solar science workshop 6/8/05 an introduction to the physics of our star: the sun distance from...
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Solar Science Workshop6/8/05
An Introduction to the Physics of Our Star: The Sun
• Distance from Earth– 1 AU
• Travel time for Light to Earth– About 8 minutes
• Travel time for solar wind to 1 AU– A few days
• Mean surface temperature– 5800K
• Temperature in the Center– 1.55x107 K
Solar Science Workshop6/8/05
The Sun
• Mass– 333,000 Earth Masses– More mass than all of the
other objects in the solar system combined
• Diameter– 218 Earth Diameters
• Average Density– 1410 kg/m3
• Composition (by mass)– 74% Hydrogen, 25%
Helium, 1% other elements
Sun seen in Xrays
Solar Science Workshop6/8/05
The Sun Seen From Earth by Amateurs
• COMMON SENSE WARNING …
NEVER LOOK DIRECTLY AT THE SUN WITHOUT A PROPER FILTER !!– Looking directly at the Sun
without the proper filter WILL cause permanent eye damage
• Safest to use the method of projection– Project the image onto a
piece of paper– Can see sunspots, and
even “graph” them easily
Solar Science Workshop6/8/05
The Sun Seen From Earth by Amateurs
• Using a Baader solar filter– Inexpensive– Many “solar
observing glasses” are made out of this material
– Used to see sunspots
– Similar to Mylar
Solar Science Workshop6/8/05
The Sun Seen From Earth by Amateurs
• Hα filters– Much more pricey
• 100s-1000s of dollars
– Can see features in the solar chromosphere
– Used to see Prominences, filaments, flares
– Very impressive Sun seen with an Hα filter
Solar Science Workshop6/8/05
How Old is the Sun ?
• Probably about the same age as Earth
• Has it been shining brightly the entire time?– The luminosity has
probably increased with time, but it has always been very bright
• What is the “fuel” that keeps it shining this long?
Solar Science Workshop6/8/05
The Sun’s Energy Source is ThermonuclearFusion in its Core
• Proton-proton chain– Four hydrogen nuclei “fuse”
to form a single helium nucleus
– There is a slight loss of mass in this process which is converted to energy according to Einstein’s famous equation E = mc2
• Thermonuclear fusion occurs only at the very high temperatures at the Sun’s core
• Fusion should not be confused with fission !
• Will continue to heat the Sun for another 5 billion years
Solar Science Workshop6/8/05
The Proton-Proton Chain
Solar Science Workshop6/8/05
The Structure of the Sun
• The Interior– Core– Radiative zone– Convection zone
• The Surface and Atmosphere– Photosphere– Chromosphere– corona
Solar Science Workshop6/8/05
The Sun’s Interior• Hydrogen fusion takes place
in a core extending from the Sun’s center to about 0.25 solar radius
• The radiative zone extends to about 0.71 solar radius– Here energy travels
outward through radiative diffusion
• The convective zone is a rather opaque gas– Here energy travels
outward primarily through convection
Solar Science Workshop6/8/05
Where do the Neutrino’s and γ-ray photons go ?
• Neutrino’s exit the Sun, unimpeded– Can be used to probe the
solar interior– Early attempts at detecting
them found that their were about 3 times less seen at Earth than there should be
– THE SOLAR NEUTRINO PROBLEM !
• The gamma rays collide with matter and take millions of years to exit the Sun
Solar Science Workshop6/8/05
Detecting Solar Neutrinos
• Underground detectors are used to avoid interference from cosmic rays
Solar Science Workshop6/8/05
The Solution to the Solar Neutrino Problem
• Particle Physics gave us the answer– Solar neutrinos oscillate and the original
detectors could only see certain parts of the oscillations and not all of them
– New detectors were built to observe all neutrinos
– Two physicists won a Nobel Prize for their work
• Modern detectors are placed at different depths within the Earth to observe the actual oscillations
Raymond Davis Jr.
Masatoshi Koshiba
Solar Science Workshop6/8/05
Solar Structure
• The standard solar model
– Theoretical model used to determine the physical properties of the Sun’s interior
– Assumes hydrostatic and thermal equilibrium
Solar Science Workshop6/8/05
Solar Oscillations
• Waves can propagate through the Sun causing a variety of vibrations– Like sound waves
• These are used to infer pressures, densities, chemical compositions, and rotation rates within the Sun
Solar Science Workshop6/8/05
Helioseismology
• The branch of science that studies solar oscillations is known as Helioseismology
• The movie shows evidence of seismic activity on the Sun as seen by the SOHO MDI experiment
Solar Science Workshop6/8/05
The Convection Zone
• The convection zone is just outside the radiative zone. – Thickness is about 200,000 km
• Turbulent convective motions occur, similar to a pot of boiling water.
