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| the study of the universe especially the objects in it |
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| The Sun and all the material that orbits it, including the planets, dwarf planets, and small solar system bodies. |
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| a large, glowing ball of gas that generates heat and light through nuclear fusion in its core. Example: Sun |
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An object that orbits a star and that, while much smaller than a star, is relatively large in size. May be rocky, icy, or gaseous in composition and they shine primarily by reflecting light from their star. Example: Earth.
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| An object that orbits a planet. The term satellite is also used more generally to refer to any object orbiting another object. |
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| A relatively small and rocky object that orbits a star. |
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| A relatively small and ice-rich object that orbits a star. |
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| The past, origin and future of the universe as a whole. |
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| A star (sometimes more than one star) and any planets and other materials that orbit it. |
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| A great island of stars in space, containing from a few hundred million to a trillion or more stars, all held together by gravity and orbiting a common center. |
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| The portion of the entire universe that can be seen from Earth, at least in principle. Only a tiny portion of the entire universe. |
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| The sum total of all matter and energy - that is, all galaxies and everything between them. |
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| A gigantic region of space where many individual galaxies and many groups and clusters of galaxies are packed more closely together than elsewhere in universe. |
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| The average distance between Earth and the Sun, which is about 150 million kilometers. More technically, 1 AU is the length of the semimajor axis of Earth's orbit. |
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| The distance that light can travel in 1 year, which is about 9.46 trillion kilometers. |
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| the spinning of an object around its axis, such as Earth's daily rotation around the axis. Example: Earth rotates once each day around its axis, which is an imaginary line connecting the North and South Poles. |
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| The orbital motion of one object around another due to gravity. Example: Earth orbits around the Sun once each year. |
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| EXPANSION (of the universe) |
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| The increase in the average distance between galaxies as time progresses. |
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| the name given to the event thought to mark the birth of the universe - scientists use the observed rate of expansion to calculate that it occurred about 14 billion years ago. |
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| STELLAR LIVES / NUCLEAR FUSION |
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| star is born when gravity compresses the material in a cloud until the center becomes dense/hot enough to generate energy by nuclear fusion, the process in which lightweight atomic nuclei smash together and stick (or fuse) to make heavier nuclei. The star "lives" as long as it can shine with energy from fusion, and "dies" when it exhausts its usable fuel. |
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| the explosion of a star. the returned matter mixes with other matter floating between the stars in the galaxy, eventually becoming part of new clouds of gas and dust from which new generations of stars can be born. |
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| recycles material expelled from dying stars in new generations of stars and planets. |
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| Early universe was composed of hydrogen, helium and a trace of lithium. Earth primarily composed of carbon, nitrogen, oxygen and iron which were manufactured by stars, some through nuclear fusion and others through nuclear reactions. |
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| WHAT IS OUR PLACE IN THE UNIVERSE? |
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| Earth is a planet orbiting the Sun. Our Sun is one of more than 100 billion stars in the Milky Way Galaxy. Our galaxy is one of about 40 galaxies in the Local Group. The Local Group is one small part of the Local Supercluster, which is one small part of the universe. |
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| On a 1-to-10 billion scale, the Sun is the size of a grapefruit, Earth is a ball point about 15 meters away, and the nearest stars are thousands of kilometers away. Our galaxy has so many stars that it would take thousands of years just to count them. |
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| the universe began in the Big Bang and has been expanding ever since, except in localized regions where gravity has caused matter to collapse into galaxies and stars. The Big Bang essentially produced only two chemical elements: hydrogen and helium. All other elements have been produced by stars and recycled within galaxies from one generation of stars to the next. |
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| HOW DO OUR LIFETIMES COMPARE TO THE AGE OF THE UNIVERSE? |
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| On a cosmic calendar that compresses the history of the universe into 1 year, human civilization is just a few seconds old, and a human lifetime lasts only a fraction of a second. |
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| Originally referred to objects that wandered among the constellations, but now applies to Earth and seven other objects in our solar system, while Pluto, Eris, and similar objects are classified as dwarf planets. |
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ideally the circle at eye level where the sky meets the ground. The four cardinal directions produce the north, south, east, and west points on the horizon.
