astronomy chapter 1-3 test – Flashcards
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field of view
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the area visible in an image, usually given as the diameter of the region.
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scientific notation
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the system of recording very large or very small numbers by using powers of 10.
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solar system
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the sun and its planets, asteroids, comets, and so on.
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planet
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a nonluminous body in orbit around a star, large enough to be spherical and to have cleared its orbital zone of other objects.
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star
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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.
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astronomical unit
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average distance from earth to the sun.
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light year
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unit of distance equal to the distance light travels in 1 year.
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galaxy
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a large system of stars, star clusters, gas, dust, and nebulae orbiting a common center of mass.
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milky way
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the hazy band of light that circles our sky, produced by the glow of our galaxy.
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milky way galaxy
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the spiral galaxy containing our sun, visible in the night sky as the milky way.
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spiral arms
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long spiral pattern of bright stars, star clusters, gas, and dust, these spiral arms extend across the disks of spiral galaxies.
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supercluster
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a cluster of galaxy clusters.
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constellation
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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.
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asterism
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a named grouping of stars that is not one of the recognized constellations.
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magnitude scale
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the astronomical brightness scale, the larger the number the fainter the star.
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apparent visual magnitude
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a measure of the brightness of a star as seen by human eyes on earth.
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flux
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a measure of the flow of energy through a surface, usually applied to light.
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celestial sphere
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an imaginary sphere of very large radius surrounding earth to which the planets, stars, sun, and moon seem to be attached.
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scientific model
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a scientific metaphor, a concept that organizes thought about an aspect of nature without necessarily being literally true.
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precession
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the slow change in orientation of the earths axis of rotation, one cycle takes nearly 26,000 years.
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rotation
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motion around an axis passing through the rotating body.
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revolution
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orbital motion about a point located outside the orbiting body.
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ecliptic
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the apparent path of the sun around the sky.
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zodiac
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a band centered on the ecliptic and encircling the sky, and the 12 constellations the sun goes through over a year.
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evening star
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any planet visible in the sky just after sunset.
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morning star
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any planet visible in the sky just before sunrise.
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solar eclipse
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the event that occurs when the moon passes directly between earth and the sun, blocking your view of the sun.
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umbra
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the region of a shadow that is totally shaded.
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penumbra
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the portion of a shadow that is only partially shaded.
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annular eclipse
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a solar eclipse in which the solar photosphere appears around the edge of the moon in a bright ring, or annulus and features of the solar atmosphere cannot be seen during an annular eclipse.
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lunar eclipse
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the darkening of the moon when it moves through earth's shadow.
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saros cycle
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an 18 year 11 1/3 day period after which the pattern of lunar and solar eclipses repeats.
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first principle
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something that seems obviously true and needs no further examination.
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geocentric universe
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a model universe with earth at the center, such as the Ptolemaic universe.
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heliocentric universe
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a model of the universe with the sun at the center, such as the Copernican universe.
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paradigm
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a commonly accepted set of scientific ideas and assumptions.
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ellipse
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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.
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semi-major axis, a
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half of the longest diameter of an ellipse.
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eccentricity, e
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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.
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empirical
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description of a phenomenon without explaining why it occurs.
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hypothesis
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a conjecture, subject to further tests that accounts for a set of facts.
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theory
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a system of assumptions and principles applicable to a wide range of phenomena that has been repeatedly verified.
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natural law
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a theory that has been so well confirmed that it is almost universally accepted as correct.
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mass
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a measure of the amount of matter making up an object.
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weight
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the force that gravity exerts on an object.
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inverse square relation
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a rule that the strength of an effect such as gravity decreases in proportion as the distance squared increases.
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spring tide
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ocean tide of large range that occurs at full and new moon, and note that the term spring refers to leaping, not to the season of spring.
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neap tide
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ocean tide of small range occurring at first and third quarter moon.
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equinox
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midpoint between summer and winter, equal day and night.
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solstice
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extreme of the seasons, winter solstice=shortest day, summer solstice=longest day.
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nut
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the goddess of the sky.
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Giordano Bruno
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said sun was a star and universe contained infinite number of worlds, he was burned at stake for heresy.
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Tycho Brahe
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had false nose from a duel, developed methods of observing sky before the telescope, and discovered tycho supernova.
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Copernicus
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believed sun was center of universe and earth rotated on axis and revolved around sun.
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Ptolemy
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made mathematical description of motions of planets, his model is called the "earth centered" or "geo-centric" model.
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retrograde motion
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earth moves faster along its orbit than the planets that lie farther from sun.
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proxima centauri
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closest star to the sun.
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December 21 winter solstice
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lowest point that the sun will be in the sky at noon.
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June 21 summer solstice
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solstice is at the highest point at the zenith.
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size of the universe order:
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earth, solar system, solar interstellar neighborhood, milky way galaxy, local galactic group, Virgo supercluster, local super clusters, observable universe.
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order of the planets closest to the sun:
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mercury, Venus, earth, mars, Jupiter, Saturn, Uranus, Neptune, Pluto.
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latitude
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parallel lines running east and west.
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longitude
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great circles running north and south.
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zenith
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point directly above your head.
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nadir
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point directly below.
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horizon
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circle of ground around you.
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meridian
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line from the north to the south.
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altitude
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angle of a star above your horizon.
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azimuth
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angle of star NE from north-360 degrees all around.
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celestial equator
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imaginary line in the sky representing the projection of the north and south pole on the night sky.
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right ascension
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the angle of the star with respect to the longitude.
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declination
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angle of the star with respect to the latitude.
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arc min. and arc sec.
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expresses angles in units in degrees.
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circumpolar constellations
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never set cause they are near a celestial pole.
