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ASTR 125 Final
| question + term | answer + definition |
|---|---|
| What do astronomers use for calculations? | The metric system and scientific notation for very large or very small numbers. |
| How big is the moon? | One-fourth the diameter of the Earth |
| How much larger is the sun than Earth? | 109 times in diameter |
| What does the solar system include? | It includes the sun at the center, all of the planets that orbit around it (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune), and their moons. |
| astronomical unit (AU) | The average distance from the Earth to the Sun. Mars, for example, orbits 1.5 AU from the sun. |
| light-year (ly) | The distance light can travel in one year. The nearest star is 4.2 ly from the sun. |
| Milky Way | The hazy band of light that encircles the sky. It is the Milky Way Galaxy seen from inside. The sun is one of billions of stars that fit inside the Milky Way Galaxy. |
| Galaxies | Contain many billions of stars. Our galaxy is about 80,000 ly in diameter and contains over 100 billion stars. |
| Spiral Arms | Some galaxies have them (they're graceful and bright with stars), but some galaxies are plain clouds of stars. |
| What forms can galaxies take? | clusters, clouds, filaments, and walls-the largest structures in the universe. Our galaxy is just one of billions. |
| When did the universe begin? | about 14 billion years ago, often thought to have occurred in an event called the Big Bang, which filled the universe with hot gas. |
| How long after the Big Bang did galaxies begin to form? | The first galaxies began to form and stars began to shine 400 million years after the Big Bang. |
| How long ago was the solar system formed? | The sun and planets in our solar system formed about 4.6 billion years ago. |
| When did life begin on Earth? | Life began in Earth's oceans soon after Earth formed but did not emerge onto land until only 400 million years ago. Dinosaurs evolved not long ago and only went extinct 65 million years ago. |
| When did humans first appear on Earth? | Humanlike creatures developed on Earth only about 4 million years ago, and human civilizations developed only about 10,000 years ago. |
| Which method does science follow? | Science follows the scientific method, in which scientists expect statements to be supported by evidence compared with hypotheses. |
| How many constellations exist? | Astronomers divide the sky into 88 constellations. Although the constellations originated in Greek and Middle Eastern mythology, the names are Latin. |
| asterisms | Named groups of stars that are not constellations. |
| Where do the names of stars usually come from? | The names of stars usually come from ancient Arabic, though modern astronomers often refer to a star by its constellation and a Greek letter assigned according to its brightness within the constellation. |
| magnitude scale | What astronomers use to refer to the brightness of stars. |
| apparent visual magnitude (mv) | The magnitude you see when you look at a star in the sky. It only includes types of light visible to the human eye and does not take into account the star’s distance from Earth. |
| flux | a measure of light energy related to intensity. The magnitude of a star is related directly to the flux of light received on Earth and so to its intensity. |
| celestial sphere | a scientific model of the sky, to which the stars appear to be attached. Because Earth rotates eastward, the celestial sphere appears to rotate westward on its axis. |
| north, south celestial poles | the pivots on which the sky appears to rotate, and they define the four directions around the horizon: the north, south, east, and west points. The point directly overhead is the zenith, and the point on the sky directly underfoot is the nadir. |
| celestial equator | an imaginary line around the sky above Earth’s equator that divides the sky into northern and southern halves. |
| angular distances | What astronomers call distances “on” the sky as if the stars, sun, moon, and planets were equivalent to spots painted on a plaster ceiling. They are measured in degrees, arc minutes, and arc seconds. |
| angular diameter | The angular distance across an object |
| How much of the celestial sphere can you see? | What you see of the celestial sphere depends on your latitude. Much of the southern hemisphere of the sky is not visible from northern latitudes. To see that part of the sky, you would have to travel southward over Earth’s surface. |
| Circumpolar constellations | constellations close enough to a celestial pole that they do not rise or set. |
| latitude | The angular distance from the horizon to the north celestial pole always equals your latitude. |
