1. The Sun: a star close up

2. The Sun in a stellar context: a spectral class G main sequence star

3. The spectral classification system for stars A typical spectral type: M2III Classification for Sun: G2V Stars between G0V and G5V are very similar to Sun Spectral class Number giving more Precise spectral type Luminosity class: III=giant, V=main sequence

4. Other stars in the night sky like the Sun (find them on the pocket Sky Atlas!) StarConstellati on RADecSpectral type BetaCanes Venatici 12h34m+41.5G0V 72Hercules17h21m+32.5G0V 61Ursa Major11h48m+34.0G8V LambdaSerpens15h46m+7.3G0V 16Cygnus19h42m+50.5G3V

5. The Sun: Basic physical properties Mass: 1.989E+30 kg (330,000 mass of Earth) Radius: 696,000 km (109 times than of Earth) Density: 1.5 g/cc

6. Friday question (early today). How do we know that? How do we know the radius (or diameter) of the Sun? How do we know the mass of the Sun?

7. Further properties of the Sun The chemical composition of the Sun: cosmic composition The luminosity of the Sun = 3.85E+26 Watts The age of the Sun (how could we know this?) Comparison of other objects (M4, Arcturus)

8. In contrast to today, there can be sunspots on the Sun Sun of October 30, 2003

9. Structure of a Sunspot Sunspots are regions of very strong magnetic field (2000 Gauss) Demo

10. Solar magnetic fields reach far out into space

11. The 11 Year Solar Cycle The Sun has a “heartbeat”; its properties change on a period of 11 years

12. Latest data on this sunspot cycle

13. The Sunspot Cycle has been going on for a long time Observations show cycle persisting, but “turning off” from 1650 to 1730 (Maunder Minimum)

14. The Structure of the Solar Atmosphere Photosphere Chromosphere Corona Temperature increases as you go up Outermost layer flows out into space to form the Solar Wind

15. The solar corona

16. The Solar Wind A wind past the Earth at 400 km/sec The Sun is “melting away” Density 19 orders of magnitude less than atmosphere A medium for solar events May have “sandblasted” the early atmosphere of Mars

17. The Lesson for Other Stars Do they also have sunspots, sunspot cycles, etc? How does all this (magnetic fields, solar wind, rotation) relate to the age of a star?