The Sun - II

Alexei Gilchrist

Some resources• http://www.nineplanets.org/sol.html• “The Universe: Secrets of the Sun” video

– Search on youtube (references are to clips here http://www.youtube.com/view_play_list?p=4EEF5255D3EEF425parts 1-5)

• Chp 14 of Voyages (references and links at end)• References noted in these slides

Secrets of the Sun

Why does the sun shine?

Long and fascinating history involving - geology - evolution - meteors - E = mc2

- quantum mechanics - particle physics - two Nobel prizes

http://nobelprize.org/nobel_prizes/physics/articles/fusion/index.htmlhttp://www.cerritos.edu/ladkins/a106/sunshine.htmhttp://nobelprize.org/nobel_prizes/physics/articles/bahcall/

More detail:

How much energy does the sun put out?Imagine an ice cube in the sun during summer ... takes about 30min to melt say

That ice cube could be anywhere in a sphere with radius 150,000,000 km around the sun ...

If you put all those ice cubes out there at same time – a shell 1cm thick and surrounding the sun it would all melt in about 30 min

1 calorie (=4.2 J) -> 1g water by 1 degree oC

= 6.3 x1026 W

How much do we produce?recommended daily dietary intake ~ 2000 Calories

(food Calorie = 1000 calories)

NB most of the energy we consume goes in heat

Age of the sun?

http://en.wikipedia.org/wiki/Image:KentGeologyWealdenDomeSimple.svg

In 1859 Charles Darwin estimated it at 300 million years based on the erosion of the Weald in south England

(time enough for evolution to occur)

First edition of The Origin of The Species by Natural Selection

Problem ... no fuel source knownChemical?

The sun would burn out in only 3,000 years

No source known that would supply that much energy

Problem ... no fuel source known

That some form of the meteoric theory is certainly the true and complete explanation of solar heat can scarcely be doubted, when the following reasons are considered: (1) No other natural explanation, except by chemical action, can be conceived. (2) The chemical theory is quite insufficient, because the most energetic chemical action we know, taking place between substances amounting to the whole sun's mass, would only generate about 3,000 years’ heat. (3) There is no difficulty in accounting for 20,000,000 years’ heat by the meteoric theory....What then are we to think of such geological estimates as [Darwin's] 300,000,000 years for the “denudation of the Weald”?

Meteoric impact? Initially favored by Lord Kelvin

http://nobelprize.org/nobel_prizes/physics/articles/fusion/index.htmlbut a huge number should be hitting earth too ...

Problem ... no fuel source knownGravitational Contraction? Helmoltz & Kelvin

Sun shrinking ~ 7inches / day

7000 miles in 10,000 years (recorded history) not noticeable at that time

Estimated age of the sun at 18 million years

(Not enough for evolution)

Darwin removes mention of timescales in later editions of The Origin of The Species by Natural Selection

Fission

1896 Radioactivity discovered (Henri Becquerel)

http://fds.oup.com/www.oup.co.uk/images/oxed/children/yoes/atoms/fission.jpg

Heavy unstable nuclei split apart

release of energyThe discovery of the radio-active elements, which in their disintegration liberate enormous amounts of energy, thus increases the possible limit of the duration of life on this planet, and allows the time claimed by the geologist and biologist for the process of evolution.

Rutherford, 1904

Problem – requires massive unstable elements ... inconsistent with sun’s density and composition

Fusion

1905 Albert Einstein: E = mc2

Difference in weight is released as energy ...a lot of energy

Sun is mostly Hydrogen

Fusion will form Helium

Lots of energy released

weight He < weight 2p +2n

(Aston 1920 looking for isotopes of Neon)

Nucleus2 protons2 neutrons

but like charges repel...protons will repel each other as they both have +ve charge

Is the sun hot enough so that they slam into each and get closeenough for fusion to occur? Eddington 1925:

Sun not collapsing – hydrostatic equilibrium(pressure in = pressure out)

for a gas (pressure) = (density) (temperature)

working from surface downestimated core

of sun at 10 million K

Not hot enough!

