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Angular measure

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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.

[edit] Angular measurement
Using a marine sextant to measure the altitude of the sun above the horizon ...

Angular Measurement
The angle covered or subtended by something (measured in degrees, minutes of arc, seconds of arc), as opposed to linear size of something (measured in units of kilometers or parsecs).
angular momentum ...

A unit of angular measure equal to 60 arc minutes or 3600 arc seconds. One degree is equal to the diameter of two full Moons.
The amount of mass per unit of volume.

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).

the ship is sailing across the Pampas, the position in the Atlantic is the correct one. Note that the lines of position in the figure are distorted because of the map's projection; they would be circular if plotted on a globe.
Angular ...

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.

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 ...

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.

(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 consisting of 1/60th of an arc-minute. A dime seen from a distance of 2 miles transects 1 arc second. There are 3,600 arc-seconds in a one-degree angle.

A unit of solid (three-dimensional) angular measure. One steradian is equal to the angle subtended at the centre of a sphere by an area of surface equal to the square of 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.

A unit of angular measure equal to one sixtieth of one sixtieth of a degree, or one sixtieth of an arc-minute. As an example, the apparent diameter of Jupiter is about 45 arc-seconds.

So if the universe is "flat," meaning it's angular measurements have lines that stay parallel to each other, (assumedly in all 3 dimensions) wouldn't that make our universe more like an expanding box (or quadrilateral maybe), ...

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 ...

There are finer divisions of angular measure. A degree is made up of 60 arcminutes, and each arcminute is divided into 60 arcseconds.

True field - How much sky, in angular measure, is seen through an eyepiece.
Guide to Amateur Astronomy, Planets and Constellations ...

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 ...

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.

Problem 1 - Suppose that the Dawn spacecraft travels at a constant outward speed from Earth's orbit. If we approximate the motion of the spacecraft by X = R cosΘ, Y=RsinΘ and R = 1 + 0.08 Θ, where the angular measure is in radians, ...

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 ...

See also: See also: Astro, Earth, Sun, Planet, Sky

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