Download The Quivering Sun: Helioseismology (PowerPoint version)

The ‘Quivering Sun’
Helioseismology
The Physics of Music
Why do various musical instruments
sound so very different, even when they
play exactly the same note?
What makes a Stradivarius great?
Why do the top notes on a piano
sound ‘tinny’ and musically uninteresting,
unlike the rich notes in the middle?
Standing Waves
Visit the following website:
http://zonalandeducation.com/mstm/physics/waves/standingWaves/standingWaves1/StandingWaves1.html
to see how‘harmonics’ (or ‘overtones’) accompany the
fundamental vibration of a violin string.
Watch the complex vibrations of a real guitar string:
https://www.youtube.com/watch?v=ttgLyWFINJI
More Than Just the Single Strings!
Other factors enter:
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One vibrating string can set another one vibrating
‘sympathetically’ – it resonates. This is one reason that
electronic pianos do not sound the same as ‘acoustic’
pianos (but the effects can be simulated).
The whole body of the instrument also vibrates,
contributing to the richness of the sound.
Chladni
He studied vibrations and nodes (places where there is no
motion) on 2-dimensional surfaces, like the round or square
head of a drum. In general, all these vibrational modes
participate at once (to a greater or lesser degree)
http://www.acs.psu.edu/drussell/Demos/MembraneCircle/Circle.html
http://www.acs.psu.edu/drussell/Demos/MembraneSquare/Square.html
This Applies From Small to Large
These vibrational modes exist everywhere, all the way from small
molecules like water (H2O) and benzene (C6H6)
https://www.youtube.com/watch?v=1uE2lvVkKW0
(water)
https://www.youtube.com/watch?v=NA9etutSt7A
(benzene)
up to the scale of the sun and stars (next slide).
GONG
The Global Oscillations Network Group
http://gong.nso.edu
Modes of vibration in the Sun!
Helioseismology
There are numerous modes, of varying scales and
amplitudes.
As in musical instruments (and molecules!), many modes of vibration
may be happening at once. The sun ‘rings like a bell.’
To measure this activity, we take spectra of the light at umpteen points
on the surface of the Sun (not just looking at the tops of individual
convective cells, but also averaged over larger patches) and study
the Doppler shifts to look for coherent up-and-down (in-and-out)
motions.
One Special Vantage Point
Here, we can monitor the sun continuously for months!
But Why Does the Sun ‘Jiggle’?
On Earth, seismology depends
on the fact that occasional
earthquakes send shock waves
through the solid body. These
earthquakes are caused by
energy flowing out from the
hot core. The Earth does not
need to be ‘tolled’ (struck) like a bell.
Similarly for the sun: it does not need to be struck by infalling
comets or asteroids (although that does happen from time to
time). The complex churning motions within the sun explain the
ongoing seismic activity.
What Have We Learned?
Helioseismology allows us to investigate the physical structure of
the sun -- the temperature and density, etc -- right down into
its innermost parts. (It is a complex analysis!)
These can be interpreted to indicate how much hydrogen has so
far been converted to helium in the centre, allowing us to test
the correctness of the so-called SSM (Standard Solar Model);
we can also deduce its age.
The conclusions completely reinforce what we already knew!
The Sun is about 4.6 billion years old, and is converting H to
He in the way we described earlier – just as the neutrinos
said.
We are ready to address the stars!