-
solar system
- our sun and all the objects that orbit it
- located a little over halfway from the galactic center to the edge of the galactic disk
-
Milky Way Galaxy
- our disk-shaped collection of stars
- contains more than 100 billion stars
-
galaxy
- great island of stars in space
- contains between a few hundred million to a trillion or more stars
-
local group
the group of about 40 galaxies to which the Milky Way belongs
-
galaxy clusters
- a collection of a few dozen or more galaxies bound together by gravity
- smaller collections of galaxies are simply called groups
-
universe
the sum total of all energy and matter
-
expanding
- the idea that the space between galaxies or clusters of galaxies is growing with time
- caused by the Big Bang
-
nuclear fusion
he process in which two (or more) smaller nuclei slam together and make one larger nucleus
-
light year
the distance that light can travel in 1 year, which is 9.46 trillion km
-
observable universe
the portion of the entire universe that, at least in principle, can be seen from Earth
-
rotation
the spinning of an object around its axis
-
orbit or "revolution"
the orbital motion of one object around another
-
astronomical unit (au)
the average distance (semimajor axis) of Earth from the Sun, which is about 150 million km
-
ecliptic plane
the plane of Earth's orbit around the Sun
-
axis tilt
the amount by which a planet's axis is tilted with respect to a line perpendicular to the ecliptic plane
-
what is your universal address?
universe -> local supercluster -> local group -> milky way galaxy -> solar system -> north america -> USA -> Florida -> Orlando -> Main Campus -> MAP 260
-
our cosmic origins (figure 1.2)
-
constellations
- a region in the sky with well-defined borders
- there are 88 official constellations
-
why do stars rise and set?
- because all stars have daily circles that are partly above and partly below the horizon, they appear to rise and set because Earth rotate from west to east
- stars in the north celestial pole do not rise or set but are circumpolar (make daily counterclockwise rotations)
- stars in the south celestial pole do not rise above the horizon
-
how does latitude affect constellations?
- it affects the locations of the horizon and zenith relative to the celestial sphere
- the altitude of the celestial pole in your sky is equal to your latitude
-
celestial sphere
- the imaginary sphere on which objects in the sky appear to reside when observed from Earth
- 4 points: north celestial pole - south celestial pole - celestial equator - ecliptic
-
Milky Way
- the band of light that circles all the way around the celestial sphere
- it traces our galaxy's disk of stars (the galactic plane) as it appears from our location in the outskirts of the galaxy
-
angular sizes and angular distances
size - the angle it appears to span in your field of view, does not tell us an object's true size, the further the object the smaller the angular size
distance - the angle that appears to separate two objects in the sky
-
what causes seasons?
- the Earth's axis tilt causes sunlight to fall differently on Earth at different times of the year
- has nothing to do with the Earth's distance from the Sun
- Earth's axis tilt is 23.5 degrees, always pointed towards Polaris
-
solstices
- summer (June) solstice - June 21, northern hemisphere receives more direct sunlight that the southern hemisphere, the sun is at its highest at noon
- winter (December) solstice - December 21, northern hemisphere receives its least direct sunlight, the sun is at its lowest at noon
-
equinoxes
- spring (March) equinox - March 21, the moment when the northern hemisphere is being tipped slightly toward the sun
- fall (September) equinox - September 22, the northern hemisphere first starts being tipped away from the sun
- the sun rises precisely due east and sets precisely due west
- the sun falls equally on both hemispheres
-
precession
- the wobble of the earth on it's tilt
- DOES NOT change the earth's tilt (always remains at 23.5 degrees)
- caused by gravity's effect on a tilted rotating object that is not a perfect sphere
-
moon phases (lunar phases)
- half of the moon is always illuminated by the sun, but the amount we see depends on the Moon's position in orbit
- 29.5 days for a complete orbit (new moon - new moon)
-
eclipses
- solar eclipse - when the sun and moon are on the same side, moon casts a shadow on earth, only new moon
- lunar eclipse - when the sun and moon are on opposite sides, earth casts a shado on the moon, only full moon
- there is not an eclipse every moon cycle because the moon's orbit has a 5 degree tilt
- saros cycle - eclipse cycle
-
retrograde motion
the appearance of planets moving "backward" because earth is passing them in its orbit
-
stellar parallax
hold thumb out and close eyes simultaneously
how the Greeks explained retrograde motion
-
what did ancient civilizations build to study astronomy?
- Egyptian obelisk - determined the time of day
- Stonehenge, Templo Mayor (Aztec), Sun Dagger - mark seasons
- Babylonians, Mayans, Muslims - lunar calendar (Metonic cycle every 19 years, eclipse predictions)
-
Plato
idea of perfect circles, perfect spheres, perfect bodies
-
Aristotle
produced first geocentric (earth-centered model) using Plato's ideas of perfect circles
-
Ptolemy
created Ptolemic model, a geocentric model explaining retrograde motion using perfect circles
-
Copernicus
- heliocentric (sun-centered) model
- distances in AU to planets
- perfect circles
-
Tycho Brahe
- naked-eye observations
- earth centered model
-
Kepler
- planets orbit in ellipse
- three laws of planetary motion
-
Kepler's 1st Law
the orbit of each planet about the Sun is an ellipse with the Sun at one focus (planets distance from sun varies during its orbit)
-
Kepler's 2nd Law
as a planet moves around its orbit it sweeps out equal areas in equal times (planets travel faster when its closest to sun and slower when its farther)
*think of ice skater spinning
-
Kepler's 3rd Law
- more distant planets orbit the sun at slower average speeds
- p^2 = a^3
-
Galileo
- non-perfect bodies - Moon has craters, Venus has phases, Jupiter has moons
- used the telescope
- stars were too distant for stellar parallax
-
Newton's 1st Law
object in motion stays in motion unless acted upon by another force
-
-
Newton's 3rd Law
every force is paired with an equal and opposite reaction force
-
law of conservation of angular momentum
- total angular momentum can never change
- m*v*r
- spinning skater
-
law of conservation of energy
energy cannot appear out of nowhere and cannot disappear into nothingness
-
gravity
- strength of the gravitational force attracting any two objects is directly proportional to the product of their masses
- strength of gravity between two objects between decreases with the square of the distance between their centers
- Fg=G M1*M2/d^2
-
orbital energy
sum of its kinetic and gravitational potential energies
-
gravitational encounters
two objects can exchange orbital energy when they pass near enough so that each can feel the effects of the other's gravity
-
atmospheric drag
friction can cause objects to lose orbital energy
-
escape velocity
the speed necessary for an object to completely escape the gravity of a large body such as a moon, planet, or star
-
tides
- high tide is always closest to the moon
- 4 tides per day (2 high tides and 2 low tides)
- spring tides are highest of month (Full and New moon)
- neap tides are lowest of the month (1st and 3rd quater moon)
-
what is light?
- white light is all colors mixed together
- visible light - the light our eyes can see, ranging in wavelength from about 400 to 700 nm
- electromagnetic radiation - another name for light of all types, from radio waves through gamma rays
- light travels in waves and particles (photons)
-
what are the bands of electromagnetic radiation?
- radio band - lowest energy band; fm/am/satellite
- infrared band - heat band; sun warmth on skin
- visible band - band of light you see with your eyes; ROYGBIV, red = low energy, violet = high energy
- ultraviolet band - skin cancer, cataracts, burns and tans
- xray
- gamma ray
-
wave properties of light
- the longer the wavelength the lower the frequency (vice versa)
- wavelength x frequency = speed of light = constant
|
|