Astronomy — page 2 of 3

Astronomy terms

101. Initial Conditions The nature of a system's state when time equals zero.
102. Intensity With regards to light, intensity is the energy moving through a region of area per unit of time.
103. Intrinsic Luminosity A measure of the true brightness of an object. It is the amount of energy radiated into space every second by a celestial object, such as a star.
104. Inverse Square 1 divided by a quantity squared. 1/(r^2). The force due to gravity is proportional to 1 over distance squared. F~1/(d2).
105. Ion An atom or molecule that has lost or gained one or more electrons and has become electrically charged as a result.
106. Ion, Ionize An ion is an atom which has lost or gained one or more electrons so that it has a net electrical charge.
107. Ionization A process that produces ions, typically collisions between atoms or electrons, or by interaction with electromagnetic radiation.
108. Ionized The state in which an atom is missing on or more of its electrons, and is therefore positively charged.
109. Ionosphere The region of Earth's atmosphere that extends from about 50 to 300 miles above the surface of the planet and is made up of multiple layers dominated by…
110. irradiation (ih-RAY-dee-AY-shun) The use of high-energy radiation from x-rays, gamma rays, neutrons, protons, and other sources to kill cancer cells and shrink tumors.
111. Isotopes atoms that have the same number of protons, but a different number of neutrons are isotopes of each other.
112. Isotropic the property of being independent of direction. Isotropic radiation has the same intensity regardless of the direction of measurement.
113. Kelvin One Kelvin degree is equivalent to one Celsius degree. The difference between the two temperature scales: All motion within an atom ceases at zero Kelvin…
114. Lambda, Λ The cosmological constant, which measures the energy density of the vacuum.
115. Large Scale Structure Galaxies, galaxy clusters, and galaxy superclusters.
116. Last Scattering Surface The farthest back in the history of the universe that photons could travel freely.
117. Light A pane of glass; a window, or a compartment of a window.
118. Light Year The distance light travels in a year: {Distance equals rate times time: 300,000,000 meters per second, times roughly 30 million seconds equals roughly} 9.
119. Local Group A small cluster of more than 30 galaxies "near" to our galaxy, including the Andromeda galaxy and the Magellanic Clouds.
120. Luminosity The total energy released by an object emitting light, (in our case, this will be a star) per unit time (usually per second).
121. Magnetic Field A field of force around the Sun and the planets, generated by electrical currents, in which a magnetic influence is felt by other currents.
122. Magnetic Field Lines A magnetic field has both a strength and a direction at each point in space. For example, at each point Earth, the magnetic field -- and thus a compass --…
123. Magnetic Loops Field lines illuminated by hot plasma flowing along the magnetic field lines.
124. Magnetic Storms and Substorms A series of terrestrial disturbances – namely, the precipitation of auroras and rapid changes in Earth's magnetic field – caused by high-speed blasts…
125. Magnetism A force generated by electrical currents and changing electric fields. Magnetism is responsible for almost every feature in the solar atmosphere, from…
126. Magnetogram A magnetogram is an image of the Sun's magnetic flux. They are derived by using emission lines which are magnetically sensitive, which allows the magnetic…
127. Magnetosphere An area around a planet in which the planet’s magnetic field is stronger than the magnetic field carried by the solar wind.
128. Magnetotail The long magnetic tail of a magnetosphere drawn out by the flow of the solar wind.
129. Main Sequence Star A star that lies along a continuous band, known as the main sequence, extending from the upper left (hot, bright stars) to the lower right (cool, dim…
130. Mass Defect When two subatomic particles are bound together, their bound mass is slightly different than their mass if each particle is measured separately.
131. Matter-Dominated Universe When the density of matter is greater than that of any other component.
132. Maunder Minimum From 1645 to 1715, scientists believe there was a decrease in the total energy output from the Sun, as indicated by little or no sunspot activity.
133. Meson A kind of matter made from an even number of quark-antiquark constituents. The basic structure of most mesons is one quark and one antiquark.
134. Metastable Energy Density A theorized transient energy, often preceding a phase transition.
135. Mid-Class Explorer (MIDEX) (MIDEX) NASA's Mid-Class Explorer.
136. Milky Way The galaxy in which the Earth is found. When viewed from the Earth and its environs, it appears in the night sky as a hazy band of white light (hence…
137. model See Exhibit.
138. Muon The second heaviest charged lepton (with electron and tau), with electric charge -1.
139. Neutrino A lepton with no electric charge. Neutrinos participate only in weak and gravitational interactions and are therefore very difficult to detect.
140. Neutron A baryon with electric charge zero; it has the basic structure of two down quarks and one up quark (held together by gluons).
141. Nought Usually referring to the first value in a range, and denoted by a subscript, "0".
142. Nucleon Proton or neutron, part of atomic nucleus.
143. Nucleosynthesis The process by which atoms are formed by the coming together of subatomic particles and other smaller atoms.
144. Nucleus/Nuclei (plural- nuclei; adjective- nuclear ) The center of an atom. Nearly 100% percent of the mass of an atom is contained in the nucleus.
145. Observed Brightness The flux due to a light emitting object measured at the observer (in most cases, at the earth or a satellite).
146. Omega, Ω The ratio of the average total density of matter to the critical density required to make the universe flat and eventually stop its expansion.
147. Opaque to Radiation A condition when radiation is absorbed or scattered many times. For the first 400,000 years the universe was so hot that the matter was ionized and…
148. Open Universe , Ω A universe where the geometry of space is curved like an infinite saddle-shaped surface.
149. Parallax A method of finding astronomical distances. One uses a super distant background of stars as a reference plane, and observes the difference in position of…
150. Parsec A unit of distance, derived from a technique of finding distances to astronomical objects, called parallax. 3.1 x 1013 km or 3.26 light years.
