January 22, 2014-------------1.1 Our Modern View of the Universe

Basic defintions: o Star – large, glowing ball of gas that generates heat and light through nuclear fusion o Planet – 1) orbits a star; 2) large enough for own gravity to make it round; 3) cleared its orbital path

If it doesn’t satisfy #3, it is a dwarf planet (e.g. Pluto)o Moon (satellite) – orbits a planet (satellite orbits anything) o Asteroid – small rocky, orbits staro Comet – small icy, orbits staro Small solar system body – orbits star but too small to be planet or dwarf planet

What is our place in the universe?o Solar system – the Sun and all the objects that orbit it o Galaxy – great island of stars in space; Milky Way Galaxy o Galaxy clusters – groups of galaxies with more than a few dozen members; Local Group o Superclusters – regions in which galaxies and galaxy clusters are most tightly packed o Universe – sum total of all matter and energy

How did we come to be? o Big Bang and the Expanding Universe – the beginning was the Big Bang and the universe has expanded

since then, but not the individual galaxies, etc. (4.5 billion years ago) o Stellar Lives and Galactic Recycling – stars live as long as they can perform nuclear fusion, when they

exhaust usable fuel they become a supernova and collapse o Stars Manufacture the Elements of Earth and Life – stars convert gases such as carbon, nitrogen, oxygen

and iron How can we know what the universe was like in the past?

o Because when we look at other stars, we see them as they were in the past because it takes x amount of years for the image to reach us.

Can we see the entire universe? o No. We can see the observable universe or approximately 14 billion light years away.

1.2 The Scale of the Universe

1.3 Spaceship Earth How is earth moving in our solar system?

o Rotation (spin) around its axis daily (west to east, counterclockwise when viewed from NP) o Orbit (revolution) around the sun yearly

Astronomical Unit (AU) – average orbital distance, ~150 km Elliptic plane – defined by earth’s orbital path

o Axis tilt (23.5 degrees) from the perpendicular to the elliptic plane oriented to the North Star Polaris Solar system and galactic rotation occurs

1.4 The Human Adventure of Astronomy

January 24, 2014-------------2.1 Patterns in the Night Sky

What does the universe look like from Earth?o Constellations – a region of the sky with well defined borders (which happen to encompass certain patterns

of stars) o The Celestial Sphere – imaginary sphere surrounding earth

North celestial pole – point directly over Earth’s North Pole South celestial pole – point directly over Earth’s South Pole Celestial equator – projection of Earth’s equator into space Ecliptic – the path the sun follows around the sphere once a year, crosses the CE at a 23.5 degree

angle (tilt of Earth’s axis) o The Local Sky = the half of the celestial sphere you see at any time (as seen from where you are standing)

Horizon – boundary between earth and sky Zenith – point directly overhead Meridian – imaginary half circle from S to N through the zenith

Position determined by direction and altitude o Angular Sizes and Distances

Angular size – the angle it appears to span in your field of view Angular distance – the distance that appears to separate them

Arcminutes and arcseconds Why do stars rise and set?

o Stars relatively near the NCP remain perpetually above the horizon; never rise or set but make CCW circles around NCP = circumpolar stars

o Stars near SCP never rise above horizon at allo Other stars seem to rise in E and set in W because of earth’s rotation

Why do the constellations we see depend on latitude and time of year? o Variation with latitude

Latitude = N-S position; 0 at equator; 90 N at NP; 90 S at SP Affects the locations of the horizon and zenith relative to the celestial sphere The altitude of the CP in your sky is equal to your latitude

Longitude = E-W; 0 along Prime Meridian o Variation with time of year

Due to orbit around the Sun Zodiac constellations – constellations along the ecliptic (technically there are 13)

3.1 The Ancient Roots of Science Used by all humans and ancient societies for practical purposes (harvest, climate, etc.) What did ancient civilization achieve in astronomy?

o Determining the time of day through sun dials, moon phases, star and water clocks o Marking the seasons through alignment of buildings or temples (Stonehenge) o Lunar calendars o Archaeoastronomy – study of ancient structures that served astronomical purposes

3.2 Ancient Greek Science Modern scientific roots in Greece: 1) non-supernatural explanations; 2) mathematical precision; 3) reasoning from

observations o Models of nature

How did the Greeks explain planetary motion? o Geocentric model – the Earth at the center with everything else orbiting around it (proposed by Thales,

