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Astronomy DTU

Chapter 1 - 4

Angle the opening between two straight lines that meet at a point
Angular diameter (angular size) the arc angle across an object
Annular eclipse an eclipse of the Sun in which the Moon is too distant to cover the Sun completely so that a ring of sunlight is seen around the Moon at mideclipse
Arc angle the measurement of the angle between two objects or two parts of the same object
Asteroid (minor planet) any of the rocky objects larger than a few hundred meters in diameter (and not classified as a planet or moon) that orbits the Sun
Autumal equinox the intersection of the ecliptic and the celestial equator where the Sun crosses equator moving from north to south and the beginning of autumn (around September 23)
Black hole an object whose gravity is so strong that the escape velocity from it exceeds the speed of light
Celestial equator a great circle on the celestial sphere 90 degrees from the celestial poles
Celestial pole point about which the celestial sphere appears to rotate
Celestial Sphere a hypothetical sphere of very large radius centered on the observe; the apparent sphere of the night sky
Circumpolar stars all the stars that never set at a given latitude; all the stars between Polaris and the northern horizon
Comet A small body of ice and dust in orbit about the Sun. While passing near the Sun, a comet's vaporized ices give rise to a coma, tails, and a hydrogen envelope
Constellation any of the 88 contiguous regions that cover he entire celestial sphere, including all the objects in each region; also, a configuration of stars ofen named after an object, a person, or an animal
Declination the coordinate on the celestial sphere exactly analogous to latitude on Earth: measured north and south of the celestial equator
Degree a unit of angular measure or a temperature measure
Diurnal motion cyclic motion with a 1-day period
Eclipse path track of the tip of the Moon's shadow along the Earth's surface during a total or annular solar eclipse
Ecliptic annual path of the Sun on the celestial sphere; the plane of the Earth's orbit around the Sun
Equinox either of the two days of the two days of the year when the Sun crosses the celestial equator and is therefore directly over the Earth's equator
Gravitation tendency of all matter to attract all other matter
Line of nodes line along which the plane of the Moon's orbit intersects the plane of the ecliptic
Lunar eclipse eclipse during which the Earth blocks light that would have struck the Moon
Lunar phase names given to the apparent shapes of the Moon as see3n from Earth
Meteoroid small rock in interplanetary space
North celestial pole location on the celestial sphere directly above the Earth's northern rotation pole
Partial eclipse lunar or solar eclipse in which the eclipsed object does not appear completely covered
Penumbra portion of a shadow in which only part of the light source is covered by the shadow making body
Penumbral eclipse lunar eclipse in which the Moon passes only through the Earth's penumbra
Precession slow, conical motion of the Earth's axis of rotation caused by the gravitational pull of the Moon and Sun on the Earth's equatorial bulge
Precession of the equinoxes slow westward motion of the equinoxes along the ecliptic because of the Earth's precession
Revolution orbit of one body about another
Right ascension celestial coordinate analogous to longitude on Earth and measured around the celestial equator from the vernal equinox
Rotation spinning of a body about an axis passing through it
Scientific notation style of writing large and small numbers using powers of ten
Sidereal month period of the Moon's revolution about the Earth measured with respect to the Moon's location among the stars; 27 & 1/3 Earth days
Sidereal period orbital period of one object about another measured with respect to the stars
Solar corona Sun's outer atmosphere
Solar day From noontime to the next noontime; for Earth it is 24 hours
Solar eclipse eclipse during which the Moon blocks the Sun
South celestial pole location on the celestial sphere directly above the Earth's south rotation pole
Summer solstice point on the ecliptic where the Sun is farthest north of the celestial equator; the day with the largest number of daylight hours in the norther hemisphere
Synodic month (lunar month) period of revolution of the Moon with respect to the Sun; the length of one cycle of lunar phases; 29 and 1/2 Earth days
Terminator line dividing day and night on the surface of any body orbiting the Sun; the line of the sunset or sunrise
Time zone one of the 24 divisions of the Earth's surface separated by 15 degrees along lines of constant longitude ( with allowances for some political boundaries)
