AST 101 Introduction to Astronomy Exam 1

field of view

the area visible in an image; usually given as the diameter of the region

scientific notation

the system of recording very large or very small by using powers of 10

Solar System

the Sun and the nonluminous objects that orbit it, including the planets, comets, and asteroids

planet

a nonluminous object, larger than a comet or asteroid, that orbits a star

star

a celestial object composed of gas held together by its own gravity and supported by nuclear fusion occurring in its interior

astronomical unit (AU)

average distance from Earth to the Sun; 1.5e8 km, or 93e6 miles

dwarf planet

an object that orbits the Sun and has pulled itself into a spherical shape but has not cleared its orbital lane of other objects. Pluto is one.

light-year (ly)

the distance light travels in one year

extrasolar planets

a planet orbiting a star other than the Sun

galaxy

a very large collection of gas, dust, and stars orbiting a common center of mass

Milky Way

the hazy band of light that circles the sky, produced by the combined light of billions of stars in our Milky Way galaxy

Milky Way Galaxy

the spiral galaxy containing the Sun; visible at night as the Milky Way

spiral arms

long, spiral patterns of bright stars, star clusters, gas, and dust that extends from the center to the edge of the disk of spiral galaxies

scientific method

the reasoning style by which scientists test theories against evidence to understand how nature works

constellations

one of the stellar patterns identified by name, usually of mythological gods, people, animals, or objects; also, the region of the sky containing that star pattern

International Astronomical Union (IAU)

an international society of astronomers that, among other activities, decides definitions and naming conventions for celestial objects and surface features. It defined the constellation boundaries in 1930 and reclassified Pluto as a dwarf planet in 2006.

asterisms

a named group of stars not identified as a constellation, for example, the Big Dipper

magnitude scale

the astronomical brightness scale; the larger the number, the fainter the star

apparent visual magnitudes (mv)

the brightness of a star as seen by human eyes on Earth

flux

a measure of the flow of energy onto or through a surface. Usually applied to light

scientific model

an intellectual concept designed to help you think about a natural process without necessarily being a conjecture of truth

celestial sphere

an imaginary sphere of very large radius surrounding Earth to which the planets, stars, Sun, and Moon seem to be attached

zenith

the point directly overhead on the sky

nadir

the point on the bottom of the sky directly under your feet

horizon

the line that marks the apparent intersection of the Earth and the sky

celestial equator

the imaginary line around the sky directly above Earth's equator

north celestial pole

the point on the celestial sphere directly above Earth's North Pole

south celestial pole

the point of the celestial sphere directly above Earth's South Pole

north point

the point on the horizon directly below the north celestial pole; exactly north

south point

the point on the horizon directly above the south celestial pole

east point

the point on the eastern horizon exactly halfway between the north point and the south point; exactly east

west point

the point on the western horizon exactly halfway between the north point and the south point; exactly west

angular distance

a measure of the separation between two objects in the sky; numerically equal to the angle in degrees between two lines extending from the observer's eye to the two objects

arc minutes

an angular measure; each degree is divided into 60 of these

arc seconds

an angular measure; each arc minute is divided into 60 of these

angular diameter

a measure of the size of an object in the sky; numerically equal to the angle in degrees between two lines extending from the observer's eye to opposite edges on the object

circumpolar constellations

any of the constellations so close to the celestial pole that they never set (or never rise) as seen from a given latitude

precession

the slow change in the direction of Earth's axis of rotation; one cycle takes nearly 26,000 years

rotation

the turning of a body about an axis that passes through its volume

revolution

the motion of an object in a closed path around a point outside its volume

ecliptic

the apparent path of the Sun around the sky

vernal equinox

the place on the celestial sphere where the Sun crosses the celestial equator moving northward; also the time of year when the Sun crosses this point, about March 21, and spring begins in the Northern Hemisphere

summer solstice

the point on the celestial sphere where the Sun is at its most northerly point; also, the time when the Sun passes this point, about June 22, and summer begins in the Northern Hemisphere

autumnal equinox

the point on the celestial sphere where the Sun crosses the celestial equator going southward. Also, the time when the Sun reaches this point and autumn begins in the Northern Hemisphere- around September 22.

winter solstice

the point on the celestial where the Sun is farthest south; also, the time of year when the Sun passes this point, about December 22, and winter begins in the Northern Hemisphere

perihelion

the orbital point of closest approach to the Sun

aphelion

the orbital point of greatest distance from the Sun

evening star

any planet visible in the sky just after sunset

morning star

any planet visible in the sky just before sunrise

zodiac

the band around the sky centered on the ecliptic within which the planets move

horoscope

a chart showing the positions of the Sun, Moon, planets, and constellations at the time of a person's birth; used in astrology to attempt to read character or foretell the future

