Solar System

2 light years diameter (including Oort cloud)

Sun

9 planets - 39 AU

Approx. 140 moons known today

Approx. 100,000 asteroids

Dust

Billions of comets in 0ort cloud

Kuiper Belt Objects

Meteoroids (cometary and asteroidal fragments)

Sun

- Nearest star - "Above average"

- 4.5 billion years old

- 109 x earth's diameter

- Over 300,000 times as massive

- Density 1.4 x H₂0

- Mostly hydrogen (71%) and helium (27.1%)of mass

Photosphere - 5800K - yellow from Wien's law

- Temp. increases to 10 million+ K @ center

- Gravity tries to compress it; gas pressure opposes collapse

- Hydrostatic equilibrium

- Energy to heat gas to high pressures originates in core: central portion of sun

- Nuclear fusion reactions - lighter elements fuse to form heavier elements

- In sun: 3 step process with release of energy and other particles in different steps

Net reaction: 4 protons (hydrogen nuclei) combine to create 1 helium nucleus + energy - proton-proton chain

Appear dark because cooler 4000K

Stefan-Boltzman law: P ~ T⁴ 1/5 the power of the surroundings .-. dimmer

Associated w /magnetic activity

Splitting of spectral lines: Zeeman effect (lines as doubles or more)

Spots often in pairs, one north magnetic pole, other south mag. pole

Rotational axis 7 deg off perp. to ecliptic

Solar Flares: hot gas, radiation

- erupt from around sunspots

- most violent solar activity

- charged part., visible, x-ray, ultraviolet

- follow magnetic field lines out of sunspots

- cause auroras, radio interference

Solar cycle: of sunspots and solar activity in general run on 11 yr. cycle max. to max.

- also, sunspot pairs reverse magnetic polarity every other solar cycle - 22 yr. cycle

- Maunder minimum: 70 yr. period about 1645-1715

- virtually no sunspots, auroras, i.e., none of usual indications of solar activity

- indirect evidence: ¹⁴C high in tree rings

- chaotic weather recorded (cause not known)

Chromosphere: Pink layer above photosphere, 6000 km thick

- seen during solar eclipse

- upper part bristles with jets or spikes of hot gas spicules

- temp. 6,000K - 50,000K

- Transition Zone: between chromosphere and corona

- temp. rises abruptly

Corona: Temp. - 2 million K but gas very tenuous (thin)

visible during s. eclipse

extends to at least 1.5 million km from sun

Solar Wind: Shock waves from photosphere propel outer corona away from sun to create

solar wind - high velocity flow of charged particles reaching to outer solar system.

Prominences: Hugh arch-like structures of relatively Cool gas seen projecting from limb (edge) of sun.

erupt from surface upward into corona - 1 million km

can last months

called filaments when seen silhouetted against surface