151. Particle Accelerators A machine used to accelerate particles to high speeds, and thus, high energy compared to their rest-mass energy.
152. Particle Physics The study of fundamental particles (such as quarks and leptons) and the fundamental interactions (four forces).
153. Period Usually designated by T. This is the time interval of one complete oscillation of any wave. See Wavelength.
154. Phase Transition Change from one state of energy to another.
155. Photon A photon is both a wave and a particle. A beam of light is composed of these particles.
156. Photosphere The Sun’s surface, from which the light we actually see (with the human eye) is emitted. Temperatures average 5,800 K (9,900°F).
157. Planck Time The period of time immediately after the creation of the universe (10-43 s) during which quantum gravity is the principal phenomenon governing the…
158. Plasma (PLAZ-muh) The clear, yellowish, fluid part of the blood that carries the blood cells. The proteins that form blood clots are in plasma.
159. Positron The antiparticle of the electron, carry a charge that is opposite to an electron.
160. Primordial Nucleosynthesis Building of the atomic elements in the early universe when nuclei fused with one another. Most of the helium in the universe was created by this process.
161. Prominence A structure in the corona consisting of cool plasma supported by magnetic fields.
162. Prominences A structure in the Sun’s corona consisting of cool plasma supported by magnetic fields.
163. Proton A small, positively charged particle of matter found in the atoms of all elements.
164. Quantum Fluctuations Tiny changes in the energy of the vacuum.
165. Quantum Mechanics A theory of physics that is applicable to systems of extremely small scales (ie. the size of an atom). QM quantifies the "fuzzyness" of the universe.
166. Quark A fundamental matter particle that has strong interactions. Quarks have electric charge of either +2/3 (up, charm, top) or -1/3 (down, strange, bottom) in…
167. Quasar Short for Quasi-stellar Radio Source. A quasar behaves like a small galaxy powered by a super massive black hole, most of the time.
168. Radiation (RAY-dee-AY-shun) Energy released in the form of particle or electromagnetic waves.
169. Radiation Belt Magnetized planets, like Earth, are encircled by zones of particle radiation known as the "Van Allen belts," in which high-energy charged particles spiral…
170. Radiation Gas A mixture of photons and fast-moving charged particles.
171. Radiation-Dominated Universe When the density of radiation is greater than that of any other component.
172. Radiative Zone A layer of the Sun lying between the core and convection zone where en­ergy travels outward through the slow radiation, absorption, and re-radiation of…
173. Radio Waves Electromagnetic radiation with a wavelength greater than 1 mm (beyond infrared).
174. Recede To move away from the observer, which is, in most cosmological instances, the earth.
175. Redshift A change in the frequency or wavelength of light. This can arise from motion of the source (Doppler shift), expansion of space, or strong gravitational…
176. Relative Brightness How bright one object is compared to another. If they have the same intrinsic brightness then the relative brightness tells us the ratio of distances to…
177. Relativity Galileo first developed the principle of relativity, being the postulate that the laws of physics should take the same form for all observers in uniform…
178. Relic Some thing left over from a previous time period. Remnant products or evidence of early physical eras.
179. Scalar A constant number. 1, -16, .3534, 7346 are all scalars.
180. Scatter When refering to photons and light, scattering describes the phenomenon of a source absorbing, and then emanating light in all directions.
181. Sensitivity When referring to a medical test, sensitivity refers to the percentage of people who test positive for a specific disease among a group of people who have…
182. Simultaneous Occurring at the same time.
183. Solar Cycle An approximately 11-year pattern in the number of sunspots, coronal mass ejections (CMEs), solar flares, and other solar activity.
184. Solar Eclipse The passing of the Moon between the Sun and Earth. In a total solar eclipse, the Moon blocks all light from the solar disk, allowing us to see the solar…
185. Solar Flare An explosive release of electromagnetic radiation and huge quantities of charged particles from a small area of the solar surface.
186. Solar Maximum The month(s) during the 11-year solar cycle when the number of Sunspots reaches a maximum.
187. Solar Minimum The month(s) during the 11-year solar cycle when the number of Sunspots is lowest.
188. Solar Spectral Irradiance (SSI) (SSI) The amount of radiant energy of a particular wavelength that falls on a surface in a given amount of time.
189. Solar System The Sun and the family of objects that orbit it. The Solar System includes things like planets, moons, comets and asteroids, and a mysterious form of…
190. Solar Ultraviolet Irradiance The amount of energy released from the Sun in the ultraviolet portion of the spectrum at wavelengths shorter than 400 nm.
191. Solar Wind A stream of plasma coming out of the Sun in all directions at very high speeds—an average of about 400 km/sec, or a million mph.
192. Space Weather Refers to conditions on the Sun, in the solar wind, and in Earth’s space (magnetic field, ionosphere, and thermosphere) that can influence space- and…
193. Spacetime The theory of relativity says that time cannot be treated absolutely separately from space, only in one observer's relative view.
194. Spectra A range of different measurements. In terms of physics, spectra usually refers to the different wavelengths, or colors (if in the visible range) of light…
195. Spectral Line An emission (bright) or absorption (dark) of light at a specific frequency or wavelength.
196. Spectrograph A device that separates light by wavelength (color) in order to produce a spectrum that allows for the identification of elements within the light source.
197. Spectrum Electromagnetic radiation arranged in order of wavelength from Ion wavelength radio waves to short wavelength gamma rays.
198. Standard Candle A celestial object whose intrinsic brightness is known or can be estimated by some physical principle.
199. Static Unchanging over a length of time.
200. Steady State Theory A cosmological model where matter is created constantly as the universe expands so it remains homogenous and isotropic.