Total eclipse solar eclipse during which the Sun is completely hidden by the Moon, or a lunar eclipse during which the Moon is completely immersed in the Earth's umbra
Umbra central, completely dark portion of a shadow
Vernal equinox point on the ecliptic where the Sun crosses the celestial equator from south to north; the beginning of spring, around March 21
Winter solstice point on the ecliptic where the Sun is farthest south of the celestial equator; fewest hours of daylight in the northern hemisphere, around December 22
Zenith point on the celestial sphere directly overhead
Zodiac a band of 13 constellations around the sky through which the Sun appears to move throughout the year
Acceleration change in direction or magnitude of a velocity
Angular momentum measure of how much energy an object has stored in its rotation and/or revolution
Aphelion point in its orbit where a planet or other solar system body is farthest from the Sun
Astronomical unit average distance between the Earth and the Sun: 1.5 X 10 to the 8th power km = 93 million mi
Configuration (of a planet) particular geometric arrangement of the Earth, a planet, and the Sun
Conjunction alignment of two bodies in the solar system so that they appear in the same part of the sky as seen from Earth
Conservation of angular momentum law of physics stating that the total amount of angular momentum in an isolated system remains constant
Cosmology study of the formation, organization, and evolution of the universe
Direction motion gradual, eastward apparent motion of a planet against the background stars as seen from Earth
Ellipse closed curve obtained by cutting completely through a circular cone with a plane; the shape of planetary orbits
Elongation angle between a planet and the Sun as seen from Earth
Focus (of an ellipse) two points inside an ellipse, the sum of whose distances from any point on the ellipse is constant
Force which can change the momentum of an object
Galilean moons (satellites) any one of the four large moons of Jupiter (Callisto, Europa, Ganymede, Io) that is visible from Earth through a small telescope
Gravity (gravitation) tendency of all matter to attract all other matter
Heliocentric cosmology theory of the formation and evolution of the solar system with the Sun at the center
Hyperbola open curve obtained by cutting a cone with a plane
Inferior conjunction configuration when Mercury or Venus is directly between the Sun and the Earth
Kepler's laws 3 statements, formulated by Johannes Kepler, that describe the motions of the planets
Kinetic energy energy an object has as a result of its motion
Law of equal areas Kepler's 2nd law
Law of inertia (Newton's 1st law of motion) physical law that an object will stay at rest or move at a constant speed in a fixed direction unless acted upon by an outside force
Law of universal gravitation Newton's law of gravitation, which describes how the gravitational force between 2 bodies depends on their masses and separation
Light-year distance that light travels in a vacuum in 1 year
Mass measure of the total amount of material in an object
Model hypothesis that has withstood observational or experimental tests
Moment of inertia measure of the inertial resistance of an object to changes in the object's rotational motion about the axis
Momentum measure of the inertial resistance of an object to changes in the object's rotational motion about the axis
Newton's laws of motion Newton's equations that describe the motion of matter as a result of forces action on it
Occam's razor principle of choosing the simplest scientific theory that correctly explains any phenomenon
Opposition configuration of a planet when it is at an elongation of 180 degrees and thus appears opposite the Sun in the sky
Parabola open curve formed by cutting a circular cone at an angle parallel to the sides of the cone
Parallax apparent displacement of an object relative to more distant objects caused by fiewing it from different locations
Parsec unit of distance equal to 3.26 light-years
Perihelion point in its orbit where a planet is nearest the Sun
Potential energy energy stored in an object as a result of its location in space
Retrograde motion occasional backward (that is, westward) apparent motion of a planet against the background stars as seen from Earth, Retrograde motion is an optical illusion
Scientific method method of doing science based on observation, experimentation, and he formation of hypotheses (theories) that can be tested
Scientific theory idea about the natural world that is subject to verification and refinement
Semimajor axis (of an ellipse) half of the longest dimension of an ellipse
Sideral period orbital period of the one object about another measured with respect to the stars
