ast test 1

• 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

• our disk-shaped collection of stars
• contains more than 100 billion stars

• great island of stars in space
• contains between a few hundred million to a trillion or more stars

the group of about 40 galaxies to which the Milky Way belongs

• a collection of a few dozen or more galaxies bound together by gravity
• smaller collections of galaxies are simply called groups

the sum total of all energy and matter

• the idea that the space between galaxies or clusters of galaxies is growing with time
• caused by the Big Bang

he process in which two (or more) smaller nuclei slam together and make one larger nucleus

the distance that light can travel in 1 year, which is 9.46 trillion km

the portion of the entire universe that, at least in principle, can be seen from Earth

the spinning of an object around its axis

the orbital motion of one object around another

the average distance (semimajor axis) of Earth from the Sun, which is about 150 million km

the plane of Earth's orbit around the Sun

the amount by which a planet's axis is tilted with respect to a line perpendicular to the ecliptic plane

universe -> local supercluster -> local group -> milky way galaxy -> solar system -> north america -> USA -> Florida -> Orlando -> Main Campus -> MAP 260

• a region in the sky with well-defined borders
• there are 88 official constellations

• 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

• 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

• 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

• 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

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

• 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

• 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

• 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

• 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

• 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)

• 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

the appearance of planets moving "backward" because earth is passing them in its orbit

hold thumb out and close eyes simultaneously

how the Greeks explained retrograde motion

• 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)

idea of perfect circles, perfect spheres, perfect bodies

produced first geocentric (earth-centered model) using Plato's ideas of perfect circles

created Ptolemic model, a geocentric model explaining retrograde motion using perfect circles

• heliocentric (sun-centered) model
• distances in AU to planets
• perfect circles

• naked-eye observations
• earth centered model

• planets orbit in ellipse
• three laws of planetary motion

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)

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

• more distant planets orbit the sun at slower average speeds
• p^2 = a^3

• non-perfect bodies - Moon has craters, Venus has phases, Jupiter has moons
• used the telescope
• stars were too distant for stellar parallax

object in motion stays in motion unless acted upon by another force

F=ma

every force is paired with an equal and opposite reaction force

• total angular momentum can never change
• m*v*r
• spinning skater

energy cannot appear out of nowhere and cannot disappear into nothingness

• 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

sum of its kinetic and gravitational potential energies

two objects can exchange orbital energy when they pass near enough so that each can feel the effects of the other's gravity

friction can cause objects to lose orbital energy

the speed necessary for an object to completely escape the gravity of a large body such as a moon, planet, or star

• 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)

• 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)

• 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

• the longer the wavelength the lower the frequency (vice versa)
• wavelength x frequency = speed of light = constant