Angular Measurements
In astronomy, we often use angular measurements to describe the apparent size of an object in space and the apparent distances between objects. Often these angles are very small.
Angular measurement
Accurate angle measurement evolved over the years. One simple method is to hold the hand above the horizon with your arm stretched out. The width of a finger is an angle just over 1.5 degrees.
Angular Measures
Objects look bigger when they are closer to us. If the distance between an object and the observer is halved, the apparent size of the object will be doubled.
[edit] Angular measurement
Using a marine sextant to measure the altitude of the sun above the horizon ...
The unit of angular measure, defined as the ratio of a length of arc intercepted by two radii to the length of the radius. P radians = 180°.
radiant - (n.)
The point in the sky from which all the meteors in a meteor shower appear to be coming.
Spacecraft Angular Measurement
The spacecraft's position in the sky is expressed in the angular quantities Right Ascension and Declination.
A radian is an angular measurement.
If we draw two straight lines that cross at the centre of a circle such that the length of the circumference between them (an arc) equals the radius, then the angle between these lines is 1 radian.
mil: unit of angular measurement used in some military equipment, e.g. rangefinders, theodolites. 6400 mils = 360º. Beware possible confusion with use as a linear measurement of 1/1000 inch used by engineers (particularly in the USA).
...
degree A unit of angular measure. There are 360 degrees in a complete circle.
density A measure of the compactness of the matter within an object, computed by dividing the mass by the volume of the object.
arc-second
An angular measurement. There are 60 arc-seconds in one arc-minute, 60 arc-minutes in one degree, and 360 degrees in a full circle. One thousandth of an arc-second = 1 milliarc-second.
Related category
- UNITS ...
Hour Angle The angular measure of the distance of an object from the local meridian.
Setting circles are angular measurement scales that can be placed on the two main rotation axes of some telescopes.
The phase difference of two periodically recurring phenomena of the same frequency, expressed in angular measure. 2. The angle at a celestial body between the sun and earth. phase constant See propagation constant.
difference of latitude (NASA SP-7, 1965) The shorter arc of any meridian between the parallels of two places, expressed in angular measure.
Arc Degree A unit of angular measure in which there are 360 arc degrees in a full circle.
Arc Second Abbreviated arcsec.
MORE PRECISELY 1-1Angular Measure
The size and scale of things are often specified by measuring lengths and angles. The concept of length measurement is fairly intuitive.
Recall that the total angular measure around a circle is 360 degrees. The angle from (say) the eastern to western horizon (through the point directly overhead, the zenith) is 180 degrees.
The word "arc'' is added to denote angular measure rather than time. For example, the diameter of the Moon is about 30 arcminutes.) This linear distance had increased by about 50 percent by the time the comet was lost in the glare of the Sun in July ...
(b) A unit of angular measure equal to the angle subtended at the centre of a circle by an arc the length of which is equal to the radius.
A unit of angular measure in which there are 60 arc seconds in 1 arc minute and therefore 3600 arc seconds in 1 arc degree. There are 206,265 arcseconds per radian. One arc second is equal to about 725 km on the Sun.
RADIAN - A radian is an angular measurement. The angular circumference of a circle is 2π radians, or 360°; thus, 1 radian = 360/2π degrees = 57.29578° (57° 17' 44.8").
radian; rad
The supplementary SI unit of angular measure, defined as the central angle of a circle whose subtended arc is equal to the radius of the circle. One radian is approximately 57o.
Minute of Arc - A unit of angular measurement equal to 1/60 of a degree
Mode of Oscillation - A particular pattern of vibration of the Sun
Molecular Cloud - A relatively dense, cool interstellar cloud in which molecules are common ...
f. It is convenient to be able to convert between angular measurement and sidereal time measurement. Twenty four (24) hours is equivalent to 360 degrees. From this we can produce the following conversions.
Time measurement Angle measurement ...
second of arc: An angular measure; each minute of arc is divided into 60 seconds of arc.
secondary atmosphere: The gasses outgassed from a planet's interior; rich in carbon dioxide.
The word arc is added to denote an angular measure rather than time. The diameter of the Moon is near 30 arc minutes, for example, while the apparent diameter of Jupiter when closest to Earth is 50 arc seconds.) The comet's brightness was reported ...
One sixtieth of a degree of angular measure. The Moon is 31 arcminutes across. [C95]
Archiving
Making a permanent record which can be accessed later at any time. [McL97]
Arcsecond ...
Declination: Celestial coordinate which is equivalent to the latitude of an object on Earth. This is an angular measure of how far above the celestial equator an object lies.
The determination of distances and motion along the line of sight is another branch of astronomy, although purely angular measurements within the solar system combined with a knowledge of masses of the planets etc can lead to a complete description ...
Sharaf al-Din al-Tusi invented the linear astrolabe, sometimes called the "staff of al-Tusi", which was "a simple wooden rod with graduated markings but without sights. It was furnished with a plumb line and a double chord for making angular ...
The six orbital elements used for comets are usually the following: time of perihelion passage (T) [sometimes taken instead as an angular measure called "mean anomaly", M]; perihelion distance (q), usually given in AU; eccentricity (e) of the orbit; ...
 See also: Degree, Earth, Distance, Sky, Planet
|
