ASTRO 7N Unit 3

sun is mostly composed of...

70% hydrogen, 25% helium

2 reasons sun is stable

1. balance of gravity (inward force)
2. gas pressure in hot interior

suns gas pressure from what?

nuclear fusion reactions

suns diameter

109 x earth

suns mass

333,000 x earth

sun luminosity

4x10^24 100 watt light bulbs

% of mass in solar system from sun

99.9%

how long sun been sunning?

4.5 billion years

how long will sun continue to sun?

5.5 billion years

sunspots

slightly cooler regions on sun surface

what sunspots due to

magnetic activity preventing hot material from rising in that region

sunspot cycle?

11 years

nuclear fusion

long lasting energy in stars

proton-proton chain

4 protons combine to make helium-4 (2P & 2N) and release energy in gamma rays

proton-proton chain in depther

1. 2 protons collide @ high speeds and stick together; one changes into a neutron; ends with deuterium nucleus and released energy (1P & 1N)

2. deuterium nucleus from 1 collides with another proton and makes helium-3 nucleus (2P & 1N) and more energy

3. 2 helium 3 nuclei combine to make helium-4 nucleus (2P & 2N)

**NRG RELEASED IN EVERY STEP EVEN THO NEED LOTS OF IT TO BEGIN (E = mc^2)

mass of helium-4 nucleus...

less than mass of 4 protons

layers of sun inside to out

core
radiative
convective
photosphere
chromosphere
flare
prominence
corona
solar wind

core

center; high density and temp
nuclear rxns occur and gamma rays produced

radiative zone

photons repeatedly re absorbed and re emitted
takes long ass time

convective zone

hot gas rises and cold gas sinks
takes like a week

photosphere

"surface" of sun that we see
photons converted to visible wavelengths; can see "granules" due to convection bringing material up and down in cells

chromosphere

red/orange color
we see thru this down to photosphere

flare

eruption coming out of sun due to magnetic activityp

prominence

hoop shaped eruption out of sun due to magnetic activity

corona w/ a lime

low density
visible during solar eclipses

solar wind

charged particle coming from sun's surface escaping to deep space
permeates whole solar system

luminosity

absolute power output at source

brightness

apparent output observed at some distance awau

inverse-square law

determines how bright star appears
based on L and D

parallax method to measure distances

view star from 2 locations on opposite sides of sun (earth 6 months apart - opposite ends of baseline) and look for minute changes in apparent position

stellar parallax measurements

baseline = 1 AU

target star appears to move by and angle _____ times parallax angle

2 two times!!!!!!

why do stars sometimes appear fainter when they are closer than brighter ones?

the brighter one is more luminous

cooler stars are

redder

hotter stars are

bluer

star spectral class from hotter to cooler

O - B - A - F - G - K - M

"only bored astronomers find gratification knowing mnemonics"

how is spectral class determined

using absorption spectrum

closest star

alpha centauri
part of triple star system sim to sun

nearest stars are...

cool and dim
lower right of H-R diagram

brightest star

sirius
binary companion star white dwarf

brightest stars

vary in properities
red and blue
low and high luminosity
all over the freaking place like why

5 properites of a star

luminostiy
mass
size
temp
age

larger star size =

larger light-emitting surface area = greater luminosity

higher star temp =

much greater luminosity and blue peaks

main sequence stars

upper left to lower right on diagram
burning H into He in cores
higher temp = higher luminosity

main sequence red dwarfs

lower right

main seq blue giants

upper left

what determines where main seq star lives?

mass!!

more-massive main seq star are on...

upper left of H-R diagram

more-massive stars use greater fuel supple...

more rapidly

not main stars red giants and supergiants

burning He in core or heavy elements - not H
starting to die :(
large ass size and luminous
TOP RIGHT

not main stars white dwarfs

hot, small and dim
LOWER LEFT

sun history

stellar, protostar, main, red giant, nebula, white dwarf

planetary nebula

ejected envelope (layers outside core) of low to intermediate mass star

white dwarf

end state of former-star's core
held up by gravity and e- presure
SIZE OF EARTH

brown dwarfs

low mass and never heat up enough to have nuclear rxns
FAILED STARS

massive star lives

shorter lives as star mass increases

hydrogen burning for massive stars until what

hydrogen exhausted and then He burning while swelling into red giant

onion skin model

concentric shells of fusion zones involving different chemical elements with heaviest towards core
stops burning around iron bc stable

type 2 supernova

violent explosion with stars core left behind
creates short lived highly energetic environment that can burn HEAVY AF elements

neutron star

city sized

black hole

cores mass less than 3 solar masses
INFINITESIMALLY SMALL RADIUS
left behind after supernova explosion

gravity of black hole

so great that even light cannot escape

event horizon

spherical boundary around black hole from within which nothing can escape not even light L

what is used to measure black holes mass

speed of orbit of star in binary system with a black hole

what is near black hoel?

strong tidal forces

what do strong tidal forces create?

stretched out objects bc force on nearer part greater than force on farther parts

center of black hoel

SINGULARITY - point of infinite density

star begins with mass less than 8 solar masses

core becomes white dwarf - collappse stops bc dengeneracy pressure of elections; core radius same as earth
white dwarf surround by released outer layers (nebula)

8-40 solar masses

final core collaspe preceded by type 2 supernova
core becomes neutron - collapse stops bc degeneracy of pressure of neutrons

greater than 40 solar masses

final core collapse preced by type 2 supernova
core = black hole collapse does not stop SINGULARITY

habitable zone

region around star where liquid could be present on planets surface not too hot not too cold

less massive habitable zone

closer to star

more massive habitable zone

farther from star

drake equation

method to estimate number of communication/technological civilizations in our galaxy at a given time

kepler mission transit method

brightness of star decreases regularly due to planet passing right in front of it
uses 3rd law to find distance