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| the point directly overhead. |
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| the arc of a circle in the sky that contains the zenith and the north and south of the horizon. |
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| A region of the sky with well-defined borders |
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| The imaginary sphere on which objects in the sky appear to reside when observed from Earth. |
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| point directly over Earth's North pole. |
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| point directly over Earth's South pole. |
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| is a projection of Earth's equator into space, makes a complete circle around the celestial sphere. |
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| yearly path of the Sun around the celestial sphere. |
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| the constellations on the celestial sphere through which the ecliptic passes. |
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| the rotation of an object that always shows the same face to an object that is orbiting because its rotation period and orbital period are equal. |
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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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| occurs when Earth lies directly between the Sun and Moon, so Earth's shadow falls on the Moon. |
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| occurs when the Moon lies directly between the Sun and Earth, so the Moon's shadow falls on Earth. |
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| the plane of Earth's orbit around the Sun. |
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| the two points in the Moon's orbit where it crosses the ecliptic plane. |
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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 Sun. |
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| the dark central region of a shadow. |
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| The lighter, outlying regions of a shadow. |
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| a lunar eclipse in which the Moon becomes fully covered by Earth's umbral shadow. most spectacular; the Moon becomes dark and eerily red during totality when the Moon is entirely engulfed in the umbra, b/c Earth's atmosphere bends some of the red light from the Sun toward the Moon. |
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| a lunar eclipse during which the Moon becomes only partially covered by Earth's umbral shadows. |
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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. most common but they are the least visually impressive b.c the full moon darkens only slightly. |
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| A solar eclipse during which the Sun becomes fully blocked by the disk of the Moon. |
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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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| 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 of sunlight is still visible around the Moon's disk. |
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| APPARENT RETROGRADE MOTION |
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| the apparent motion of a planet, 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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| 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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| the tilt of Earth's axis causes the seasons. The axis points in the same direction throughout the year; therefore, as Earth orbits the Sun, sunlight hits different parts of Earth more directly at different times of year. |
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| WHY DO THE CONSTELLATIONS WE SEE DEPEND ON THE TIME OF YEAR? |
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| the visible constellations vary with the seasons because our night sky lies in different directions in space as we orbit the Sun. |
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| WHY DO WE SEE PHASES OF THE MOON? |
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| the phase of the Moon depends on its position relative to the Sun as it orbits Earth. the half of the Moon facing the Sun is always illuminated while the other half is dark, but from Earth we see varying combinations of the illuminated and dark faces. |
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| We see lunar eclipse when Earth's shadow falls on the Moon, and a solar eclipse when the Moon blocks our view of the Sun. We do not see an eclipse at every new and full moon because the Moon's orbit is slightly inclined to the ecliptic plane. Eclipses come in different types, depending on where the dark umbral and lighter penumbral shadows fall. |
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| WHY DID THE ANCIENT GREEKS REJECT THE REAL EXPLANATION FOR PLANETARY MOTION? |
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| planets generally move eastward relative to the stars from night to night, but sometimes they reverse course for weeks to months in what we call apparent retrograde motion. this motion is simply explained in a Sun-centered system, but the Greeks rejected this model in part because they could not detect stellar parallax - slight apparent shifts in stellar positions over the course of the year that must occur if Earth orbits the Sun. |
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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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any of the ancient Greek models that were used to predict planetary positions under the assumption that Earth lay in the center of the universe. Heavens must be "perfect"; objects moving on perfect spheres or in perfect circles.
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the geocentric model of the universe developed by Ptolemy in about 150 A.D. Sufficiently accurate to remain in use for 1500 years.
o Ptolemaic model of the superior planets:
o The size of the retrograde loop in the sky determines the size of the epicycle.
o The duration of retrograde motion determines the epicycle period
o The deferent periods come from the observer motion with respect to the stars
o The lines connecting the centers of the epicycles with their planets are parallel to the Earth-Sun line. This makes the retrograde motion occur at opposition.
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| PTOLEMAIC MODEL OF THE INFERIOR PLANETS |
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The centers of the epicycles of Mercury and Venus stay on the Earth – Sun line. This keeps them near the Sun in our sky. The maximum distance of Mercury and Venus from the Sun in the sky determine the sizes of their epicycles. The durations of their retrograde motions determine their periods on the epicycles.
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| PTOLEMAIC MODEL OF THE SUPERIOR PLANETS |
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The size of the retrograde loop in the sky determines the size of the epicycle. The duration of retrograde motion determines the epicycle perioD. The deferent periods come from the observer motion with respect to the stars. The lines connecting the centers of the epicycles with their planets are parallel to the Earth-Sun line. This makes the retrograde motion occur at opposition.
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| simple device for measuring the solar motion. consists of a vertical stick that casts a shadow. |
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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. includes: asteroid Ceres and the Kuiper belt (Pluto, Eris, Haumea, and Makemake). |
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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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law stating that the orbit of each planet about the Sun is an ellipse with the Sun at one focus.
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| the principle that, as a planet moves around its orbit, it sweeps out equal areas in equal times. This tells us that planet moves faster when it is closer to the Sun (near perihelion) than when it is farther from the Sun (near aphelion) in its orbit. |
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| a principle that the square of a planet's orbital period is proportional to the cube of its average distance from the Sun (semimajor axis), which tells us that more distant planets move more slowly in their orbits. |
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| NEWTON'S FIRST LAW OF MOTION |
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| principle that, in the absence of a net force, an object moves with constant velocity |
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| NEWTON'S SECOND LAW OF MOTION |
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law stating how a net force affects an object's motion. force = rate of change in momentum, or force = mass x acceleration.
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| NEWTON'S THIRD LAW OF MOTION |
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| principle that for any force, there is always an equal and opposite reaction force. |
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the distance between successive peaks or troughs
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The speed of a peak or trough. The speed of light (in a vacuum) is 300,000 km/s = 3.0 × 108 m/s. This speed is very large, sufficiently large that light travels instantaneously in everyday life (except for phone conversations going through communication satellites).
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| number of waves which pass a fixed point per second. usually expressed in Hertz. |
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| HOW DID THE GREEKS EXPLAIN PLANETARY MOTION? |
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| developed models in an attempt to explain their observations of nature. The Greek Earth-centered model reached its height with the model of Ptolemy. |
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| HOW DID THE COPERNICAN REVOLUTION CHANGE OUR VIEW OF THE UNIVERSE? |
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| replaced the ancient Earth-centered view of the universe with a new view in which Earth is just one planet going around the Sun. |
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| THREE HALLMARKS OF SCIENCE |
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1. modern science seeks explanation for observed phenomena that rely solely on natural causes.
2. science progresses through the creation and testing of models of nature that explain the observation as simply as possible.
3. a scientific model must make testable predictions about natural phenomena that would force us to revise or abandon the model if the predictions did not agree with observations. |
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| WHAT IS A SCIENTIFIC THEORY? |
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| simple yet powerful model that explains a wide variety of observations in terms of just a few general principles and has attained the status of a theory by surviving repeated and varied testing. |
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The diameter of the objective lens or mirror that collects light from the scene. The larger the diameter, the more light is collected.
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The distance from the objective lens or mirror to the image when the object is at infinity. The longer the focal length, the larger the image formed. One did have to give up something when compared to the pinhole, now an image can be formed only at a fixed distance from the aperture.
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