INTRODUCTION TO THE PHYSICS OF THE SUN, HELIOSPHERE AND SPACE WEATHER

Volker Bothmer1 and Jörg Büchner2

1Institute for Astrophysics, University of Göttingen (IAG) 2Max-Planck-Institute for Solar System Research (MPS), Kaltenburg-Lindau

Lectures WS 2010/2011

26 October 2010 – 15 February 2011

1. The Sun

Sketch of the location of the solar system in the milky way

We are somewhere here

Douglas Adams – Hitchhiker‘s Guide to the Galaxy

“Far out in the uncharted backwaters of the unfashionable end of the western spiral arm of the Galaxy lies a small unregarded yellow sun.

Orbiting this at a distance of roughly ninety-two million miles is an utterly insignificant little blue green planet whose ape-descended life forms are so amazingly primitive that they still think digital watches are a pretty neat idea.”

Daily view of the Sun

Structure of the Sun

Energy production in solar

interior:

Three steps of p-p chain:

1) Deuteron production

2) He3 production

3) He4 production

eeDpp 2

32 HepD

pHeHeHe 2433

2 ee

eHep 264 4

Jcm

cmmmcE

p

Hep

112

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10428.0)4(007.0

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kgsM

JsL

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LN

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Basic facts about the Sun (1/2)

Mean distance from Earth

Length of solar radius

Mass

Volume

Density in core

Mean density

Pressure in core

„Surface“ pressure (photosphere)

„Surface“ temperature

Age

Lifetime

Energy output

149,6 Million km ≈ 210 RE

696,000 km ≈ 109 RE

1.989 x 1030 kg ≈ 333,000 ME

1.412 x 1027 m3 (1.3 Mill. Earth)

151300 kg m-3

1409 kg m-3

2.334 x 1011 bar

0.0001 bar

5780 K

ca. 4,55 Billion years

ca. 5 Billion years

3.9 x 1023 kW

Basic facts about the Sun (2/2)

Luminosity

Solar “constant“

Chemical composition

Escape velocity

Period of siderial rotation / w.r.t. Earth

(Carrington, Bartels rotation systems) ! Differential rotation – the Sun rotates faster at the

equator

Time of rotation around galactic center

Next star

Next galaxy

3.854 x 1026 J s-1

1367 W/m2

92.1% Hydrogen

7.8% Helium

0.1% other elements

618 km/s (Earth: 11.15 km/s)

25.4 / 27.3 days

25.7 (0°) – 30.8 (60°) days

2.4 x 108 years

alpha-centauri

Magellanic cloud

Structure of the Sun

The visible variation of

spots on the solar disk,

the photosphere,

reveals that the Sun is

not a perfectly

unchanging object

The Sun in March 2001 - SOHO

SOHO/MDI

Sunspots

dark regions in photosphere =

concentrations of magnetic flux

cooler temperature (T ~ 4000 K; TPh =

5780 K)

magnetic field strength ~ 0.2 - 0.4 T

(2000-4000 Gauß; BEarth ~ 50.000 nT = 10-5 T)

Large sunspots on the solar disk

1 Solar Radius = RS = 696,000 km

1 Solar Rotation = SR = 25.4 Days

From Earth: 27.3 days

Northpole

Southpole

Approx. Size of Earth 1 RE = 6380 km

March 30, 2001 April 2, 2001

MDI HR Field of View (FoV)

Sunspots reveal solar rotation

Galilei, ab 1609 SOHO/MDI

Sunspot records

„Maunder Minimum“

Sunspot number

Sunspot numbers

• Daily "Boulder Sunspot Number," (NOAA SEC):

http://www.ngdc.noaa.gov/stp/solar/ssndata.html

• "International Sunspot Number" from the

Solar Influences Data Center in Belgium:

http://sidc.oma.be/

Rudolph Wolf’s formula (1848):

R: sunspot number

G: number of sunspot groups on solar disk

S: total number of individual spots in all groups

K: variable scaling factor (usually <1) that accounts for

observing conditions and telescope type

Monthly values since 1749

The Boulder numbers are on average 25% higher than the

"International Sunspot Number" because of data from

different observatories.

)10( sgkR

Scheiner, 1625

Sunspot dynamics

Swedish 1 m Teleskop, La Palma, July 2002

However, sunspots do reveal only parts of the photospheric field structure, also information on coronal structure is missing – The Sun at visible and EUV wavelengths

The Sun imaged at different wavelengths on 9th November 2005 (Bothmer & Zhukov 2006)

The Sun is not a perfect black body

For a perfect black body the emission is a function of wavelength depending on

temperature: Planck law of radiation: kλ=hc2/λ5(hc/eλkT – 1)

Solar EM spectrum

Selected literature

• Aschwanden, M., Physics of the Solar Corona, Springer/Praxis,

2009

• Bothmer, V., Daglis, I., Space Weather – Physics and Effects,

Springer/Praxis, 2006

• Lang, K.R., The Sun from Space, Springer-Verlag Berlin

Heidelberg, 2009

• Marsch, E., Schwenn, R. (eds.), Physics of the Inner Heliosphere

I, Springer-Verlag Berlin Heidelberg New York

• Parks, G.K., Physics of Space Plasmas, 2nd Edition, Westview Press

Inc., 2003

• Prölss, G.W., Physics of the Earth's Space Environment, 2nd

Edition, Springer Berlin Heidelberg, 2004

• Schwenn, R., Marsch, E. (eds.), Physics of the Inner Heliosphere

II, Springer-Verlag Berlin Heidelberg New York

• Stix, M., The Sun, an Introduction, Springer Berlin Heidelberg,

2nd Edition, 2002