Astronomy Vocabulary from the Textbook Compiled

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15 Apr 2012
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Astronomy Vocab
CHAPTER 1 OUR PLACE IN THE UNIVERSE
Solar System A star (sometimes more than one) and all the objects that orbit it
Milky Way Galaxy name of our galaxy and the band of light we see in the night sky
Galaxy - huge collection of a few hundred million to more than a trillion stars bound by gravity
Local Group the group of about 40 galaxies to which the Milky Way belongs
Galaxy Clusters collection of a few dozen or more galaxies bound together by gravity
Superclusters largest known structures in universe consisting of many galaxy clusters
Universe sum total of all matter and energy
Big Bang event thought to mark the birth of the universe
Nuclear Fusion process when two or more smaller nuclei slam together to make a larger one
Asteroid relatively small rocky object orbiting a star
Comet relatively small ice-rich object that orbits a star
Observable Universe portion of the entire universe that can be seen from Earth; probably only a tiny
part of theuniverse
Light-Year Distance light can travel in a year (9.46 trillion km)
Astronomical Unit (AU) average distance of Earth from sun (150 million km)
CHAPTER 3 THE SCIENCE OF ASTRONOMY
Ellipse type of oval that is the shape of a bound orbit
Focus one of two special points within an ellipse that lie along the major axis. When one object orbits
a second object the second object lies at one focus of the orbit
Semimajor Axis half the distance across the long axis of an ellipse
Eccentricity measure of how much an ellipse deviates from a perfect circle; centre-to-focus distance
divided by length of semimajor axis
Kepler’s Laws of Planetary Motion Three laws discovered by Kepler that describe the motion of the
planets around the sun
Kepler’s First Law orbit of each planet around the sun is an ellipse with the sun at a focus
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Kepler’s Second Law as a planet moves around its orbit, it sweeps out equal areas at equal times;
Planet moves faster at the sun (perihelion) and slower farther away (aphelion)
Kepler’s Third Law Square of a planet’s orbital period is proportional to the cube of its average
distance from the sun (semimajor axis); the more distant a planet the slower the orbit p² = a³
CHAPTER 4 MAKING SENSE OF THE UNIVERSE
Speed how far something goes in an amount of time
Velocity tells speed and direction of an object
Acceleration when velocity changes
Acceleration of Gravity acceleration of a falling object (9.8 m/s on Earth)
Momentum mass x velocity
Force anything that can change momentum
Net Force overall force to which an object responds; mass x acceleration
Angular Momentum momentum attributed to rotation; m x v x r (radius)
Torque twisting force that can change an object’s angular momentum
Mass amount of matter in something
Weight depends on mass and forces (like gravity)
Free-Fall condition in which an object is falling without resistance; weightless
Newton’s Laws of Motion three basic laws that describe an object’s reaction to force
Newton’s First Law in the absence of net force, an object moves at constant velocity
Newton’s Second Law how net force effects an object’s motion; force = mass x acceleration
Newton’s Third Law for every force there is an equal and opposite reaction force
Conservation of Momentum in absence of net force, total momentum remains constant
Conservation of Angular Momentum in absence of net torque, total angular momentum remains
constant
Conservation of Energy energy can be neither created or destroyed it can only change form
Mass-Energy energy contained in mass itself
Bound Orbit orbit on which an object travels repeatedly around another object; elliptical
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Unbound Orbit orbit on which object moves towards a large body only once; parabolic or hyperbolic
CHAPTER 5 LIGHT AND MATTER
Electromagnetic Spectrum complete spectrum of light including: radio, infrared, visible, ultraviolet, x-
rays and gamma rays
Emission the process by which matter emits energy in the form of light
Absorption the process by which matter absorbs radiative energy
Transmission the process in which light passes through matter without being absorbed
Reflection/Scattering the process by which matter changes the direction of light
Wavelength the distance between adjacent peaks (or troughs) of a wave
Frequency the rate at which peaks of a wave pass by a point, measured in units of 1/s often
Cycles per second units of frequency for a wave
Hertz same as cycles per second
Electromagnetic Wave a synonym for light which consists of waves of electric and magnetic fields
Speed of Light the speed at which light travels which is about 300,000 km/s
Visible Light the light which our eyes can see
Electromagnetic Radiation another name for light of all types
Infrared light with wavelengths that fall between radio waves and visible light
Radio Waves light with very long wavelengths and low frequencies longer than infrared
Microwaves light with wavelengths in the range of micrometres or millimetres; generally considered a
subset of radio waves
X-Rays light with wavelengths that fall in the portion of the electromagnetic spectrum between
ultraviolet and gamma rays
Gamma Rays light with very short wavelengths (shorter than X-Rays)
Atoms consist of a nucleus made from protons and neutrons, surrounded by a cloud of electrons
Protons particles found in atomic nuclei with positive electrical charge, built from three quarks
Neutrons particles with no electrical charge found in atomic nuclei, built from three quarks
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