solar neutrinos are the only direct probe of the
Solar core Detectors reported ~1/3 of the expected
neutrinos New results -> new physics Apparently, neutrinos oscillate between states So, the Sun produces the correct number of
neutrinos for current models There is no longer a ‘Solar Neutrino problem’
What if Hydrostatic Equilibrium Failed? What if gravity exceeded gas
pressure? The Sun would start to collapse The core temperature and pressure would
increase The nuclear fusion rate would increase Hydrostatic equilibrium would be restored!
What if gas pressure exceeded gravity?
Solar Atmosphere Photosphere
surface we see 5800 K contains sunspots
and granulation Chromosphere
cooler outer layer 4500 K contains spicules
Corona very thin outer
layer few million K visible during
eclipse contains flares and
prominances
Why are sunspots dark?
From The WEBSITE: http://www.kis.uni-freiburg.de/~pnb/granmovtext1.html
Granulation in the photosphere of our SUN. A time lapse movie.
A 27 x 27 Mm2 FieldCondensed into 35 minutes
“The series was observed with a fast frame selection system on June 5, 1993, at the SVST (La Palma) in cooperation with G. Scharmer (Stockholm) and G. W. Simon (Sunspot); N. Hoekzema (Utrecht), W. Mühlmann (Graz), and R. Shine (Palo Alto) were involved in the data analysis. Technical data: wavelength 468 ± 5 nm; exposure time 0.014 s; rms contrast (uncorrected) between 7 and 10.6 %. The images were registered, destretched, corrected for the telescope's point spread function, and subsonically filtered after interpolation to equal time steps. “
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Time lapse movies of solar granulation evolution.
The movies show time lapse series of the evolution of the solar granulation, which represents the top of the Sun's convection zone. At the centers of granules hot solar gas rises and radiates its heat rapidly into space; the gas then is diverted horizontally, and sinks back into the Sun in the darker intergranular lanes. The sizes of the granules range from approx. 250 km (the limit set by the telescope and the Earth's atmosphere) to more than 2000 km, with an average diameter of 1300 km. Lifetimes of granules typically range from 8 to 15 minutes. Horizontal and vertical velocities of the gas motion are 1 to 2 km/s.
Courtesy of: http://www.kis.uni-freiburg.de/~pnb/granmovtext1.html
H Alpha Sunspot Images taken at Holloman Air Force Base over a 10 day period.
From: http://www.sunspotcycle.com/Sunspots are cooler dimmer regions with strong magnetic fields.
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Can last months
Erupts over days
Complete Sunspot Data from http://www.sunspotcycle.com/
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How can astronomers detect magnetic fields in astronomical bodies
One way would be to place a magnetometer on the sun. (Impossible!).
A better way is to use the Zeeman effect; a physical process by which the magnetic field splits some of the spectral lines of a gas into more than one component. The magnetic field alters the atom’s electron orbits which in turn alter the emitted wavelength. (see page 345 text)
Sun Spot Data for a Period of about 10 Years
Solar Cycle #23 is in progress. The next sunspot maximum is predicted to occur in the year 2000.
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