Astronomy Exam 1

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constellation

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a region of the sky with well-defined borders

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celestial sphere

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the imaginary sphere on which objects in the night sky appear to reside when observed from Earth

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north celestial pole (NCP)

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

- does not move on the celestial sphere over the course of the day

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south celestial pole (SCP)

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

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celestial equator

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the extension of Earth's equator onto the celestial sphere

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ecliptic

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the Sun's apparent annual path among the constellations

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local sky

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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)

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horizon

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a boundary that divides what we can see from what we cannot see

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zenith

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the point directly overhead, which has an altitude of 90 degrees

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meridian

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a half-circle extending from your horizon (altitude 0 degrees) due south, through your zenith, to your horizon, due north

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direction

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(in local sky) one of the two coordinates (the other is altitude) needed to pinpoint an object in the local sky. It is the direction you must face N, S, E, W, in which you must face to see the object

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altitude

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(above horizon) the angular distance between the horizon and an object in the sky

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angular size

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(or angular distance) a measure of the angle formed by extending imaginary lines outward from our eyes to span an object (or the space between two objects)

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angular distance

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(or angular size) a measure of the angle formed by extending imaginary lines outward from our eyes to span an object (or the space between two objects)

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arcminutes

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1/60 of one degree

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arcseconds

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1/60 of an arcminute or 1/3600 of one degree

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circumpolar

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a star that always remains above the horizon for a particular latitude

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latitude

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the angular north-south distance between Earth's equator and a location on Earth's surface

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longitude

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the angular east-west distance between the prime-meridian and a location on Earth's surface

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prime meridian

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the meridian of longitude that passes through Greenwich, England, define to be longitude 0 degrees

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zodiac

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the constellations on the celestial sphere through which the ecliptic passes

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summer solstice

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refers both to the point on the celestial sphere where the ecliptic is farthest north of the celestial equator and to the moment in time when the Sun appears at that point each year

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winter solstice

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refers both to the point on the celestial sphere where the ecliptic is farthest south of the celestial equator and to the moment in time when the Sun appears at that point each year

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vernal equinox

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refers both to the point in Pisces on the celestial sphere where the ecliptic is crosses the celestial equator and to the moment in time when the Sun appears at that point each year

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fall equinox

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refers both to the point in Virgo on the celestial sphere where the ecliptic is crosses the celestial equator and to the moment in time when the Sun appears at that point each year

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precession

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the gradual wobble of the axis of a rotating object around a vertical line

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lunar phases

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the state determined by the portion of the visible face of the Moon that is illuminated by sunlight

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synchronous rotation

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the rotation of an object that always shows the same face to an object that it is orbiting becuse its rotation period and orbital period are equal

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eclipse

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an event in which one astronomical object casts a shadow on another or crosses our line of sight to the other object

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lunar eclipse

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an event that occurs when the Moon passes through Earth's shadow, which can occur only at full moon. A lunar eclipse may be total, partial, or penumbral

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solar eclipse

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an event that occurs when the Moon's shadow falls on Earth, which can occur only at new moon. A solar eclipse may be total, partial, or annular

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nodes

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the two points in the Moon's orbit where it crosses the ecliptic plane

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umbra

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the dark central region of a shadow

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penumbra

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the lighter, outlying regions of a shadow

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total lunar eclipse

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a lunar eclipse in which the Moon becomes fully covered by Earth's umbral shadow

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partial lunar eclipse

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a lunar eclipse during which the Moon becomes only partially covered by Earth's umbral shadow

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penumbral eclipse

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a lunar eclipse during which the Moon passes only within Earth's penumbral shadow and does not fall within the umbra

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totality

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the portion of a total lunar eclipse during which the Moon is fully within Earth's umbral shadow or a total solar eclipse during which the Sun's disk is fully blocked by the Moon

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total solar eclipse

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a solar eclipse during which the Sun become fully blocked by the disk of the Moon

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annular eclipse

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a solar eclipse during which the Moon is directly in front of the Sun but its angular size is not large enough to fully block the Sun; thus, a ring (or annulus) of sunlight is still visible around the Moon's disk

