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Astronomy 1-3

field of view the area visible in an image. usually given as the diameter of a region
scientific notation the system of recording very large or very small numbers by using powers of 10
solar system the sun and its planets, asteroids, comets, and so on
planet a nonluminous body in orbit around a star, large enough to be spherical and to have cleared its orbital zone of other objects
star a globe of gas held together by its own gravity and supported by the internal pressure of its hot gases, which generate energy by nuclear fusion
astronomical unit average distance from Earth to the sun; 1.5x10^8 kilometers (93 million miles)
light year (ly) unit of distance equal to the distance light travels in one year
galaxy a large system of stars, star clusters, gas, dust, and nebulae orbiting a common center of mass
milky way the hazy band of light that circles our sky, produced by the glow of our galaxy
milky way galaxy the spiral galaxy containing our sun, visible in the night sky as the milky way
spiral arms long spiral pattern of bright stars, star clusters, gas and dust. they extend across the disks of spiral galaxies
supercluster a cluster of galaxy clusters
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
asterism a named grouping of stars that is not one of the recognized constellations
magnitude scale the astronomical brightness scale. the larger the number, the fainter the star
apparent visual magnitude a measure of the brightness of a star as seen by human eyes on Earth
flux a measure of the flow of energy through a surface. usually applied to light
celestial sphere an imaginary sphere of very large radius surrounding Earth to which the planets, stars, sun, and moon seem to be attached
scientific model a concept that organizes thought about an aspect of nature without necessarily being literally true
precession the slow change in orientation of the Earth's axis of rotation. one cycle takes nearly 26,000 years
zenith the top of the sky above an observers head
north celestial pole located directly above Earth's north pole
south celestial pole located directly below Earth's south pole
celestial equator lies halfway between the celestial poles
north point and south point points on the horizon closest to the celestial poles
east point and west point lie halfway between the north and south points, where the celestial equator always touches the horizon
angular distance angle between two lines extending from your eye to the two objects
arc minutes 1/60th of a degree measurement
arc seconds 1/60th of an arc minute
angular diameter angular distance from one edge to the other
circumpolar constellations groups of stars that never rise or set
rotation motion around an axis passing through the rotating body
revolution orbital motion about a point located outside the orbiting body
ecliptic the apparent path of the sun around the sky
zodiac a band centered on the ecliptic and enciricling the sky
evening star any planet visible in the sky just after sunset
morning star any planet visible in the sky just before sunrise
vernal equinox point where the sun crosses the celestial equator going northward
summer solstice point where the sun is farthest north
autumnal equinox point where the sun crosses the celestial equator going southward
winter solstice point where the sun is farthest south
perihelion Earth's closest point to the sun
aphelion Earth's most distant point from the sun
sidereal period how long the moon takes to circle the sky once and return to the same position among the stars
27.32 days how long does it take for the moon to orbit the Earth
sydonic period a complete cycle of lunar phases
29.53 days how long is the moon's sydonic period
solar eclipse the event that occurs when the moon passes directly between Earth and the sun, blocking your view of the sun
umbra the region of a shadow that is totally shaded
penumbra the portion of a shadow that is only partially shaded
annular eclipse a solar eclipse in which the solar photosphere appears around the edge of the moon in a bright ring, or annulus. features of the solar atmosphere cannot be seen during this type of eclipse
lunar eclipse the darkening of the moon when it moves through Earth's shadow
Saros cycle an 18-year, 11 1/3-day period after which the pattern of lunar and solar eclipses repeats
first principles something that seems obviously true and needs no further examination
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 the center, such as the Copernican universe
uniform circular motion all motion in the heavens must be made up of combinations of circles turning at uniform rates
parallax the apparent motion of an object because of the motion of the observer
retrograde motion backward motion
epicycle small circle making loops around a larger circle
deferent the larger circle with loops rotating around
equant point from which the offset Earth seems to be moving at a constant rate
paradigm a commonly accepted set of scientific ideas and assumptions
ellipse a closed curve around two points called the foci, such that the total distance from one focus to the curve and back to the other focus remains constant
semi-major axis half of the longest diameter of an ellipse
eccentricity a number between 1 and 0 that describes the shape of an ellipse; the distance from one focus to the center of the ellipse divided by the semi-major axis
empirical description of a phenomenon without explaining why it occurs
hypothesis a conjecture, subject to further tests, that accounts for a set of facts
theory a system of assumptions and principles applicable to a wide range of phenomena that has been repeatedly verified
natural law a theory that has been so well confirmed that it is almost universally accepted as correct
mass a measure of the amount of matter making up an object
weight the force that gravity exerts on an object
inverse square relation a rule that the strength of an effect (such as gravity) decreases in proportion as the distance squared increases
spring tide ocean tide of large range that occurs at full and new moon
neap tide ocean tide of small range occurring at first- and third- quarter moons
circular velocity the velocity needed to stay in a circular orbit
geosynchronous satellite orbits eastward with the rotation of Earth and remains above a fixed spot - ideal for communications and weather satellites
center of mass the balance point of the gravitational system
closed orbits return the orbiting object to its starting point
escape velocity the velocity needed to leave a body
open orbit does not return the object to Earth
Created by: pace_sauce