Superior conjunction configuration when Mercury or Venus is on the opposite side of the Sun from Earth
Synodic period interval between successive occurrences of the same configuration of a planet as seen from Earth
Theory see scientific theory
Universal constant of gravitation constant of proportionality in Newton's law of gravitation, usually denoted G
Velocity quantity that specifies both direction and speed of an object
Weight force with which a body presses down on the surface of a world such as Earth
Work change in a object's energy as a result of a force being applied to it
Active optics system that adjusts a reflecting telescope in response to changes in temperature and shape of the mount; it helps optimize an image
Adaptive optics primary telescope mirrors that are continuously and automatically adjusted to compensate for the distortion of starlight due to the motion of the Earth's atmosphere
Angular resolution (resolution) angular size of the smallest detail of an astronomical object has stored in its rotation and/or revolution
Cassegrain focus optical arrangement in a reflecting telescope in which light rays are reflected by a secondary mirror through a hole in the primary mirror
Charge-coupled device (CCD) type of solid-state silicon wafer designed to detect photons
Coude focus reflecting telescope in which a series of mirrors direct light to a remote focus away from the moving parts of the telescope
Electromagnetic spectrum entire array of electromagnetic radiation
Electromagnetic radiation radiation consisting of oscillating electric & magnetic fields, namely gamma rays, X rays, visible light, ultraviolet & infrared radiation, & radio waves
Eyepiece lens magnifying lens used to view the image produced at the focus of a telescope
Focal length distance from a lens or concave mirror to where converging light rays meet
Focal plane plane at the focal length of a lens or concave mirror on which an extended object is focused
Focal point aka focus - place at the focal length where light rays from a point object (that is, one that is too distant or tiny to resolve) are converged by a lends or concave mirror
Frequency number of peaks or troughs of a wave that pass a fixed point each second and number also, number of complete vibrations or oscillations per second
Gamma ray most energetic form of electromagnetic radiation
Infrared radiation electromagnetic radiation of a wavelength longer than visible light but shorter than radio waves
Interferometry method of increasing resolving power by combining electromagnetic radiation obtained by 2 or more telescopes
Light-gathering power measure of how much light a telescope intercepts & brings to a focus
Magnification (magnifying power) number of times larger in angular diameter an object appears through a telescope than when it is seen by the naked eye
Newtonian reflector optical arrangement in a reflecting telescope in which a small, flat mirror reflects converging light rays to a focus on 1 side of the telescope tube
Objective lens principal lens of a refracting telescope
Photon discrete unit of electromagnetic energy
Pixel contraction of the term "picture element"; usually refers to 1 square of a grid into which the light-sensitive component of a charge-coupled device is divided
Primary mirror large, concave, light-gathering mirror in a reflecting telescope, analogous to the objective lens on a refracting telescope
Prime focus point in a reflecting telescope where the primary mirror focuses light
Radio telescope telescope designed to detect radio waves
Radio wave long-wavelength electromagnetic radiation
Reflecting telescope (reflector) telescope in which the principal light-gathering component is a concave mirror
Reflection rebounding of light rays off a smooth surface
Refracting telescope (refractor) telescope in which the principal light-gathering component is a lens
Refraction bending of light rays when they pass from 1 transparent medium to another
Schmidt corrector plate specially shaped lens used with spherical mirrors that corrects for spherical aberration and provides an especially wide field of view
Secondary mirror relatively small mirror used in reflecting telescopes to guide the light out the side or bottom of the telescope
Seeing disk size that a star appears to have on a photographic or charge-coupled-device image as a result of the changing refraction of the starlight passing through the Earth's atmosphere
Spectrum (plural spectra) result of electromagnetic radiation passing through a prism or grating so that different wvelengths are separated
Spherical aberration optical property where by different portions of a spherical lens or spherical, concave mirror have slightly different focal lengths, thereby producing a fuzzy image
