The Sun

Basic Properties:

Mass = 332,000 M(Earth)

Equatorial Radius = 109 Earth radii

Surface Temperature = 5780 K

Solar cycle 22 years long

Structure

Luminosity of the Sun

Temperature:

Peak of the Electromagnetic Spectrum occurs at 5780 K (Wien's Law)

Energy/area/s = Stefan's Law

F= sT⁴

^F=5.67x10^-8 W/(m²K⁴) (5780 K)⁴

F=6.32x10⁷ W/m²

W=energy/s=J/s

Over the total surface area of Sun: luminosity=3.85x10²⁶ W

Luminosity of the Sun

Earth intercepts a small amount of the Sun's energy output

Sun's luminosity =3.85x10²⁶W

Earth receives 1400 W/m²

This number is called the Solar constant =1400 W/m²

Luminosity=F · area

Energy

Review Chapter 3 and 4

Wien's Law and Stefan's Law

Solar constant =1400 W/m²

A sunbather with a surface area of 0.5 m² receives

Luminosity=F · area=1400 W/m² x0.5 m²

^Luminosity= 700 W=700 J/s

Energy Transfer

3 Methods of Energy Transfer

Convection- heated material physically moved

Water boiling

Conduction

Heating pad, water bottle

Radiation

Sunshine

Properties of Different Regions

Table 16.1

Temperature of Sun's Atmosphere

Min temp in chromosphere

Fig. 16.13

Sun's Chromosphere

Moon during eclipse blocks photosphere

Fig. 16.10

Sun's Corona

Moon during eclipse blocks photosphere and chromopshere

Fig. 16.10

Granulation

Evidence of convection

Fig. 16.7

Solar Spectrum

What can we learn from Spectrum and lines?

Temperature

Density

Composition

Fig. 16.8

Spectral Line Formation

H and K lines of Calcium

Photons from deep inside Sun are more likely to be reabsorbed

Fig. 16.9

Composition

Sun is mostly hydrogen

91.2 % by number of atoms

71.0 % by total mass

Table 16.2

Oscillation (Seismology) of Sun

In left image, red is moving down, blue is moving up

Fig. 16.4

Interior of Sun

Fig. 16.5 and 16.6