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partial solar eclipse

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a solar eclipse during which the Sun becomes only partially blocked by the disk of the Moon

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eclipse seasons

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periods during which lunar and solar eclipses can occur because the nodes of the Moon's orbit are aligned with Earth and the Sun

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apparent retrograde motion

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the apparent motion of a plant, as viewed from Earth, during the period of a few weeks or months when it moves westward relative to the stars in our sky

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stellar parallax

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the apparent shift in the position of a nearby star (relative to distant objects) that occurs as we view the star from different positions in Earth's orbit of the Sun each year

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archaeoastronomy

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a combination of archaeology and astronomy (i.e. discovering ancient astronomical tools and devices)

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model

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a representation of some aspect of nature that can be used to explain and predict real phenomena without invoking myth, magic, or the supernatural

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geocentric model

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any of the ancient Greek models that were used to predict planetary position under the assumption that Earth lay in the center of the universe

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Ptolemaic model

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the geocentric model of the universe developed by astronomer Ptolemy in about 150 A.D.

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Copernican Revolution

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the dramatic change, initiated by Copernicus, that occurred when we learned that Earth is a planet orbiting the Sun rather than the center of the universe

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ellipse

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a type of oval that happens to be the shape of bound orbits.

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foci (focus)

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one of two special points within an ellipse tat lie along the major axis; when one object orbits a second object, the second object lies at one focus of the orbit

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semimajor axis

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half the distance across the long axis of an ellipse; usually referred to as the average distance of an orbiting object

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eccentricity

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a measure of how much an ellipse deviates from a perfect circle; defined as the center-to-focus distance divided by the length of the semimajor axis

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Kepler's 1st Law

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the orbit of each planet about the sun is an ellipse with the sun at one focus

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Kepler's 2nd Law

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as a planet moves around its orbit, it sweeps out equal areas in equal times; a planet moves faster when it is closer to the sun than when it is farther from the Sun in its orbit

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Kepler's 3rd Law

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the square of a planet's orbital period is proportional to the cube of its average distance from the Sun

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perihelion

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the point at which an object orbiting the Sun is closest to the Sun

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aphelion

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the point at which an object orbiting the Sun is farthest from the Sun

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hypothesis

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a tentative model proposed to explain some set of observed facts, but which has not yet been rigorously tested and confirmed

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pseudoscience

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something that purports to be science or may appear to be scientific but that does not adhere to the testing and verification requirements of the scientific method

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Occam's Razor

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often times the simplest answer is the most correct

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paradigm

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a general pattern of thought that tends to shape scientific study during a particular time period

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theory

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a model of some aspect of nature that has been rigorously tested and has passed all tests to date

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astrology

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the study of the movements and relative positions of celestial objects as a means for divining information about human affairs and terrestrial events.

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"hallmarks" of science

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- modern science seeks explanation for observed science that relies solely on natural causes

- creation and testing of models that explain in the simplest terms

- must make testable observations that allow us to revise or abandon the model if predictions don't agree with future observations

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solar system

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a star (sometimes more than one star) and all the objects that orbit it

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Milky Way Galaxy

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used both as the name of our galaxy and to refer to the band of light we see in the sky when we look into the planet of the plane of the Milky Way Galaxy

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galaxy

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a huge collection of anywhere from a few hundred million to more than a trillion stars, all bound together by gravity

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Local Group

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the group of about 40 galaxies to which the Milky Way Galaxy belongs

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galaxy clusters

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a collection of a few dozen or more galaxies bound together by gravity; smaller collections of galaxies are simply called groups

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superclusters

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the largest known structures in the universe, consisting of many clusters of galaxies, groups of galaxies, and individual galaxies

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universe

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the sum total of all matter and energy

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astronomical unit (AU)

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the average distance (semimajor axis) of Earth from the Sun, which is about 150 million km

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light-year (ly)

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the distance that light can travel in 1 year, which is 9.46 trillion km