| Precession | Precession is caused by the gravitational forces of the moon and sun acting on the equatorial bulge of the spinning Earth and causing its axis to sweep around in a conical motion like the motion of a top’s axis. |
| How does Earth's axis of rotation precess? | Earth’s axis of rotation precesses with a period of 26,000 years, and consequently the celestial poles and celestial equator move slowly against the background of the stars. |
| What produces the cycle of day and night? | The rotation of Earth on its axis produces the cycle of day and night. |
| What produces the cycle of the year? | the revolution of Earth around the sun produces the cycle of the year. |
| Because Earth orbits the sun, the sun appears to move eastward along the ____ through the constellations completing a circuit of the sky in a year. | ecliptic |
| How does the ecliptic affect the Sun's positioning? | Because the ecliptic is tipped 23.4° to the celestial equator, the sun spends half the year in the northern celestial hemisphere and half in the southern celestial hemisphere. |
| How does the sun affect summer? | In each hemisphere’s summer, the sun is above the horizon longer and shines more directly down on the ground. Both effects cause warmer weather in that hemisphere and leave Earth’s other hemisphere cooler. |
| How does the sun affect winter? | In each hemisphere’s winter, the sun is above the sky fewer hours than in summer and shines less directly, so the winter hemisphere has colder weather, and the opposite hemisphere has summer. |
| vernal equinox | The beginning of spring |
| summer solstice | The beginning of summer |
| autumnal equinox | The beginning of autumn |
| winter solstice | The beginning of winter |
| When is the Earth closer to the sun? Further from the sun? | Earth is slightly closer to the sun at perihelion in January and slightly farther away from the sun at aphelion in July. This has almost no effect on the seasons. |
| evening stars | Planets visible in the sky at sunset |
| morning stars | planets visible in the dawn sky |
| What are the bases for astrology? | The locations of the sun and planets along the zodiac are diagramed in a horoscope, which are the bases for the ancient pseudoscience known as astrology. |
| Milankovitch hypothesis | changes in the shape of Earth’s orbit, in its precession, and in its axial tilt can alter the planet’s heat balance and cause the cycle of ice ages. Evidence found in seafloor samples support the hypothesis, and it is widely accepted today. |
| How do scientists test their own ideas? | Scientists routinely test their own ideas by organizing theory and evidence into a scientific argument. |
| The moon orbits eastward around Earth ___ _ _____ and rotates on its axis so as to keep the same side facing Earth throughout the month. | once a month |
| Because you see the moon by ________ ________, its shape appears to change as it orbits Earth and sunlight illuminates different amounts of the side facing Earth. | reflected sunlight |
| When do the lunar phases wax? | The lunar phases wax from new moon to first quarter to full moon |
| When do the lunar phases wane? | The lunar phases wane from full moon to third quarter to new moon. |
| A complete cycle of lunar phases takes 29.53 days, which is known as the moon’s ______ ______ | synodic period |
| The ________ ______ of the moon—its orbital period with respect to the stars—is a bit over two days shorter than the synodic period. | sidereal period |
| If a full moon passes through Earth’s shadow, sunlight is cut off, and the moon darkens in a _____ _______. | lunar eclipse |
| If the moon fully enters the dark umbra of Earth’s shadow, the eclipse is a _____ _____ ________. | total lunar eclipse |
| If the moon only grazes the umbra, the eclipse is a _______ _____ _______. | partial lunar eclipse |
| If the moon enters the partial shadow of the penumbra but not the umbra, the eclipse is a _________ _____ _______. | penumbral lunar eclipse |
| During ________, the eclipsed moon looks copper-red because of sunlight refracted through Earth’s atmosphere. | totality |
| What is the angular diameter of the sun and moon | about 0.5 degrees |
| A _____ _______ occurs if a new moon passes between the sun and Earth and the moon’s shadow sweeps over Earth’s surface along the ____ __ ________. | solar eclipse, path of totality |
| Observers inside the path of totality see a _____ _____ _______. | total solar eclipse |
| Observers just outside the path of totality see a _______ _____ _______. | partial solar eclipse |
| When the moon is near _______, the closest point in its orbit, its angular diameter is large enough to cover the sun’s photosphere and produce a total eclipse. | perigee |
