The Sun & The Stars Astronomy Midterm 2

The sunspot cycle

sun’s magnetic poles switch every 11 years between the north pole and the south pole

Solar flares

happens when the suns magnetic field twists up that the pressure makes it explode

• energetic explosions, if its too energetic corona mass ejections happen

Parallax

How astronomers determine distance

• The further something is, the less it moves

• Bigger distance: smaller angle

• Parallax is bigger when it’s close

• P∝ 1/d , or d ∝ 1/p

Parasec

The measure of distance

• Twice as far = ½ as big

• we use this more than light years

The inverse square law

The amount of energy emitted in a span of time is spread out over a larger and larger sphere as light travels away from a star

• Energy per time per area ∝ 1/r²

• If we know a star’s apparent brightness, and its distance from us, we can calculate its luminosity

apparent brightness

how bright a star appears when viewed from earth

• determined by the luminosity but also on the distance of the star

• Apparent brightness ∝ luminosity/d²

luminosity

a measure of the total rate at which a star

• measured in units of energy per second

• from inverse square law

Dark spots

show that atoms absorbed different lights

Hotter stars

Blue

• blue light

• hotter = patterns change

• have fewer features because of the heat

Cooler stars

Red

• red light

• dark features are deep and wide bc of the absorptions are by molecules

Ideal thermal emitters

Opaque objects give off blackbody radiation (photosphere)

• Wien’s law: peak wavelength ∝ 1/T

  • blue stars is hot

  • red star is cold

• Stefan’s law: intensity ∝ T^4

  • curve being higher when we turn up the temperature

Stellar Temperatures

A star with higher temperature will always give off MORE energy at SHORT wavelengths compared to long wavelengths

Stellar types from HIGHEST to LOWEST

OBAFGKM

• hottest to coldest

• Strength of absorption depends on elemental composition, density, and temperature

When was helium created

after the big bang

• the sun is mostly hydrogen (92%) and helium (7%)

L-R-T relation

Luminosity ∝ radius² x temperature^4

• R ∝ L^1/2 x T^-2

• T ∝ L^1/4 x R^-1/2

• BIGGER TEMPERATURE = BIGGER LUMINOSITY