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observable universe

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the portion of the entire universe that, at least in principle, can be seen from Earth

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star

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a large, glowing ball of gas that generates energy through nuclear fusion in its core. the term star is sometimes applied to objects that are in the process of becoming true stars (e.g. protostars) and to the remains of stars that have died (e.g. neutron stars)

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planet

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a moderately large object that orbits a star and shines primarily by reflecting light from its star. more precisely as of 2006, 1. orbits a star, 2. is massive enough for its own gravity to give it a nearly round shape, 3. has cleared the neighborhood around its orbit (objects that meet the first 2 are dwarf planets i.e. Pluto)

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dwarf planet

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an object that orbits the Sun and is massive enough for its gravity to have made it nearly round in shape, but that does not qualify as an official planet because it has not cleared its orbital neighborhood

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moon (satellite)

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an object that orbits a planet

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asteroid

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a relatively small and rocky object that orbits a star; officially considered a part of a category known as "small solar system bodies"

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comet

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a relatively small, icy object that orbits a star. like asteroids, comets are officially considered part of a category known as "small solar system bodies"

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nebula

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an interstellar cloud of gas a/o dust

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small solar system body

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an asteroid, comet, or other object that orbits a star but is too small to qualify as a planet or dwarf planet

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Big Bang

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the name given to the event thought to mark the birth of the universe

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nuclear fusion

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the process in which two (or more) smaller nuclei slam together and make one larger nucleus

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orbit

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the path followed by a celestial body because of gravity; an orbit may be bound (elliptical) or unbound (parabolic or hyperbolic

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ecliptic plane

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the plane of Earth's orbit around the Sun

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axis tilt

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the amount by which a planet's axis is tilted with respect to a line perpendicular to the ecliptic plane

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supernovae

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how the most massive stars die in titanic explosions

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sidereal day

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the time of 23 hours and 56 minutes 4.09 seconds between successive appearances of any particular star on the meridian; essentially, the true rotation period of Earth.

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solar day

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24 hours, which is the average time between appearances of the Sun on the meridian

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celestial coordinates

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the coordinates of right ascension and declination that fix an object's position on the celestial sphere

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declination (dec)

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- altitude of any star

- analogous to latitude, but on the celestial sphere; it is the angular north-south distance between the celestial equator and a location on the celestial sphere

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right ascension (RA)

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- tells us how long after the spring equinox the object crosses the meridian

- analogous to longitude, but on the celestial sphere; the angular east-west distance between the spring equinox and a location on the celestial sphere

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tropic of Cancer

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the circle on Earth with latitude 23.5 degrees north, which marks the northernmost latitude at which the Sun ever passes directly overhead (which it does at noon on the summer solstice)

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tropic of Capricorn

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the circle on Earth with latitude 23.5 degrees south, which marks the southernmost latitude at which the Sun ever passes directly overhead (which it does at noon on the winter solstice)

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Arctic Circle

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the circle on Earth with latitude 66.5 degrees north

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Antarctic Circle

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the circle on Earth with latitude 66.5 degrees south

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global positioning system (GPS)

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a system of navigation by satellites orbiting the Earth

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Most of the material that makes up Earth and all life on Earth, including humans, was formed

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inside stars that died before Earth formed

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distance to the nearest start to Sun is

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about 4 light-years

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The diameter of the Milky Way is about

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100,000 light-years

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If you could count all the starts in the Milky Way Galaxy at a rate of one star per second, it would take...

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about 3,000 years

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Your speed due to Earth's rotation is

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about 1,000 km/hour

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The Sun completes one revolution of the Milky Way galaxy every...

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230,000,000 years

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Earth's axis of rotation is tilted in respect to...

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the axis of its orbit around the Sun

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The ecliptic is

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- the path of the Sun on the celestial sphere

- the projection of Earth's orbit onto the celestial sphere

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Meridian

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the boundary between the eastern and western halves of your local sky

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What time does the first quarter moon rise?

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noon

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How does an annular solar eclipse occur?

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Earth passes behind the moon's umbra