Quantum again

Since matter has wave-like behaviour we can get “quantum mechanical tunneling”

Even though the protons don’t have enough energy to fuse they can sort of leak into each other and fuse some of the time

http://hyperphysics.phy-astr.gsu.edu/Hbase/quantum/barr.html#c1

p-p cycle

Hans Bethe received the 1967 Nobel Prize in Physics

"for his contributions to the theory of nuclear reactions, especially his discoveries concerning the energy production in stars"

The p-p cycle

neutrinos

neutrinosHard to detect probability of hitting something in earth

is < 1/1,000,000,000,000

100,000,000,000 pass through your thumbnail every second

could travel through 100 light years of ironwithout hitting anything

Detection:first:o 100,000 gallons of cleaning fluid (perchloroethylene)o Occasional collision with chlorine -> Argono Detect the Argon

o expect only a few atoms / week

e.g. super-Kamiokande: o 50,000 tons of ultra pure watero 11,000 tv-sized detectorso detect flashes of light from a neutrino collision

super-Kamiokandehttp://www.oobject.com/ghost-particle-detectors/super-kamiokande/2172/

“solar neutrino problem”

"for pioneering contributions to astrophysics, in particular for the detection of cosmic neutrinos"

Raymond Davis, Jr. & Masatoshi Koshiba, 2002 Nobel Prize in Phyics

Required a modification of our basic understanding of particle physicso neutrinos have masso can oscillate between other types (electron neutrino, muon neutrino, tau neutrino)o Only electron neutrino detected initially

Sudbury Neutrino Observatory

too few neutrinos detected (factor of three)Energy correct; T of sun verified independently;rate depends on T25 ! x3 is particularly good

Secrets of the Sun(nuclear fusion)(1) 1:14 (5min)

http://www.lmsal.com/YPOP/Spotlight/Tour/tour07.htmlSolar Cycle

o Solar activity goes on an 11 year cycleo last maximum in 2001

http://www.lmsal.com/YPOP/Classroom/Lessons/Cycles/Images/butterfly.gif

http://www.lmsal.com/YPOP/Spotlight/Tour/images/cycle2.jpeg

http://www.nso.edu/gifs/minmax.gif

Secrets of the Sun(solar cycle)

(4) 4:40 (2min)

Magnetic environment

o Can measure this through the Zeeman effect

o Suns activity is driven by magnetism (originating in movement of charged gasses)

Strong magnetic fields split the quantum energy levels and this can be seen in the spectra

Sunspots are regions of strong magnetic fields

Magnetic Environmento coronal loops align with magnetic field lines

http://stargazers.gsfc.nasa.gov/students/magnetism.htm

http://www.space.com/scienceastronomy/solarsystem/trace_update_000926.html

Magnetic Environmento Suns magnetic field is enormously complex – the differential rotation twists the field lines (~ million poles)

Prominences...

o usually originate near sunspots (release of energy from twisted magnetic field lines)o relatively cool: 60,000 Ko loops can remain stable for hours or dayso eruptions faster 1,300 km/s & heights of a million km

Plages...bright clouds: o higher temp and density

Sunspots ...

Solar flareso Violent eruptions (some of the largest explosions in solar system) a billion Mt of TNTo usually 5-10 minutes (largest several hours)o near solar maximum: several smaller flares a day; a large flare every few weekso 10 million K ; lots of UV and X-rayso can cause solar quakeso can emit large amount of coronal material e.g equivalent to mount everest (coronal mass ejections or CMEs)

A solar quake from a flare

- bubble of 10s of millions of tons gas blown into space- can reach earch in a few days- can change the orbits of satellites- distorts earths magnetic field- disrupts communication satellites

Secrets of the Sun(magnetics; coronal loops; sun spots; solar flares;

sun quakes; coronal mass ejections)(2) 2:50 – (3) 1:38 (11min)

Solar windo Discovered by observing comets tails

o stream of charged particleso coronal gases are so hot particles can escape suns gravityo 400km/s outward

o sun losing 10 million tons / year

o bright regions of corona – gases trapped by magnetic fieldso dark regions – magnetic field extends outwardso solar wind predominantly from these “holes”

Effect on Earth - auroraso interaction of solar wind with earths magnetic fieldo complex!

http://science.nasa.gov/spaceweather/aurora/gallery_12oct01.htmlhttp://science.nasa.gov/spaceweather/aurora/gallery_12oct01.html

aurora_img_2005254_sm

Effect on Earth - auroras

http://en.wikipedia.org/wiki/Aurora_(astronomy)

Effect on Earth - auroras

http://en.wikipedia.org/wiki/Aurora_(astronomy)

Effect on Earth - climate

o “little ice age” in europe during maunder minimum (Thames froze at least 11 times)

Why? Solar luminance change too small

Recent model: UV changes 10x – 100x bigger More ozone produced

Absorbs sunlight

Warms stratospherechanges wind patterns

transfer of heat around earth

Effect on Earth – 14C production

http://en.wikipedia.org/wiki/Image:Carbon14_with_activity_labels.svg

http://en.wikipedia.org/wiki/Image:Carbon14-sunspot.svg

more longer term recordsof solar activity

Effect on Earth – solar storms

Secrets of the Sun(CME; solar storms; effect on technology; auroras)

(3) 1:38 – 9:55(4) 0:00 – 4:42 (~13min)