| If the moon is near ______, the farthest point in its orbit, it looks too small and can’t entirely cover the photosphere. A solar eclipse occurring then would be an _______ _______. | apogee, annular eclipse |
| During a total eclipse of the sun, the bright ___________ of the sun is covered, and the fainter ______, ____________, and ___________ become visible. | photosphere, corona, chromosphere, prominences |
| Sometimes at the beginning or end of the total phase of a total solar eclipse, a small piece of the sun’s photosphere can peek out through a valley at the edge of the moon and produce a _______ ____ ______. | diamond ring effect |
| What is the safest way to view a solar eclipse? | The safest way to observe the partial phases of a solar eclipse is by pinhole projection. |
| When is the safest way to view a solar eclipse? | Only during totality, when the photosphere is completely hidden, is it safe to look at the sun directly. |
| What is one of the differences between lunar eclipses and solar eclipses? | Solar eclipses must occur at new moon, and lunar eclipses must occur at full moon. |
| What is another difference between lunar eclipses and solar eclipses? | Most new moons cross north or south of the sun, and there are no solar eclipses in those months. Similarly, most full moons cross north or south of Earth’s shadow, and there are no lunar eclipses in those months. |
| The moon’s orbit crosses the ecliptic at two locations called _____, and eclipses can occur only when the sun is crossing a node. | nodes |
| _______________ is the study of the astronomy of ancient peoples. Many cultures around the world observed the sky and marked important alignments. | Archeoastronomy |
| What ancient astronomy is most well known? | Greek astronomy, because written documents have survived. |
| Classical philosophers accepted as a _____ _________ that Earth was the unmoving center of the universe. | first principle |
| philosophers such as Plato argued that, because the sphere was the most perfect geometrical form, the heavens must be made up of spheres in uniform rotation. This led to the belief in _______ _______ ______. | uniform circular motion |
| Many astronomers argued that Earth could not be moving because they could see no ________ in the positions of the stars. | parallax |
| Aristotle’s estimate for the size of Earth was only about one-third of its true size. ____________ used the well at Syene to measure the diameter of Earth and got an accurate estimate. | Eratosthenes |
| The __________ ________ became part of the teachings of the great philosopher Aristotle, who argued that the sun, moon, and stars were carried around Earth on rotating crystalline spheres. | geocentric universe |
| Hipparchus, who lived about two centuries after Aristotle, devised a model in which the sun, moon, and planets revolved in circles called __________ with Earth near but not precisely at their centers. | eccentrics |
| __________ ______, the occasional westward (backward) motion of the planets, was difficult for astronomers to explain. | Retrograde motion |
| About AD 140, Aristotle’s model was given mathematical form in Claudius Ptolemy’s book Almagest. Ptolemy preserved the principles of geocentrism and uniform circular motion, but he added _________, _________ , and ______. | epicycles, deferents, equants |
| Ptolemy’s epicycles could approximate retrograde motion, but the _________ _____ was not very accurate, and it had to be revised a number of times as centuries passed. | Ptolemaic model |
| Copernicus devised a ____________ ________. He preserved the principle of uniform circular motion, but he argued that Earth rotates on its axis and revolves around the sun once a year. | heliocentric universe |
| Copernicus's theory was controversial because it contradicted Church teaching. He published his theory in his book __ _____________ in 1543, the same year he died. | De Revolutionibus |
| A __________ is a specific statement about nature that needs further testing, but a ______ is usually a general description of some aspect of nature that has been tested. | hypothesis, theory |
| A _______ ___ is a fundamental principle in which scientists have great confidence. | natural law |
| What was one reason the Copernican model won converts? | One reason the Copernican model won converts was that it was more elegant. Venus and Mercury were treated the same as all the other planets, and the velocity of each planet was related to its distance from the sun. |
| The shift from the geocentric ________ to the heliocentric paradigm is an example of a scientific revolution. | paradigm |
| Whose observations were later used by Kepler? | Tycho Brahe |
| Kepler found that the planets follow ________ with the sun at one focus, that they move faster when near the sun and that a planet’s orbital period squared is proportional to the _________ ____, a, of its orbit cubed. | ellipses, semimajor axis |