Milankovitch hypothesis

the hypothesis that small changes in Earth's orbital and rotational motions cause the ice ages

scientific argument

an honest, logical discussion of observations and theories intended to reach a valid conclusion

lunar phase

the appearance of the Moon from Earth in terms of which portion is lit by the Sun versus which portion is dark, which changes in a regular monthly cycle

sidereal period

the period of rotation or revolution of an astronomical body relative to the stars

synodic period

the period of rotation or revolution of a celestial body with respect to the Sun

lunar eclipse

the darkening of the Moon when it moves through Earth's shadow

umbra

the region of a shadow that is totally shaded

penumbra

the portion of a shadow that is only partially shaded

total lunar eclipse

a lunar eclipse in which the Moon completely enters Earth's dark shadow

totality

the period during a solar eclipse when the Sun's photosphere is completely hidden by the Moon, or the period during a lunar eclipse when the Moon is completely inside the umbra of Earth's shadow

partial lunar eclipse

a lunar eclipse in which the Moon does not completely enter Earth's shadow

penumbral lunar eclipse

a lunar eclipse inn which the Moon enters the penumbra of Earth's shadow but does not reach the umbra

solar eclipse

the event that occurs when the Moon passes directly between Earth and Sun, blocking your view of the Sun

total solar eclipse

a solar eclipse in which the Moon completely covers the bright surface of the Sun

partial solar eclipse

a solar eclipse in which the Moon does not completely enter Earth's shadow

small-angle formula

the mathematical formula that relates an object's linear diameter and distance to its angular diameter

path of totality

the track of the Moon's umbral shadow over Earth's surface. The Sun is totally eclipsed as seen from within this path

apogee

the orbital point of greatest distance from Earth

perigee

the orbital point of closest approach to Earth

annular eclipse

a solar eclipse in which the solar photosphere appears around the edge of the Moon in a bright ring, or annulus. The corona, chromosphere, and prominences cannot be seen

photosphere

the bright visible surface of the Sun

corona

the faint outer atmosphere the Sun; composed of low-density, very hot, ionized gas

density

the amount of matter per unit volume in a material; measured in grams per cubic centimeter, for example

chromosphere

bright gases just above the photosphere of the Sun

promince

eruption on the solar surface; visible during total solar eclipses

diamond ring effect

a momentary phenomenon seen during some total solar eclipses when the ring of the corona and a bright spot of photosphere resemble a large diamond set in a silvery ring

node

a point where an object's orbit passes through the plane of Earth's orbit

eclipse season

that period when the Sun is near a node of the Moon's orbit and eclipses are possible

line of nodes

the line across an orbit connecting the nodes; commonly applied to the orbit of the Moon

eclipse year

the time the sun takes to circle the sky and return to a node of the Moon's orbit and eclipses are possible

Saros cycle

an 18 year 11 third day period after which the pattern of lunar and solar eclipses repeats

archaeostronomy

the study of the astronomy of ancient cultures

geocentric universe

a model Universe with Earth at the center, such as the Ptolemaic Universe

heliocentric universe

a model of the Universe with the Sun at its center, such as the Copernican Universe

uniform circular motion

the classical belief that the perfect heavens could move only by the combination of constant motion along circular orbits

first principle

an idea considered so obviously true that the idea does not need to be questioned. Classical philosophers accepted as this that Earth was the unmoving center of the Universe

eccentric

an off-center circular path

parallax

the apparent change in the position of an object a change in the location of the observer

retrograde motion

the apparent backward motion of planets as seen against the background of stars

deferent

in the Ptolemaic theory, the large circle around Earth along which the center of the epicycle moved

epicycle

the small circle followed by a planet in the Ptolemaic theory. The center of the epicycle follows a larger circle (deferent) around Earth

equant

the point off-center in the deferent from which the center of the epicycle appears to move uniformly

ellipse

a closed curve enclosing two points (foci) such that the total distance from one focus to any point on the curve back to the other focus equals a constant

semimajor axis, a

half of the longest axis of an ellipse

eccentricity, e

a measure of the flattening of an ellipse

empirical

description of a phenomenon without explaining why it occurs. I.e. Kepler's laws.

Galilean moons

the four largest satellites of Jupiter, named after their discover Galileo

natural motion

In Aristotelian physics, the motion of objects toward their natural places- fire and air upward and earth and water downward

violent motions

In Aristotelian physics, motion other than natural motion