Units 1-5 Vocab Flashcards
Measured Earth’s circumference; used length of shadows cast by sun at noon during the summer solstice at 2 different places.
Eratosthenes
First to suggest that Earth goes around the Sun (heliocentric model)
Aristarchus
Constructed models that could explain retrograde motion. Came up with epicycles to explain retrograde. Assumed the planet rotated about a different point from the earth at a uniform rate. His Earth centered model.
Ptolemy
Created a sun-centered model designed to replace the Ptolemaic models (heliocentric model). He had more quantitative models with actual numbers about the planets’ average distances from the sun. Believed planets orbited in circular motion. Said that if earth was in the center, then we would always see stars rise and set.
Copernicus
He discovered a supernova after he thought he discovered a star. He challenged the unchanging perfect heavens (proved Aristotle wrong). He dodn’t beeive in the heliocentric model. His model had Earth at center of universe. The Sun, moon, and stars revolve around the Earth, but the 5 naked eye planets revolve around the Sun.
Brahe
Thought earth was at the center of the universe, heavens are perfect and unchanging, Earth is subject to decay. Planets, moon, sun, and stars revolve around the Earth in 55 celestial spheres.
Aristotle
Hired by Brahe to analyze his planetary data. He proposed elliptical orbits; orbit of the planets are ellipses with the sun at one of the focus. He formulated 3 laws that describe planetary motion.
Kepler
The orbit of each planet around the Sun is an ellipse with the Sun at one focus.
Kepler’s First Law
As a planet moves around its orbit, it sweeps out equal areas in equal times.
Kepler’s Second Law
More distant planets orbit the Sun at slower average speeds, obeying a precise mathematical relationship (P^2=a^2)
Kepler’s Third Law
First man to point a telescope at the sky; saw shadows cast by the mountains on the moon (it was a place, not a perfect, heavenly body). Discovered planets have their own systems, like Jupiters 4 moons. First to conclude that sunspots are on the sun. Suggested stars are at a large range of distances, not in the same crystalline sphere. Discovered balls of different mass dropped at the same height, take the same times to fall, independent of their mass.
Galileo
Planets usually move eastward through the constellations. Eastward motion is occasionally interrupted by intervals of westward motion. (Apparent Retrograde Motion).
Motion of Planets
Took apparent motions very literally; stars, sun, moon, planets fixed on translucent spheres that rotate around fixed Earth.
Geocentric
Planets revolve around the Sun at the center of the Universe.
Heliocentric
The apparent shifting of an object against the background, due to viewing it from different positions.
Parallax
Closet point in an ellipse.
Perihelion
Farthest point of ellipse.
Aphelion
A type of oval that happens to be the shape of bound orbits.
Ellipse
Small circle upon which a planet moves while simultaneously going around a larger circle (the derent) around Earth in the Ptolemaic model of the universe.
Epicycle
The large circle upon which a planet follows its circle-upon-circle path around Earth in the (Earth-centered) Ptolemaic model of the Universe.
Deferent
Motion that is backward compared to the norm. Ex. Mars during the period of time when it moves westward, rather that the more common eastward, relative to the stars.
Retrograde Motion
An object moves at constant velocity unless a force acts to change its speed or direction.
Newton’s First Law
Force=mass*acceleration
Newton’s Second Law
For every force, there is always an equal and opposite reaction force (along the same line).
Newton’s Third Law
The rate at which an object moves (distance/time) Measured in m/s
Speed
The combination of speed and direction of motion; it can be stated as a speed in a particular direction. measured in m/s
Velocity
The rate at which an object’s velocity changes. Measured in m/s^2
Acceleration
A great island of stars in space, all held together by gravity and orbiting a common center.
Galaxy
The group of about 40 galaxies to which the Milky Way Galaxy belongs.
Local Group
The sky as viewed from a particular location on Earth (or another solid object). Objects in the local sky are pinpointed by the coordinates of altitude and direction (or azimuth).
local sky
The supercluster of galaxies to which the Local Group belongs.
Local Supercluster
The largest known structures in the universe, consisting of many clusters of galaxies, groups of galaxies, and individual galaxies.
Superclusters
the sum total of all matter and energy
Universe
distance that light can travel in 1 year, which is about 10 trillion kilometers (6 trillion miles).
Light-year (ly)
Earth’s average distance from the Sun, which is about 150 million kilometers (93 million miles)
Astronomical Unit (AU)
The portion of the entire universe that can be seen from Earth, at least in principle.
Observable Universe
The spinning of an object around its axis.
Rotation
The orbital motion of one object around another due to gravity.
Orbit
The increase in the average distance between galaxies as time progresses.
Expansion
Matter that we infer to exist from its gravitational effects but from which we have not detected any light; it apparently dominates the total mass of the universe.
Dark Matter
Name sometimes given to energy that could be causing the expansion of the universe to accelerate.
Dark Energy
a region of the sky with well-defined borders
Constellation
the point directly over Earth’s North Pole.
North celestial pole
the point directly over Earth’s South Pole.
South celestial pole
is a projection of Earth’s equator into space, makes a complete circle around the celestial sphere.
Celestial equator
The path the Sun follows as it appears to circle around the celestial sphere once each year. It crosses the celestial equator at a 23 12 ° angle, because that is the tilt of Earth’s axis.
Ecliptic
The boundary between Earth and sky
Horizon
The point directly overhead
Zenith
An imaginary half circle stretching from the horizon due south, through the zenith, to the horizon due north.