Plato and Aristotle) in nested spheres Ptolemaic model – each planet moves around the earth on a small circle that turns upon a larger

circle

3.4 The Nature of Science Scientific method

o Hypothesis – tentative explanation, educated guess o Occam’s Razor – simplicity is key o Verifiable observations

Paradigm – school of thought

January 27, 2014--------------3.3 The Copernican Revolution

Challenge to the earth centered model o Copernicus – the Sun is the center and earth revolves around it o Tycho Brahe – naked eye observations; but claimed the sun orbits earth while all other planets orbit the

sun o Kepler – abandon the idea of circular orbits, elliptical ones

Kepler’s three laws of planetary motion o 1) the orbit of each planet around the sun is an ellipse with the sun at one focus

Perihelion – the closest point to the sun Aphelion – the farthest point from the sun

o 2) as a planet moves around its orbit, it sweeps out equal areas in equal times

o 3) more distant planets orbit the sun at slower average speeds, obeying p2 = a3 where p = planet’s orbital period in years and a = average distance from the Sun in AU

Galileo helped solidify Kepler’s observations by using a telescope

4.1 Describing Motion: Examples from Daily Life Speed = how far in a certain amount of time Velocity = speed and direction Acceleration = change in velocity (incl. direction)

o Of gravity = 9.81 m/s2

o Torque = angular acceleration Momentum = mass*velocity

o Angular momentum = m*v*R, where R = distance to object o Momentum and energy are conserved

Force = mass*acceleration (only way to change an object’s momentum) o Of gravity = GMEm/R2

4.2 Newton’s Laws of Motion 1st Law: an object moves at a constant velocity if there is no net force acting upon it

o An object at rest remains at rest and an object in motion remains in motion until something acts upon it 2nd Law: F = m*a 3rd Law: for any force, there is always an equal and opposite reaction force

o Objects always attract each other through gravity

4.3 Conservation Laws in Astronomy Conservation of momentum – the total momentum of interacting objects cannot change as long as there is no

external force acting upon them; it is conserved Conservation of angular momentum – as long as there is no external torque, the total angular momentum of a set of

interacting objects cannot change o Rotating objects will continue to rotate

Conservation of energy – cannot be created or destroyed, only transformed o Kinetic (thermal, aka temperature) o Radiative o Potential

Gravitational potential (mgh near earth’s surface) Mass-energy (E = mc2)

4.4 The Universal Law of Gravitation What determines the strength of gravity?

o Every mass attracts every other mass through gravityo Strength of gravitational force is directly proportional to masses

FG = GM1M2/R2 where G = 6.67*10-11 m3/kgs2

Extension of Kepler’s Three Laws: o Planets are not the only thing with elliptical orbits o Ellipses are not the only possible orbital paths o Objects orbit their common center of mass

Common center of mass – the point at which both stars have the same mass o Orbital characteristics tell us the masses of distant objects

Modification of Kepler’s 3rd Law to be: p2(M1 + M2) = a3

January 29, 2014--------------2.2 The Reason for Seasons

The combination of Earth’s rotation and orbit also leads to the progression of the seasons What causes the seasons?

o The tilt of Earth’s axis causes sunlight to fall differently on Earth at different times of year NHemisphere toward sun in June, away in December

Steeper angle: more concentrated sunlight = warmer, longer and higher path in sky (more day) = summer

Shallower angle: less concentrated sunlight, shorter lower path = winter SHemisphere toward sun in December, away in June

o Gradual change in sunlight angle results in fall and spring o Solstices and equinoxes

Summer solstice (June 21): NHemisphere most toward sun Winter solstice (December 21): NHemisphere most away from sun Spring equinox (March 21): slightly away tip to slightly toward Fall equinox (September 22): becomes slighter away tips

Precession – the gradual wobble of orientation of earth’s axis in space

S1.1 Astronomical Time Periods How do we define the day, month, year, and planetary periods?

o The length of the day Sidereal day: how long it takes for any star to go from its highest point in the sky to its highest

point the next day, approximately 23h 56m; earth’s precise rotation period Solar day: the time it takes for the sun to make one circuit around the local sky; approximately 24h

± 25so The length of the month – as determined by moon

Synodic month: 29.5 day cycle of phases; time it takes for sun and moon to meet in same place Sidereal month: 27.33 days; how long it takes the moon to complete an orbit relative to the

positions of distant stars o The length of a year

Sidereal year: Earth to complete one orbit relative to the star Tropical year: time from the spring equinox of one year to the next; 20m shorter than sidereal yr.

