Evolving Universe

ecliptic

apparent yearly path of Sun across the sky

Wanderers

objects that move differently from the rest of the sky

Erastothenes

Earth’s circumference in shadow angles

Aristarchus

Determine relative sizes and distances, heliocentric

Ptolemy

epicycles, Mercury and Venus

Galilei

Mountains Moon, moons Jupiter, phases of Venus

Celestial equator

Projection of Earth’s equator onto the sky

Right Ascension

East-west position celestial equator (latitude)

Declanation

North-south position (longitude)

Degree Earth’s rotation axis

23.5

Precession

Earth’s rotation axis not fixed

Analemma due to

tilt of Earth’s axis, orbit non-constant speeds (second law Kepler)

Why summer?

Light more concentrated, longer days

Synchronous rotation

Moon always shows same hemisphere towards earth

Tides explained by

Differential gravity

Spring tide (larger tidal range)

Sun and Moon align

Neap tides (smaller tidal range)

Sun and Moon at right angles (first/third quarter)

Lunar eclipse happens at

Full moon

Solar eclipse happens at

New moon

Annular eclipse

Umbra does not reach the Earth

Sidereal

Relative to stars

Synodic

Relative to the Sun

Earth’s density, core

5.52 g/cm³, iron-nickel

What is light?

Electromagnetic phenomenon

Photon energy depends on

Photon frequency

Shorter wavelengths carry…

…more energy per proton

Wien’s law

Peak wavelength, determines temperature

Lyman series

to n=1, UV

Balmer series

to n=2, visible

Paschen series

n=3, infrared

Emission

if gas is thin/hot, gives emission lines

Absorption

if cooler gas lies in front of continuous source, gives absorption lines

Transmission

Light passes through medium

Reflection/scattering

Important in dust clouds, light redirected

Continuum shape (Planck curves) gives

the temperature via Wien’s law

Velocities are measured by

Comparing observed wavelengths to laboratory wavelengths

3 functions of telescope

Light collection, angular resolution, magnification

2 main types of optical telescopes

Refractor telescopes, reflector telescopes

Disadvantage refractor telescope

Chromatic aberration

M=

f lensw/f eyepiece

Light collected proportional to

diameter squared

Adaptive optics

Correct atmopsheric distortion in real time (using reference star and deformable mirror)

Interferometry

Combine signals from many radio dishes

Definition planet

Orbit Sun, be nearly round, cleared its orbital neighborhood

Asteroids

Rocky or metallic, in belt between Mars and Jupiter

Comets

Icy “dirty snowballs” (originally from Kuiper belt or Oort cloud)

Dust tail

Curved

Ion tail

Straight, away from Sun

Proton-proton chain

Nuclei —> helium

Hydrostatic equilibrium

Inward pull of gravity balanced by outward pressure hot gas and radiation in core

Energy transport inner region

Radiation (100s of years)

Outer layer

Convection (rising and sinking of hot gas)

Conduction

Granulation pattern

Photosphere

Visible outer layer, source of most sunlight

Chromosphere

Thin layer visible during eclipses, spicules and prominences

Corona

Outermost layer, extremely hot, source of solar wind

STefan-Boltzmann law

Relates luminosity to temperature and surface area

Spectral sequence (hot to cool)

OBAFGKM

Luminosity depens on

Surface temp and radius

Infrared observations reveal

Warm dust grains

Radio observations

Cold atomic gas, 21-cm emission line of neutral hydrogen

Giant Molecular Clouds

Coldest, densest regions. Primary sites of star formation

<0.08 SM

never ignite hydrogen fusion, brown dwars

L proportional to

M³

<1.5 SM

Proton-proton cycle

More massive stars

CNO cycle

Stellar thermostat

Self-regulating temperature of star

Binary systems white dwarfs ingetion

Nova

White dwarf mass >1.4 SM

Type 1a supernova

>4 SM

Type II Supernova, shock wave

Remaining core >3 SM

Black hole

Milky Way

Spiral galaxy, thin rotating disk, bulge, halo

Population I star

young, metal rich

Spiral arms

young, massive O- and B-type stars, active star formation

Spiral galaxies

Late-type galaxies, gas and dust, spiral arms sites of active star formation

Elliptical galaxies

Early-type galaxies, smooth, no gas and dust, reddish

High-density environments

Elliptical galaxies dominante

Morphology-density relation

Galaxy evolution shaped by internal and external processes