The Sun
Youra Taroyan
Age 4.5 ×109 years Mean diameter 1.392×106 km, 109 × Earth
Mass 1.9891×1030 kg, 333,000 × Earth
Volume 1.412×1018 km3, 1,300,000 × Earth
Motivation
1. Understanding how the Sun affects the Earth and the near space environment (Space weather)
2. The Sun as a star
3. Natural plasma laboratory
The H-R diagram
•Stars fall into concentrated
groups in the H-R diagram
•Each concentration
defines a particular class
•Why white dwarfs or red giants?
Unlike any other star, we can
observe the Sun in detail
The atmosphere of the Sun viewed by
the SDO spacecraft in various channels
which cover temperatures from 5000K to 15MK. All
of these structures are moving
Plasmas
99% of the known
universe is in plasma
state
Looking inside the Sun
“The singing Sun”In the 1960s it was suggested that sound waves could travel around
the inside of the Sun, being reflected at the surface and refracted by the changing density and temperature inside the Sun
These waves can interfere to produce standing waves in the Sun, moving areas of the surface in and out – and this produces small (but
measurable!) Doppler-shifts in the wavelengths of the Sun's light
All modes 1 mode 3 modes
Solar material is hot and structured into different layers with different properties.
The Sun contains a layer which acts as a dynamo, generating a strong magnetic field
Sun doesn't rotate as one massBreakdown in rigid rotation near base of
convection zone (tachocline)Different variation in rotation rate with depth
at different latitudesBands of high- and low-speed flow at different
latitudes and depths in the Sun These bands move over time
Galileo’s drawings of sunspots
The 11-year solar cycle
http://umbra.nascom.nasa.gov/images/latest.html
Increasing temperature
Sun shows more structure (more complexity) at higher temperatures
Sun isn't as simple as it looks in white-light images
Chromosphere - the "coloured sphere"
Seen during total eclipse (or in H- line)
Thin layer ~ 2000 km deep
Temperature ~ 6000 K at base, increases
with height to 20000 K
Low density
Glows red (Hydrogen-
emission)
Chromosphere is hotter than Photosphere - how?
Probably heated by sound waves from
photosphere
Filaments and ProminencesTwo names for the same thing
On the disc of the Sun:Dark channels – Filaments
Relatively cool, dense gas suspended above the chromosphere
Off the limb of the Sun:See the loop of material against the sky
Bright suspended Prominences
May erupt!
Fine-scale structures above the solar limb – Hinode imager
XIX century drawings of a solar eclipse
The Solar Corona
Coronal heating problem
Coronal Loops
Solar minimum and maximum