RecapRecap

SESAME Astronomy 2011Week 8

SESAME Astronomy 2011Week 8

What we’ve covered

The cause of the seasons

The cause of the moon phases

The solar system

The Sun

Stars

The Cause of the SeasonsEarth orbits Sun

Earth’s rotation axis is tilted relative to orbit

at one side of orbit Northern hemisphere is tilted toward sun, 6 months later Northern hemisphere is tilted away from sun

Tilted toward: longer days, sun higher in sky (direct/concetrated sunlight), tilted away: shorter days, sun lower in sky (indirect/watered down sunlight)

Cause of moon phases

moon orbits earth

exactly half of moon (side facing sun) is always illuminated

relative position of earth-moon-sun determines phase

different phases rise/set at different “times” of day (know which phases rise/set/are highest at which times)

The Solar System

Arrangement

Contents

Formation

What’s in solar systemSun at center, planets orbit it

inner planets are rocky, outer planets are gaseous (why?)

in between Mars and Jupiter is asteroid belt

outside orbit of Neptune are Kuiper belt and Oort cloud

The solar system

Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune

Which planets have moons?

Be able to say one unique thing about each planet

FormationStarted as large gas cloud VERY SLOWLY rotating

collapsed, heated up, spin sped up, became a disk

small clumps grew into bigger clumps, which grew into planets

planets “cleared their orbits” either accreted or kicked out all debris/gas/dust

center of cloud became the sun

The Sunour starfuses H → He in coredifferential rotation: at poles rotation period is 33 days, at equator it’s 25 dayssunspots caused by magnetic fields poking through “surface”sunspot cycle: few sunspots at mid-lattitudes → lots of sunspots at equator → field flips and cycle starts againfield poking through surface → sunspots, prominences, and flares

Coming up:Planetarium trip: THIS SUNDAY 2pm

Homework from chapters

Take-home “final” - pick up Week 10

Sun project - turn in Week 10

Moon project - turn in Week 10

What to look forward to

Constellations

Galaxies

The Big Bang Theory

Stars

Stellar lives

Stellar deaths

Stellar corpses

Stellar livesStars can have masses in the range 0.08M⊙ - 120 M⊙ (why this range?)

Mass determines temperature, which determines color and lifetime

MANY MORE low-mass stars (M < 8-10M⊙) than high-mass (M > 8-10M⊙)

Stellar deaths: low-massrun out of H in core, core shrinks and heats up: expands outer layers into Red Giant, ignites H-shell fusion, (eventually) ignites He-core fusion

He in core runs out, core shrinks, expands outer layers, pushes them off (they are a planetary nebula)

VERY HOT CO core is white dwarf, cools slowly

Stellar deaths: high massruns out of H in core, core shrinks and heats up, ignites He fusion in core and H-shell fusion around core

runs out of He in core, core shrinks and heats up, ignites He-shell fusion and C core fusion

runs out of C in core, core shrinks and heats up... until core is made of iron

(can’t get energy out of iron - why not?)

Stellar deaths: high mass

iron shrinks and heats up, breaks into He nuclei

He nuclei break into P’s and n’s (still shrinking)

e’s and p’s get squeezed into n’s (still shrinking)

core is now just neutrons and outer layers begin to collapse

shrinking core caused fusion shells to expand - outer layers hit expanding fusion shells and explode

Stellar deaths

high-mass stars ALWAYS end in a Type II Supernova -> make lots of “alpha elements”

low-mass stars COULD become a Type Ia Supernva under the right conditions (what are they?) -> make lots of iron

Stellar corpses

low-mass corpse: white dwarf

high-mass corpse: neutron star or black hole