### angular resolution

(spatial resolution, resolution)
(measure of a telescope's ability to distinguish spatial detail)

Angular resolution is a measure of the ability of a telescope (optical, radio, etc.) to distinguish spatial detail. "Angular" refers to the measure describing an angle between two distinguishable features of an image with the observer as the vertex of the angle. The physics of diffraction determines a minimum angular resolution of a telescope based upon the size of its aperture. A point of light becomes a disk surrounded by rings if light (known as an Airy disk), and if the angle between two such points is sufficiently small, the disks are not distinct. Lord Rayleigh's Rayleigh criterion describes a telescope's resolution by the distance between two points such that one's disk maximum coincides with the adjacent disk's minimum, which the following formula calculates:

```           λ
θ = 1.220 ———
D
```

θ is the angular resolution (radians), λ is the wavelength, and D is the aperture diameter (both in same unit, e.g., meters).

With multiple telescopes arranged as an interferometer, smaller angular resolution can be obtained. Also, computer-based analysis on the overlapping Airy disks can sometimes identify and locate individual sources, achieving higher angular resolution than the Rayleigh criterion would imply. The term speckle suppression includes this and other methods of surpassing the Rayleigh criterion.

Example angular resolutions:

(Spektr-R's 10m dish limits it to bright radio sources.)

(telescopes,optics,measure,specification)
http://en.wikipedia.org/wiki/Angular_resolution

Referenced by:
Atacama Cosmology Telescope (ACT)
Airy disk
aperture
aperture synthesis
apodization
astrometry
Australia Telescope Compact Array (ATCA)
baseline
blind survey
Large Altazimuth Telescope (BTA-6)
C-BASS
CHARA
confusion limit
correlator
CRATES
diffraction limited
EMPIRE Survey
EPOXI
Fourth Cambridge Catalog of Radio Sources (4C)
field of view (FOV)
Galactic All-sky Survey (GASS)
Hale Telescope
HEAO-2
integral field unit (IFU)
imaging spectrometer
interferometer
interferometry
Keck Observatory
Large Millimeter Telescope (LMT)
lucky imaging
Lynx
Mars Express
millimeter astronomy
Mars Reconnaissance Orbiter (MRO)
optical interferometer
parallax
PAWS
PHIBSS
plate scale
PSF fitting
ROSAT
surface brightness fluctuation (SBF)
SCUBA
Sloan Digital Sky Survey (SDSS)
seeing
speckle suppression
Spektr-R
SPHEREx
stellar distance determination
Subaru Telescope
Uhuru
VERA
Very Long Baseline Array (VLBA)
very-long-baseline interferometry (VLBI)

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