The Sun - II Alexei Gilchrist Some resources - - PowerPoint PPT Presentation

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=4EEF5255D3EEF425 parts 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.html http://www.cerritos.edu/ladkins/a106/sunshine.htm http://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 x102

6 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

• f The Species by Natural

Selection

Problem ... no fuel source known

Chemical?

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.html

but a huge number should be hitting earth too ...

Problem ... no fuel source known

Gravitational 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

• f 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 energy The 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)

Nucleus 2 protons 2 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 close enough for fusion to occur? Eddington 1925: Sun not collapsing – hydrostatic equilibrium (pressure in = pressure out) for a gas (pressure) = (density) (temperature) working from surface down estimated core

• f 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

neutrinos

Hard 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 iron without hitting anything

Detection:

first:

• 100,000 gallons of cleaning

fluid (perchloroethylene)

• Occasional collision with

chlorine -> Argon

• Detect the Argon
• expect only a few atoms / week

e.g. super-Kamiokande:

• 50,000 tons of ultra pure water
• 11,000 tv-sized detectors
• detect flashes of light from a

neutrino collision

super-Kamiokande

http://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 physics

• neutrinos have mass
• can oscillate between other types

(electron neutrino, muon neutrino, tau neutrino)

• 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 T2

5 ! x3 is particularly good

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

http://www.lmsal.com/YPOP/Spotlight/Tour/tour07.html

Solar Cycle

• Solar activity goes on an 11 year cycle
• 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

• Can measure this through the Zeeman effect
• Suns activity is driven by magnetism (originating in movement
• f 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 Environment

• 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 Environment

• Suns magnetic field is enormously complex – the differential

rotation twists the field lines (~ million poles)

Prominences...

• usually originate near sunspots

(release of energy from twisted magnetic field lines)

• relatively cool: 60,000 K
• loops can remain stable for

hours or days

• eruptions faster 1,300 km/s

& heights of a million km

Plages...

bright clouds:

• higher temp and density

Sunspots ...

Solar flares

• Violent eruptions (some of the largest explosions in solar system)

a billion Mt of TNT

• usually 5-10 minutes (largest several hours)
• near solar maximum: several smaller flares a day; a large flare

every few weeks

• 10 million K ; lots of UV and X-rays
• can cause solar quakes
• 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 wind

• Discovered by observing comets tails
• stream of charged particles
• coronal gases are so hot particles can escape suns gravity
• 400km/s outward
• sun losing 10 million tons / year
• bright regions of corona – gases trapped by magnetic fields
• dark regions – magnetic field extends outwards
• solar wind predominantly from these “holes”

Effect on Earth - auroras

• interaction of solar wind with earths magnetic field
• complex!

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

• “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 stratosphere changes wind patterns transfer of heat around earth

Effect on Earth – 1

4C production

http://en.wikipedia.org/wiki/Image:Carbon14_with_activity_labels.svg http://en.wikipedia.org/wiki/Image:Carbon14-sunspot.svg

more longer term records

• f 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)