• Overturning (bubbling) motions inside the Sun are responsible for the granulation pattern seen on the Sun’s surface.
Solar Science Workshop6/8/05
Convection Cells
Solar Science Workshop6/8/05
• Convection cells that are about 1000 km wide
• These are part of the Sun’s atmosphere known as the Photosphere
Solar Granulation
Solar Science Workshop6/8/05
Recent High-resolution Images of
granulation
Solar Science Workshop6/8/05
“Flowers” and
Ribbons
• Produced by magnetic fields
Solar Science Workshop6/8/05
The photosphere is the lowest of three main layers
in the Sun’s atmosphere
• The Sun’s atmosphere has three main layers: the photosphere, the chromosphere, and the corona
• Everything below the solar atmosphere is called the solar interior
• The visible surface of the Sun, the photosphere, is the lowest layer in the solar atmosphere
• The photosphere undergoes “differential” rotation
Solar Science Workshop6/8/05
Limb Darkening
• The edges of the Sun appear darker than that seen “straight on”
• This is called limb darkening
• It is due to the fact that the temperature in the photosphere decreases with altitude
Solar Science Workshop6/8/05
The Origin of Limb Darkening
• The light we see at the limb originated higher up in the atmosphere where it is cooler
– Thus it will be less bright there
Solar Science Workshop6/8/05
Sunspots• Low temperature
regions– How do we know
this ?
• Darkest part is called the “umbra”
• Just outside the umbra is the penumbra
• Associated with Intense magnetic fields
Solar Science Workshop6/8/05
Solar Science Workshop6/8/05
Sunspots Often Come in Groups
Solar Science Workshop6/8/05
The Chromosphere
• Above the photosphere is a layer of less dense but higher temperature gases called the chromosphere
“Color Sphere”
• characterized by spikesof rising gas
• Spicules extend upward from the photosphere into the chromosphere along the boundaries of supergranules
Solar Science Workshop6/8/05
Chromospheric Features:Plages and Filaments• Filaments are dark, thread-
like features seen in the red light of hydrogen (H-alpha). – Dense cooler material
suspended at high altitudes by magnetic fields
• Plage (the French word for beach) are bright patches surrounding sunspots that are best seen in H-alpha. – associated with
concentrations of magnetic fields
Solar Science Workshop6/8/05
Chromospheric Features: Prominences
• Same as filaments, except that they are seen from the side rather than “straight on”
Solar Science Workshop6/8/05
The Corona
• The outermost layer of the solar atmosphere, the corona, is made of very high-temperature gases at extremely low density
• The solar corona blends into the solar wind at great distances from the Sun
Solar Science Workshop6/8/05
The 11-year Sunspot Cycle
Number of Sunspots versus time – they come and go every 11 years
Number of Sunspots versus latitude – forms a “butterfly pattern”
Solar Science Workshop6/8/05
The Maunder Minimum
• Complete absence of sunspots for 50 years corresponds to a mini ice age
• There is a loose correlation between global man temperature and sunspots
Solar Science Workshop6/8/05
These changes are caused by convection and the Sun’s
differential rotation: The Solar Dynamo
Solar Science Workshop6/8/05
The Buildup of magnetic field energy must be released – how?
• Coronal Mass Ejections and Flares– Releases an enormous amount of
energy – A solar flare is a brief eruption of
hot, ionized gases from a sunspot group
– A coronal mass ejection is a much larger eruption that involves immense amounts of gas from the corona
• These storms can interact with the Earth and create huge geomagnetic storms
• They also accelerate particles to very high energies
Solar Science Workshop6/8/05
Coronal loops expand from the surface of the Sun following a solar explosion (solar flare) on April 21, 2002
TRACE movie
Solar Science Workshop6/8/05
Solar Science Workshop6/8/05
The Halloween 2003 Flares were the Largest in Modern History
Perhaps the most extreme flare ever seen erupted on Nov. 4 ...
IMAGES: SOHO/NASA/ESA
... and then this coronal mass ejection was hurled into space.
Solar Science Workshop6/8/05
Solar Science Workshop6/8/05
Aurora The pattern of auroral light around the north and south magnetic poles is called the auroral oval. It expands and contracts over a period of hours and days, depending on geomagnetic activity.
Solar Science Workshop6/8/05
Aurora in Tucson
Solar Science Workshop6/8/05
Shock Waves in Space
• Analogy with sonic booms
• Can accelerate charged particles to very high energies
• Radiation Environment !
• Space Weather