1 Candela (Cd) (unit of light intensity). The luminous intensity of a light source producing single-frequency light at a frequency of 540 terahertz (THz) with a power of 1/683 watt per steradian - or 18.3988 milliwatts over a complete sphere centered at the light source. 540 THz ≈ 555.17 nanometers (nm). Candle (cd) is older name – obsolete.
1 Mole (Mol) (unit of amount of substance - as distinct from its mass or weight, or the actual number of atoms or molecules in an object. 1 mole of a substance contains just as many elementary entities (atoms, molecules, ions, or other kinds of particles) as there are atoms in 12 grams of carbon-12 (having 6 protons and 6 neutrons). The actual number of "elementary entities" in a mole is called Avogadro's number ≈ 602.214179 x 10²¹.
1 Joule (J) (unit of work or energy)
≈ 2.777 778 x 10^-4 watt hour
= 10⁷ ergs
≈ 0.737 562 foot-pound
≈ 9.478 170 x 10^-4 Btu
≈ 0.238 846 calories
1 Lumen (Lm) (unit of flux of light produced - or received by a surface)
= 1 candela light
= 4·pi lumens
1 Lux (Lx) (unit of illumination (illuminance) of a surface)
= 1 lumen per square meter
= 0.0001 phot
= 1 lumen/square meter
≈ 0.09290 foot candle
1 Newton (N) (unit of force)
= 10⁵ dynes
≈ 0.224 809 pounds of force (lbf)
≈ 7.233 01 poundals
≈ 0.101 972 kilograms of force (kgf) or kiloponds (kp)
1 Radian (Rad) (unit of angle). The angle at the center of a circle that cuts off an arc of length equal to the radius.
= 1/(2 pi) of the circle
≈ 57.295 779°
Length of an arc (of a circle)
= radius of same circle
Area of a sector of a circle
= (½ r²) angular measure in radians
1 Steradian (Sr or Ω) (unit of solid angle)
≈ 0.079 577 sphere (there are 4pi steradians in a sphere)
≈ 3282.806 square degrees (there are 129 600/pi
= 41 252.96 square degrees in a sphere)
1 Degree of Angle (o or deg) (unit of angle)
= 1/360 circle, 60 minutes, 3600 seconds, or ≈ 0.017 453 293 radian
1 Minute of Angle (¢, minute, ′, m, moa, minute of arc or arcminute - unit of angular measure)
= 60 arcseconds
= 1/60 degree (there are 21600 arcminutes in a circle)
≈ a target size of 1 inch at 100 yards
= 1.047 20 inches at 100 yards
= 10.4720 inches at 1000 yards
= 2.9089 centimeters at 100 meters
1 Second of Angle (¢¢, arcsecond, ″, as, sec, s, or second of arc - unit of angular measure)
= 1/60 arcminute (there are 1 296 000 seconds in a circle)
1 milliarcsecond (mas) (unit of angular measure - astronomy)
= 0.001 arcsecond
= 0.27777 microdegrees
= 4.848137 nanoradians
1 Second (s, sec, or ") (1- unit of time)
= that period of time which makes the frequency of a certain radiation emitted by atoms of cesium-133 equal to 9 192 631 770 hertz (cycles per second).
1 Second (s, sec, or ") (2- unit of angular measure – above)
1 Second (s, sec, or ") (3- unit of longitude – astronomy). Astronomers measure right ascension in time units by dividing the equator into 24 hours instead of 360 degrees. (Right ascension is the longtitude coordinate for positions in the sky; see hour). This makes 1 second of longitude equal to 15 arcseconds.
1 Second (sec or ") (4- unit of viscosity) is the time required for a specified amount of a liquid to flow through a particular viscometer. The “Saybolt second” was used in the U.S., the “Redwood second” in Britain and the “Engler degree” in continental Europe.
1 Second (s or sec) (5- unit of fuel efficiency of rocket engines). The measure is obtained as the thrust of the engine divided by the weight of fuel consumed per second (weight being measured at the earth's surface, or at 1 g). Since both thrust and weight are forces, their units cancel and the ratio is measured in seconds. This ratio is often called "specific impulse," although the true specific impulse (measured in speed units) is the ratio of the thrust to the mass (not weight) of fuel consumed per second.
1 Second (s or ") (6- unit of sidereal time – astronomy). Sidereal Day is a unit of time used in astronomy, equal to the period of time in which the earth makes one rotation relative to the stars. If we could view the earth from outside the Solar System, we would see that it actually completes 366.242 rotations during one year (one revolution around the sun). We only count 365.242 because one rotation is cancelled out for us by our tour around the sun. Thus the sidereal day, the average interval between two successive risings of the same star, is shorter than the mean solar day (see day) by 1/366.242. The sidereal day equals 23 hours 56 minutes 4.090 54 seconds, or 86 164.090 54 seconds. Like the regular day it is divided into 24 sidereal hours, each sidereal hour being divided into 60 sidereal minutes and each sidereal minute into 60 sidereal seconds. The sidereal hour equals 59 minutes 50.17 seconds; the sidereal minute equals 59.8362 seconds, and the sidereal second equals 0.997 270 second. Traditionally, observatories had clocks set to this sidereal cycle, and astronomers still use sidereal time in making telescope settings.