Twinkling apparent change in a star's brightness, position, or color due to the motion of gases in the Earth's atmosphere
Ultraviolet (UV) radiation electromagnetic radiation of wavelengths shorter than those of visible light but longer than those of X rays
Very-long-baseline interferometry (VLBI) method of connecting widely separated radio telescopes to make observations of very high resolution
Wavelength distance between 1 successive peaks in a wave
X ray electromagnetic radiation whose wavelength is between that of ultraviolet light and gamma rays
Absorption line dark line in a continuous spectrum created when photons of a certain energy are absorbed by atoms or molecules
Absorption line spectrum dark lines superimposed on a continuous spectrum
Atom smallest particle of an element that has the properties characterizing that element
Atomic number number of protons in the nucleus of an atom
Blackbody hypothetical perfect radiator that absorbs & reemits all radiation falling upon it
Blackbody curve curve obtained when the intensity of radiation from a blackbody at a particular temperature is plotted against wavelength
Blueshift shift of all spectral features toward shorter wavelengths; the Doppler shift of light from an approaching source
Continuous spectrum (continuum) spectrum of light over a range of wavelengths without any spectral lines
Diffraction grating optical device consisting of closely spaced lines ruled on a piece of glass that is used like a prism to disperse light into a spectrum
Doppler shift or Doppler effect change in wavelength or radiation due to relative motion between the source & the observer along the line of sight
Electromagnetic force interaction between charged particles, the 2nd of 4 fundamental forces in nature
Electron negatively charged subatomic particle usually found in orbit about the nucleus of an atom
Element substance that cannot be decomposed by chemical means into simpler substances. every atom of the same element contains the same number of protons
Emission line bright line of electromagnetic radiation
Emission line spectrum spectrum that contains only bright emission lines
Energy flux amount of energy emitted from each square meter of an object's surface per second
Excited state orbit of an electron with energy greater than the lowest energy orbit (or state) available to that election
Ground state lowest energy level of an atom
Ion atom that has become electrically charged due to the loss or addition of 1 or more electrons
Ionization process by which an atom loses or gains electrons
Isotope atoms that all have the same number of protons (atomic number) but different numbers of neutrons. Their nuclear properties often differ greatly
Kirchhoff's laws 3 statements formulated by Gustav Kirchhoff describing what physical conditions produce each type of spectra
Luminosity rate at which electromagnetic radiation is emitted from a star or other object
Molecule 1 or more atoms bonded together
Neutron nuclear particle with no electric charge & with a mass nearly equal to that of the proton
Nucleus (of an atom) massive part of an atom, composed of protons & neutrons; electrons surround a nueleus
Periodic table listing of the chemical elements according to their properties; created by D. Mendeleev
Planck's law relationship between the energy carried by a photon & its wavelength
Proper motion change in the location of a star on the celestial sphere
Proton heavy, positively charged nuclear particle
Quantum mechanics branch of physics dealing with the structure & behavior of atoms & their interactions with each other & with light
Radial velocity portion of an object's velocity parallel to the line of sight
Radioactive zone region inside a star where energy is transported outward by the movement of photons through a gas from a hot location to a cooler 1
Redshift shifting to longer wavelengths of the light from remote galaxies & quasars; the Doppler shift of light from any receding source
Spectral analysis identification of chemicals by the appearance of their spectra
Spectrograph device for photographing a spectrum
Spectroscope device for directly viewing a spectrum
Stefan-Boltzmann law relationship stating that an object emits energy at a rate proportional to the 4th power of its temperature, in Kelvins
Strong nuclear force force that finds protons & neutrons together in nuclei
Transition (of an electron) change in energy & orbit of an electron around an atom or molecule
Transverse velocity portion of an object's velocity perpendicular to our line of sight to it
Weak nuclear force nuclear interaction involved in certain kinds of radioactivity decay
Wien's law relationship that the dominant wavelength of radiation emitted by a blackbody varies inversely with its temperature
Created by: 508204118