Meridian
an object is the angle it appears to span in your field of view.
Angular size
between a pair of objects in the sky is the angle that appears to separate them
Angular Distance
why do the seasons occur?
the tilt of Earth’s axis causes sunlight to fall differently on Earth at different times of year.
the summer solstice in the Northern Hemisphere, occurs around June 21 and is the moment when the Northern Hemisphere is tipped most directly toward the Sun and receives the most direct sunlight.
June Solstice
called the winter solstice in the Northern Hemisphere, occurs around December 21 and is the moment when the Northern Hemisphere receives the least direct sunlight.
December Solstice
called the spring (or vernal) equinox in the Northern Hemisphere, occurs around March 21 and is the moment when the Northern Hemisphere goes from being tipped slightly away from the Sun to being tipped slightly toward the Sun.
March Equinox
called the fall (or autumnal) equinox in the Northern Hemisphere, occurs around September 22 and is the moment when the Northern Hemisphere first starts to be tipped away from the Sun.
September Equinox
a gradual wobble that alters the orientation of Earth’s axis in space.
Precession
the Moon’s appearance in our sky changes as its position relative to the Sun changes (lasts 29 1/2 days)
Lunar phases
Moon rotates on its axis in the same amount of time it takes to orbit Earth
synchronous rotation
If the Sun, Earth, and Moon are nearly perfectly aligned, the Moon passes through Earth’s full shadow
Total Lunar Eclipse
alignment is somewhat less perfect, only part of the full moon passes through the full shadow
Partial Lunar Eclipse
Moon passes only through Earth’s partial shadow (penumbra)
Penumbral Lunar Eclipse
occurs when the Moon is in a part of its orbit where it is relatively close to Earth, the Moon’s full shadow can cover a small area of Earth’s surface
Total solar eclipse
If the eclipse occurs when the Moon is in a part of its orbit that puts it farther from Earth, the full shadow may not reach Earth’s surface
Annular Solar Eclipse
only part of the Sun is blocked from view
Partial Solar Eclipse
the apparent shift of position (parallax) of any nearby star (or other object) against the background of distant stars.
Stellar Parallax
the apparent surface of the heavens, on which the stars seem to be fixed
Celestial Sphere
A star whose complete circle lies above our horizon
Circumpolar star
The angular north-south distance between Earth’s equator and a location on Earth’s surface.
Latitude
The angular east-west distance between the prime meridian (which passes through Greenwich, England) and a location on Earth’s surface.
Longitude
depends on its position relative to the Sun as it orbits Earth
Phase of the moon
when Earth’s shadow falls on the Moon
Lunar eclipse
when the Moon blocks our view of the Sun
Solar eclipse
planetary orbits are not circles but instead are a special type of oval
Ellipse
The long axis of the ellipse
major axis
each half of the major axis
Semimajor axis
a quantity that describes how much an ellipse is stretched out compared to a perfect circle
eccentricity
explaining a thing no more assumptions should be made than are necessary.
Occam’s razor
When a powerful yet simple model makes predictions that survive repeated and varied testing
Theory
The circle on Earth with latitude 23.5°N, which marks the northernmost latitude at which the Sun ever passes directly overhead
Tropic of Cancer
The circle on Earth with latitude 23.5°S, which marks the southernmost latitude at which the Sun ever passes directly overhead
Tropic of Capricorn
mass x velocity
momentum
amount of matter in your body.
mass
the force that a scale measures when you stand on it; that is, weight depends both on your mass and on the forces (including gravity) acting on your mass.
weight
Energy carried by light
radiative energy
Stored energy
potential energy
Energy of motion
kinetic energy
depends on its mass and how far it can fall as a result of gravity
An object’s gravitational potential energy
Orbits on which an object travels repeatedly around another object; bound orbits are elliptical in shape.
Bound orbits
the distance from one peak to the next (or one trough to the next)
wavelength
the number of peaks passing by any point each second.
frequency
Light with very long wavelengths (and hence low frequencies)—longer than those of infrared light.
Radio waves
The spectrum of a traditional, or incandescent, light bulb (which contains a heated wire filament) is a rainbow of color.
Continuous Spectrum
The light that our eyes can see
visible light
A thin or low-density cloud of gas emits light only at specific wavelengths that depend on its composition and temperature. The spectrum therefore consists of bright emission lines against a black background
Emission line spectrum
If the cloud of gas lies between us and a light bulb (and the cloud is cooler than the light bulb or other light source), we still see most of the continuous spectrum of the light bulb. However, the cloud absorbs light of specific wavelengths, so the spectrum shows dark absorption lines over the background rainbow
Absorption line spectrum
summer solstice in the northern hemisphere, occurs around June 21 and is the moment when the NH is tipped most directly toward the sun and receives the most direct sunlight.
June Solstice
Winter solstice in the Northern Hemisphere, occurs around December 21st and is the moment when the NH receives the least direct sunlight.
December Solstice
Spring equinox in the North Hemisphere, occurs around March 21st and is the moment when the NH goes from being tipped slightly away from the sun to being tipped slightly toward the sun.
March Equinox
Autumn equinox in the Northern Hemisphere, occurs around September 21st/22nd and is the moment when the NH first starts to be tipped away from the sun.
September Equinox
Phases of the moon starting a New Moon
New moon, waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, third quarter moon, waning crescent.
