Appendix B Acronyms and Abbreviations Units of Measure and some Physical Constants A............. ampere - unit of electric current [named after André M. Ampère (1775-1836), French physicist]. 1 A represents a flow of one coulomb of electricity per second (or: 1A = 1C/s) Ah............ ampere hour Å............. angstrom - unit of length (used in particular for the short wavelength spectrum); 1Å= 10-10 m [named after Anders Jonas Ängström (1814- 1874), Swedish physicist and astronomer] amu........... atomic mass unit (1.6605402 10-27 kg) are............ unit of area (1 are = 100 m2) arcmin......... arcminute [1' = (1/60)º or 1 arcmin = 2.908882 x 10-4 radian] arcsec.......... arcsecond [1” = (1/60)' or 1 arcsec = 4.848137 x 10-6 radian = 0.000278º] au............. astronomical unit - unit of length, namely the mean Earth/sun distance [=1.495978706 1013 cm, which is the semimajor axis of the Earth's orbit around the sun (or about 150 million km)] bar............ pressure, (1 bar = 105 Nm-2) Bq............. Becquerel [named after Alexandre Edmond Becquerel, a French physi­ cist (1820-1891)]. The Bq is a SI unit used to measure a radioactivity. One Becquerel is that quantity of a radioactive material that will have 1 transformations in one second. c.............. velocity of light in vacuum (299,792,458 m/s) cd............. candela (unit of luminous intensity). The candela is the luminous inten­ sity, in a given direction, of a source that emits monochromatic radi­ ation of frequency 540 × 1012 Hz and that has a radiant intensity in that direction of 1/683 watt per steradian. cm............ centimeter (unit of length) 1 cm = 10-2 m C.............. coulomb - unit of electrical charge; 1 C = 1 As [named after Charles- Augustin Coulomb (1736-1806), French physicist. The coulomb is the quantity of electricity transported in 1 second by a current of 1 ampere. ºC............. degree Celsius [named after Anders Celsius (1701-1744), Swedish as­ tronomer] dB............. decibel - a unit for expressing the signal strength [named after Alexan­ der Graham Bell (1847-1922), Scottish-born American inventor] dm............ decimeter (length) 1 dm = 10-1 m Dobson Unit.... 1 Dobson Unit equals the number of ozone molecules required to cre­ ate a layer of pure ozone 0.01 mm thick at a temperature of 0ºC and a pressure of one atmosphere. E.............. Eötvös (1 E = 10-9 s-2). The linear gradient of gravity is defined in units of Eötvös, named in honor of the Hungarian physicist Roland Eötvös (1848-1919). The Eötvös unit is used in geophysics to measure the rate of change, or gradient in the acceleration of gravity with hori­ zontal distance. Erlang......... a dimensionless unit of average traffic density (occupancy) of a facility (telecommunications system, data collection system, etc.) during a pe­ riod of time, usually a busy hour. Example: 60 calls in 1 hour, each last­ ing for 5 minutes = 300 minutes / 60 min per hour = 5 Erlang. Network designers use the Erlang to understand traffic patterns. eV............ electron volt (1.60217733 10-19 J). A unit of energy, equal to the energy an electron (or proton) would gain when accelerated by 1 volt. F.............. farad - a unit of capacitance [named after Michael Faraday (1791 -1867), English physicist and chemist]. The farad is the capacitance of a capacitor between the plates of which there appears a difference po­ 2 tential of 1 volt when it is charged by a quantity of electricity equal to 1 coulomb. f.............. focal length f/d............. focal-length-to-diameter ratio GHz........... Gigahertz (109 Hz) GWe........... Gigawatt (109 W) electrical energy gal............ unit of acceleration (used in particular in gravity measurements): 1 gal = 10-2 m s-2 = 1 cm s-2; 1 mgal = 10-5 m s-2 [named after Galilei Galileo (1564-1642), Italian mathematician, astronomer and physi­ cist]. The gal unit is used in making measurements of local variations in the acceleration of gravity g. Variations in the acceleration of Earth's gravity (e.g. gravity anomalies) are typically measured in milligal (mgal). One gal is approximately 0.0010197 g, or 1 gal is about 10-3 g. Hence, 1 mgal is about 10-6 g. gauss (G)....... unit of magnetic induction [named after Carl Friedrich Gauss (1777- 1855), German mathematician] Gy............ Gray [named after Louis Harold Gray (1905-1965) British physicist, president of BIR (British Institute of Radiology) and elected F.R.S. (Fellow of the Royal Society) in 1961]. The gray is a SI unit used to mea­ sure a quantity called absorbed dose. This relates to the amount of en­ ergy actually absorbed in some material, and is used for any type of radi­ ation and any material. One gray is equal to one joule of energy depos­ ited in one kg of a material (or: 1 gray = 1 J/kg). Note: In the SI system, the rad is replaced by the gray; 1 krad =10 gray. H............. henry - unit of magnetic inductance; 1 H = 1Wb/A or 1Vs/A [named after Joseph Henry, a nineteenth-century US physicist] Hz............ hertz - a measure of frequency; 1Hz = 1/s [named after Heinrich Ru­ dolf Hertz (1857-1894), German physicist]. In 1887, Hertz proved that energy is transmitted through a vacuum by electromagnetic waves. h.............. hecto (102) h (or hr)........ hour h.............. Planck's constant = 6.6260755 x 10-34 Js (joule second) ha............. hectare (1 ha = 104 m2) hPa............ hectopascal (international standard of pressure, 1 hPa = 100 Pa) Isp............ specific impulse with a unit Ns/kg. The numerical value of the specific impulse also corresponds to the effective exhaust velocity (m/s) of the gas exiting the thruster in a vacuum. See also Glossary. J.............. joule - unit of work or energy; 1 J = 1 Nm = 1 Ws [named after James Prescott Joule (1818-1889), British physicist] Jy............. “Jansky,” the unit of radio-wave emission strength or flux density (brightness of a radio source), in honor of Karl G. Jansky (1905-1950) an American engineer whose discovery of radio waves (1931) from an extraterrestrial source inaugurated the development of radio astrono­ my. Jansky published his findings in 1932 while working at Bell Tele­ phone Laboratories in Murray Hill, NJ, USA. The “Jy” is a unit of radiative flux density (or radio-wave emission strength) which is commonly used in radio and infrared astronomy. 1 Jy = 10-26 W/(m2 Hz). The units of Jy (Hz)-1/2 then refer to the noise power. K.............. degree Kelvin [named after Sir William Thomson (Lord Kelvin, 1824- 1907), Scottish engineer, physicist and mathematician]. The degree Kelvin is the unit of temperature determined by the Carnot cycle with the triple-point temperature of water defined as 273.15 K (corre­ sponds exactly to 0 ºC). k.............. kilo (103) kbit/s.......... kilobit per second (103 bit/s) keV........... kiloelectron volt (103 eV) 3 kg............. kilogram (103 g). The kg is a unit of mass. The kilogram is currently de­ fined in terms of the mass of a platinum-iridium artifact stored in France. Scientists want to replace this physical artifact with a more re­ producible definition for the kilogram that is based on fundamental constants of nature. — A new SI definition of the kg is due in November 2018. 7064) kg/m3 .......... density kHz........... kilohertz (103 Hz) km............ kilometer (103 m) krad........... kilorad (see rad below) kW............ kilowatt (103 watt) kWe........... kilowatt electric (used to distinguish electrical power from thermal power) L.............. liter (volume) 1l = 1 dm3 [the symbol for liter is capitalized (when alone by itself) to avoid confusion with the number 1] lm............. lumen (cd sr) luminous flux. The lumen is the luminous flux emitted in a solid angle of 1 steradian by a uniform point source having an intensity of 1 candela. lx.............. lux (lm/m2) illumination M............. Mega (106) mas............ milliarcsecond (1 mas = 4:848 x 10-9 rad) Mbit/s.......... Megabit per second (106 bit per second) MeV........... Megaelectron volt (106 eV) MHz........... Megahertz (106 hertz) Mpc........... Megaparsec (unit of length used in astronomy) Msample/s...... Mega sample/s (also written as Msps) m............. meter m............. milli (10-3) m2 ............. area (square meter) m3 ............. volume (cubic meter) marcsec........ milliarcsecond = 2.78º x 10-7 mb (mbar)...... millibar min............ minute mCrab......... “ 1 mCrab” is a unit to describe the X-ray intensity defined as 1/1000 of the intensity of the Crab nebula. X-ray astronomers use this unit when comparing observations from different X-ray detectors on different instruments. mg............ milligram (10-3 g) mgal........... milligal ` 10-6 g (where “g” is the gravity constant) mJ............ millijoule (10-3 J) ml............. milliliter (10-3 l) mm............ millimeter (unit of length) 1 mm = 10-3 m mN............ millinewton mrad........... milliradian 7065) ms............. millisecond m/s............ meter per second (velocity) m .............. micro (10-6) marcsec......... microarcsecond = 2.8º x 10-10 mgal........... microgal ` 10-9 g (where “g” is the gravity constant of 9.81 m/s2) mm............ micrometer (10-6 m) mrad........... microradian ms............. microsecond (10-6 second) _____________________ 7064) ”New measurement will help redefine international unit of mass,” Space Daily, July 3, 2017, URL: ht­ tp://www.spacedaily.com/reports/New_measurement_will_help_redefine_international_unit_of_mass_999.html 7065) An example is given to better visualize the plane angle of a milliradian. The apparent sun disk angle as seen from Earth is 32' 26” (max, or about 30.7 mrad), and 31' 31” (min) -- on average about 32 arcmin. 4 N............. newton - unit of force; 1N = 1 kgm/s2 [named after Sir Isaac Newton (1643-1727), English natural philosopher and mathematician] Nm............ newton meter (work or energy) Nms........... newton meter second (angular momentum) n.............. nano (10-9) nm............ nanometer (10-9 m) nm...........