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star

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a sphere of gas shining under its own power

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light year

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the distance light travels in a year

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nebula

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any "fuzzy" astronomical object

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latitude

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angular distance north or south of the equator (parallels)

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longitude

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angular distance around the Earth, measured along the equator

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horizon

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the boundary that divides what you can and can't see in the sky

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celestial sphere

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imaginary sphere centered on the center of the Earth to which it appears the stars are affixed

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conceptual scheme

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a model used to explain observations

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elevation

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the number of degrees above the horizon that an astronomical object is

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zenith

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the point directly above the observer (elevation of 90 degrees)

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celestial poles

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points about which the celestial sphere appears to rotate; intersections of the celestial sphere with the Earth's polar axis

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celestial equator

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a greater circle on the celestial sphere 90 degrees from the celestial poles; where the celestial sphere intersects the plane of the Earth's equator

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Polaris (North Star)

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star at the zenith of the North Pole

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circumpolar stars

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stars that never rise nor set, but just circle around a celestial pole, above the horizon at all times

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planets

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"wanderers"

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ecliptic

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apparent annual path of the sun on the celestial sphere

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constellation

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one of 88 sectors into which astronomers divide the celestial sphere

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asterism

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an especially notable star pattern in the sky (ie. Big Dipper)

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zodiac

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a belt around the sky about 18 degrees wide, centered on the ecliptic

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retrograde motion

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the apparent motion of a planet when it appears to move 'backward' from the direction it normally moves with respect to the stars

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parallax

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the apparent displacement of an object caused by a change in the position from which it is viewed; the closer the object, the greater the parallax

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cosmology

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the study of the universe as a whole: its contents, structure, origin, evolution, and ultimate fate

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geocentric

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explanation of the Sun's apparent motion in which the Sun circles around the Earth once per year

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heliocentric

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explanation of the Sun's apparent motion in which the Earth circles around the Sun once per year

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Aristotle

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very influential Greek philosopher who presented arguments in favor of Earth having a spherical shape (~325 BC)

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eclipse

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the passing of one body into the shadow of another

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lunar eclipse

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the phenomenon that occurs when the moon moves into the shadow of the Earth

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Eratosthenes

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Greek astronomer, mathematician, and geographer who, in ~200 BC, successfully estimated the circumference of the Earth

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epicycle

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a small circle riding on a large circle on which the planet moves

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Plato

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believed in a spherical, centered Earth (~360 BC)

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Claudius Ptolemy

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wrote the Almagest, promoting the idea of epicycles (LIAR!) (~140 AD)

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Aristarchus

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believed the Earth moved around the Sun, but could not prove it and his model was not accepted (~280 BC)

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solar system

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the system of the sun, planets, and other objects revolving around the Sun

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Copernicus

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first to formulate a comprehensive heliocentric cosmology which displaced the Earth from the center of the universe, wrote De revolutionibus (1473-1543)

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De revolutionibus (orbium coelestium)

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"On the Revolutions of the Celestial Spheres," written by Copernicus, published just before his death in 1543

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telescope

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an instrument that collects light and makes distant objects appear larger

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Galileo

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Italian astronomer and mathematician who was the first to use a telescope to study the stars; demonstrated that different weights descend at the same rate; perfected the refracting telescope that enabled him to make many discoveries (1564-1642)

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astrology

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the study of the possible influence that the locations of the sun, planets, and moon in our sky have on human affairs and destiny

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Hipparchus

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perhaps the greatest observational astronomer of ancient times (~150 BC), responsible for creating a precise star catalog (locations and brightnesses) and discovering the precession of Earth's axis

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precession (of Earth's axis)

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the slow conical motion of Earth's axis of rotation, which causes the location of the celestial poles to trace out circles on the celestial sphere, completing one circuit every 26,000 years

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(Galileo's) Law of Inertia

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every body tends to continue doing what it is already doing - being in a state of rest, or moving uniformly in a straight line - unless it is compelled to change by an outside force

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Galileo's Principle of Equivalence

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there is no way to tell locally the difference between being in a reference frame that is at rest or one that is moving at a constant speed in a constant direction

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Johannes Kepler

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invented log books that he used as a tool for calculating planetary positions (1571-1630)

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Isaac Newton

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a genius, English scientist who invented calculus, developed theories of gravity and correctly organized the solar system (1643-1727)

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Kepler's Three Laws of Planetary Motion

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1. Each planet moves about the Sun in an orbit that is an ellipse, with the Sun at one focus of the ellipse. 2. The straight line joining a planet and the Sun sweeps out equal areas in space in equal intervals of time. 3. The squares of the planets' periods of revolution are in direction proportional to the cubes of the semimajor axes of their orbits.

