Astrophysics (Index) About

### 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). Another criterion, the Dawes limit aka Dawes criterion, is essentially the same criterion specific to optical telescopes, based on a wavelength within the optical range (about 460 nm, which is blue).

```R = 4.56/D
```

R is arcseconds and D is in inches (4.56 inches equals 115.824 mm so 116 is an equivalent constant for millimeters).

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 (based on Rayleigh criterion):

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

(telescopes,optics,measure,specification)
Further reading:
http://en.wikipedia.org/wiki/Angular_resolution
http://en.wikipedia.org/wiki/Dawes%27_limit

Referenced by pages:
Atacama Cosmology Telescope (ACT)
Airy disk
aperture masking interferometry (AMI)
aperture
aperture synthesis
apodization
Archeops
ASCA
astrometry
Australia Telescope Compact Array (ATCA)
baseline
beam
blind survey
Large Altazimuth Telescope (BTA-6)
C-BASS
CHARA
chromatic aberration
collecting area
Compton telescope
CONCERTO
confusion limit
correlator
COSMOSOMAS
counterpart
CRATES
diffraction limited
EMPIRE Survey
EPOXI
extended source
Fourth Cambridge Catalog of Radio Sources (4C)
field of view (FOV)
Galactic All-sky Survey (GASS)
Hale Telescope
HARMONI
HEAO-2
high-resolution imaging
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
PHANGS
PHIBSS
plate scale
point source
PSF fitting
radio astronomy
RATAN-600
RELIKT-1
ROSAT
surface brightness fluctuation (SBF)
SCUBA
Sloan Digital Sky Survey (SDSS)
seeing
SOAR
solar telescope
Solar Orbiter (SolO)
speckle imaging
speckle masking
speckle suppression
Spektr-R
SPHEREx
stellar distance determination
Subaru Telescope
SUSI
Uhuru
VERA
Very Long Baseline Array (VLBA)
very-long-baseline interferometry (VLBI)
WIYN 3.5m Telescope

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