Including...
The sun is just an ordinary star
Its energy makes all life and surface processes possible
Minor changes in its energy output can have a major impact on the earth
Ice ages are an extreme possibility
Controls the climate
Differential heating of the earth - we've talked about this
Your basic garden-variety star
Not too hot or cold, too big or small
Maybe that's why we have life in our solar system
The sun is so close we can easily study how it works
Study can help us understand how the other stars work
Acts as a "benchmark" for understanding the universe
Composed of essentially 2 elements (98%)
See Table 26.3 pg. 437
Hydrogen: 92% by # of atoms; 73.4% by mass
Helium: 7.8% by # of atoms; 25% by mass
Basically, a large fusion reactor
Running at Warp 97 and out of control
Incredible amount of energy
The inner portions of the sun cannot be studied
The outer layers emit too much energy to see through them
Therefore we can only speculate as to what the inside is like
Possibly a "solid" core? We'll never know
No matter what, it's gotta be pretty hot
15 X 106 °K
DIGRESS TO: bright light
There are 4 general divisions (or layers) to the solar atmosphere
1) The Photosphere
This is the part we see (so to speak)
Not a specific surface, but a range up to 400km in depth
Like you would expect in an "atmosphere"
Pressure and density increase dramatically with depth (table 26.2, pg. 437)
But remain far less than earth atmospheric values
Temperature also increases with depth
4465°K at surface to 7610°K at 400km depth
More than 60 elements have been identified
98% is hydrogen and helium
Most is in elemental (atomic) form
Occasional molecules identified in cooler regions (sunspots)
2) The Chromosphere
Lies immediately above the photosphere
2000 to 3000 km thick
Density decreases upward
Temperature increases upward
From 4500°K at photosphere to 100,000°K at transition to corona
3) The Transition Region
Thin transition from Chromosphere to Corona: 10 to 30 km thick
Actual height above photosphere quite variable
Span "several thousand" kilometers
Very rapid increase in temperature
4) The Corona
The outermost part of the solar atmosphere
Extends for millions of miles above the Chromosphere
Thins to "a sparse wind of ions and electrons" which flows into solar system
Basically the solar wind
Very warm "millions of Kelvins"
Because of the fast particle motion
But very low density
At the base of the corona there are 109 atoms/cm3
As opposed to 1016 in the upper photosphere and 1019 at sea level on earth
Therefore, the actual heat per unit volume is very low
Just not enough particles to do an adequate job of heating things up
Rapid motion doesn't completely answer why the corona (and chromosphere) are so hot
Astronomers assume the sun's magnetic field plays "a major role"
The way magnetism is converted to heat is not at all understood
Sure would be nice to know how this works
The Solar Wind
Stream of "charged particles" flowing out from the sun
Mostly protons - the "ions" mentioned above?
Moving fast - 400 km/sec at earth's orbit
Very sparse - 2 to 10 ions per cubic centimeter!
Earth is protected from these charged particles by the atmosphere
Aurora - interaction of solar wind and the earth's upper atmosphere
Solar Rotation
First identified by watching sunspots move across the surface
Same as the planets - west to east
Axis is tilted like the earth
Different angle - 7° to the plane of the ecliptic (DEFINE)
Since the sun is a gas, it need not act like a solid body
Rate of rotation varies by latitude
25 days at equator; 28 days at 40° north and south; 36 days at 80°
Quite stable in a regional view
Locally, a "seething, bubbling cauldron of hot gas"
And therefore susceptible to the laws of physics which relate to the interaction of things of different temperatures
Granulation (26.9, pg 442)
Surface looks mottled and irregular - not uniformly bright
Appear to be columns of hot gas rising from below the photosphere
With the dark halos site where "cooler" gas sinks back into the sun
Like small convection cells
Not so small - 700 to 1000 km in diameter
Sunspots
Dark, relatively cool regions of the photosphere
Up to 1500° K cooler than the "normal" surface temperature
But still hot enough to toast some weenies and marshmallows
Short-term features - individual spots can last from hours to a few months
Have two different regions (see fig. 26.9, pg. 442)
Umbra - inner darker (and cooler) core
Penumbra - a surrounding less dark (warmer?) area
Can get quite large - up to 50,000 km in diameter
Large groups possible
Usually 2 large spots on E-W line with a cluster of smaller spots around
The occurrence of sunspots follows a definite cycle
Maximum activity at 11.1 year cycle (can vary from 8 to 16 years)
Magnetic fields of the sun
Strongly magnetic near the sunspots - >1000X the earth's
Elsewhere fairly low
When sunspots are grouped, the 2 larger spots will have opposite magnetic polarity
With all the leading spots in each hemisphere having the same polarity - but opposite to each other across the equator
And the next cycle will have the reverse polarity pattern
Results in a magnetic cycle of 22.2 years (2 times the sunspot cycle)
Prominences (page 445)
Usually associated with sunspots and areas of high magnetism
Appear as red, flame-like masses of material rising high above the surface
Can remain stable for hours to days
Very fast moving material - 700 kps to 1300 kps
Flares (page 446)
Short-term high energy emission from sun: Last 5 to 10 minutes
Can be mighty impressive
Release energy equivalent to "a million hydrogen bombs"
Apparently represents release of excess energy caught up in the magnetic field
Can have profound effects on the earth
Would be even more exciting without the atmosphere
Aurora borealis - most obvious effect
Usually occur near earth's magnetic poles
Large solar flares can result in auroras visible at lower latitudes
EX: March 1989 flare caused auroras to be seen in Arizona
Can cause fluctuations in earth's magnetics
Disrupt power lines and damage electrical equipment
EX: same 1989 flare knocked out power in Canada for 9 hours
Can play merry hell with radio, satellite, TV reception
Can actually knock satellites out of orbit and into the atmosphere
Physically (by expanding the atmosphere farther out into space)