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orbit

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the (usually elliptical) path described by one celestial body in its revolution about another

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ellipse

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An oval shape, which may be elongated or nearly circular; the shape of the planets' orbits.

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perihelion

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point in orbit nearest to the sun

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aphelion

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point in orbit farthest from the sun

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astronomical unit

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a unit of length used for distances within the solar system, equal to the average distance between the Earth and the Sun (approximately 93 million miles or 150 million kilometers)

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period

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an amount of time

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mass

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the property of a body that causes it to have weight in a gravitational field

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speed

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distance traveled per unit time

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velocity

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the speed of an object in a particular direction

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momentum

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the product of a body's mass and its velocity

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acceleration

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(physics) a rate of change of velocity

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force

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that which can change the momentum of a body; numerically, the rate at which the body's momentum changes. That which causes masses to accelerate.

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Newton's Three Laws of Motion

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1. Inertia. 2. F=ma. 3. For every action there is an equal and opposite reaction.

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conservation of momentum

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the law that the total amount of angular momentum in a system remains the same (in the absence of any force not directed toward or away from the point or axis about which the angular momentum is referred)

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gravity

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the mutual attraction of material bodies or particles

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fundamental forces of nature

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basic forces known to exist in nature (gravity)

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escape velocity

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the velocity a body must achieve to break away from the gravity of another body and never return to it

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weight

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a measure of the force due to gravitational attraction

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"weightless"

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being without a support force, as in free fall (ie. in an elevator and the cord breaks)

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asteroid belt

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the region of the solar system between the orbits of Mars and Jupiter in which most asteroids are located. The main belt, where the orbits are generally the most stable, extends from 2.2 to 3.3 AU from the Sun

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asteroid

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a stony or metallic object orbiting the Sun that is smaller than a major planet but that shows no evidence of an atmosphere or of other types of activity associated with comets

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volume

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a measure of the total space occupied by a body

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density

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the ratio of the mass of an object to its volume

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angular momentum

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a measure of the momentum associated with motion about an axis or fixed point

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Newton's law of gravity

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any two objects are attracted by a gravitational force, the size depends on masses of the two objects and the distance between the two objects

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inverse square relation

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the force of gravity decreases as the inverse square of the distance separating the objects

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Newton's version of Kepler's Third Law

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P^2 x (M1+M2) = R^3

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angular diameter

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angle subtended by the diameter of an object

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solar eclipse

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the eclipse of the Sun by the Moon, caused by the passage of the moon in front of the Sun

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corona

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the outer atmosphere of the Sun

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comet

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a small body of icy and dusty matter that orbits the Sun

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terrestrial planets

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Mercury, Venus, Earth, and Mars; also any planet with mass roughly in the interval from 10 Earths to 1/10 Earth, which orbits another star

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jovian (or giant) planets

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Jupiter, Saturn, Uranus, and Neptune; or planets of roughly that mass and composition in other planetary systems

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differentiation

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the gravitational separation of materials of different density in layers in the interior of an object

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meteor

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a flash of light observed when a small piece of solid matter enters Earth's atmosphere and burns up

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"shooting star"

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a meteor

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meteorite

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a portion of a meteoroid that survives passage through Earth's atmosphere and strikes the ground

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meteoroid

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a particle or chunk of typically rocky or metallic material in space before any encounter with the Earth

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greenhouse effect

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a warming that results when the sun's light (solar radiation) is trapped by an atmosphere

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solar nebula

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the cloud of gas and dust from which the solar system formed

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planetesimals

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objects, from tens to hundreds of kilometers in diameter, that formed in the solar nebula as an intermediate step between tiny grains and the larger planetary objects we see today; the comets and some asteroids may be leftover planetesimals

Astronomy Midterm Exam 1 – Flashcards

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