| The ____________, e, of an orbit is a measure of its departure from a perfect circle. A circle is an ellipse with an eccentricity of zero. | eccentricity |
| Kepler’s final book, ___ __________ ______ (1627), combined heliocentrism with elliptical orbits and predicted the positions of the planets well. | The Rudolphine Tables |
| Galileo used the newly invented telescope to observe the heavens, and he helped undermine the Ptolemaic universe. His discoveries of the phases of Venus, the satellites of Jupiter now known as the ________ _____, + the mountains of Earth’s moon | Galilean moons |
| What do historians of science think of Galileo's trial? | Historians of science view Galileo’s trial as a conflict between two ways of knowing about nature, reasoning from first principles and depending on evidence. |
| The 99 years from the death of Copernicus to the death of Galileo marked the birth of ______ ______. From that time on, science depended on evidence to test theories and relied on the mathematical analytic methods first demonstrated by Kepler. | modern science |
| Light is the visible form of _______________ _________, an electric and magnetic disturbance that transports energy at the speed of light. | electromagnetic radiation |
| The electromagnetic ________ includes gamma rays, X-rays, ultraviolet radiation, visible light, infrared radiation, and radio waves. | spectrum |
| You can think of a particle of light, a ______, as a bundle of waves that sometimes acts as a particle and sometimes acts as a wave. | photon |
| The energy a photon carries depends on its __________. The wavelength of visible light, usually measured in __________ | wavelength, nanometers |
| (10−9 m) or _________ (10−10 m), ranges from 400 nm to 700 nm (4000 to 7000 Å). | angstroms |
| Radio and ________ _________ have longer wavelengths and carry less energy. X-ray, gamma- ray, and ___________ radiation have shorter wavelengths and more energy. | infrared radiation, ultraviolet |
| _________ is the number of waves that pass a stationary point in 1 second. Wavelength equals the speed of light divided by the frequency. | Frequency |
| Earth’s atmosphere is fully transparent in only two ___________ _______ —visible light and radio. | atmospheric windows |
| An atom consists of a ________ surrounded by a cloud of _________. | nucleus, electrons |
| The nucleus is made up of positively charged _______ and uncharged ________. | protons, neutrons |
| What do the number of protons in an atom determine? | The number of protons in an atom determines which element it is. |
| Atoms of the same element (that is, having the same number of protons) with different numbers of neutrons are called ________. | isotopes |
| A neutral atom is surrounded by a number of negatively charged electrons equal to the number of protons in the nucleus. An atom that has lost or gained an electron is said to be _______ and is called an ___. | ionized, ion |
| Two or more atoms joined together form a ________. | molecule |
| The electrons in an atom are attracted to the nucleus by the _______ _____. | Coulomb force |
| As described by _______ _________, the _______ ______ that holds electrons in an atom is limited to certain energies, and that means the electrons may occupy only certain _________ ______. | quantum mechanics, binding energy, permitted orbits |
| The size of an electron’s orbit depends on its energy, so the orbits can be thought of as ______ ______ with lowest possible energy level known as the ______ _____. | energy levels, ground state |
| An _______ is one in which an electron is raised to a higher orbit by a collision between atoms or the absorption of a photon of the proper energy. | excited |
| Astronomical telescopes use a _______ ____ or ______ to gather light and focus it into a small image, which can be magnified by an _________. | primary lens, mirror, eyepiece |
| Short _____-______ lenses and mirrors must be more strongly curved and are more expensive to grind to shape. | focal-length |
| A __________ _________ uses a lens to bend the light and focus it into an image. Because of _________ __________, refracting telescopes cannot bring all colors to the same focus, resulting in color fringes around the images. | refracting telescope, chromatic aberration |
| An _________ ____ partially corrects the errors seen in refracting telescopes, but they're expensive and can't be made larger than 1m in diameter. | achromatic lens |
| __________ _________ use a mirror to focus the light and are less expensive than refracting telescopes of the same diameter. They also do not suffer from chromatic aberration. | Reflecting telescopes |
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