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

C:\Documents and Settings\youra\My Documents\work\Presentations\talks10\Open day\full_color.mov

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