Because of axis precession o Planetary periods

Sidereal period: time it takes for the planet to orbit the sun Synodic period: time when it is lined up with our sun in the sky at one time and the next similar

alignment How do we tell the time of day?

o Apparent solar time – based on the sun’s actual position in the sky o Mean solar time – based on 12:00 noon being the time the sun crosses the meridian on average

Varies due to the analemma o Standard time – divides into time zones, the mean solar time is that of the middle of the zone o Daylight savings time is +1 hour ahead of standard time o Universal time is the time at the prime meridian (Greenwich mean time)

When and why do we have leap years? o Because our calendar is based on the tropical year o Introduced by Julius Caesar in the Julian calendar; every 4th year has 366 days so that the average calendar

year is 365.25 days Pope Gregory XIII Gregorian calendar: leap year is skipped when the turn of the century can be

divided by 4 (e.g. 2100 will not be a leap year) Makes the calendar year almost the same as an actual tropical year

January 31, 2014 --------------2.3 The Moon, Our Constant Companion

Why do we see phases of the moon? o Depends on its position relative to the sun as it orbits earth o Moon spins CCW but we always see the same side of the moon because it rotates at the same rate as Earth

Also known as synchronous rotationo Phases:

New Full New moon Waxing crescent First quarter Waxing gibbous Full moon Waning gibbous Third quarter Waning crescent

What causes eclipses? o Shadows cast by the alignment of the sun, earth and moon

Lunar eclipse: earth directly between sun and moon so that earth’s shadow falls on the moon Solar eclipse: moon directly between sun and earth so that moon’s shadow falls on earth

o Conditions for eclipses Moon’s orbit slightly inclind by about 5 degrees to the ecltipic plane Will spend time either above or below the surface, only crossing twice per orbit (nodes) For an eclipse to occur:

Phase of the moon must be full (lunar) or new (solar) New or full moon must occur when nodes of moon’s orbit are aligned with the sun and

the earth Regions of shadow

Umbra – sun completely blocked Penumbra – sun partially blocked

4.5 Orbits, Tides and the Acceleration of Gravity How do gravity and energy allow us to understand orbits?

o Orbital energy – kinetic and GPE, because nothing acts on it, will always stay the sameo May change through gravitational encounters, when the gravitational force of something else acts on ito Atmospheric drag – may slow things down o Escape velocity – the velocity needed to get out of an orbit, ex: (2GME/R)^(1/2)

How does gravity cause tides? o The tidal effect of the moon

The gravity from the moon becomes weaker as the distance from the moon is greater Difference in attraction causes “stretching force” or tidal force

o The tidal effect of the sun Sun also exerts gravity, but the much greater difference in distance makes pull relatively small Tidal caused by sun is less than half that caused by moon

When they act is same way = spring tides, large When they counteract = neap tides, small

Why do all objects fall at the same rate? o Because their acceleration depends on the distance between center of the object and the earth’s center,

which is pretty much equal

February 3, 2014---------------5.1 Light in Everyday Life

How do we experience light?o Energy and Power

Power = rate of energy flow, measures in watts (1 joule/s)o Light and Color

Spectrum – rainbow of light, split into individual colors produced by diffraction grating or prism How do light and matter interact?

o Emissiono Absorption o Transmission o Reflection/scattering

5.2 Properties of Light Both a particle and a wave

o Definitions: Wavelength = distance from one peak to another Frequency = number of peaks passing by any point each second

Measured in cycles per second, or Hz Speed = how fast they travel Wavelength*frequency = speed

o Light as an electromagnetic wave Electric and magnetic fields

o Photons: “particles” of light Packets of energy

What is the electromagnetic spectrum? o By wavelength (short long)

o Gamma o X-ray o Ultraviolet o Visible

From shortest longest (colors) Violet Indigo Blue Green Yellow Orange Red

o Infaredo Radio

Microwaves in between radio and infared

5.3 Properties of Matter