Editing Optical telescope (section)

===Surface resolvability===
The smallest resolvable surface area of an object, as seen through an optical telescope, is the limited physical area that can be resolved. It is analogous to [[angular resolution]], but differs in definition: instead of separation ability between point-light sources it refers to the physical area that can be resolved. A familiar way to express the characteristic is the resolvable ability of features such as [[Moon]] craters or [[Sun]] spots. Expression using the formula is given by twice the resolving power <math>R</math> over aperture diameter <math>D</math> multiplied by the objects diameter <math>D_{ob}</math> multiplied by the constant <math>\Phi</math> all divided by the objects [[apparent diameter]] <math>D_{a}</math>.<ref name="SaharaSkyObservatory">{{cite web|url=http://www.saharasky.com/saharasky/formula.html|title=Telescope Formulae|date=3 July 2012|publisher=SaharaSky Observatory}}</ref><ref name="RyukyuAstronomyClub">{{cite web|url=http://www.nexstarsite.com/_RAC/form.html|title=Optical Formulae|date=2 January 2012|publisher=Ryukyu Astronomy Club}}</ref>

''Resolving power <math>R</math> is derived from the [[wavelength]] <math>{\lambda}</math> using the same unit as aperture; where 550 [[nanometers|nm]] to mm is given by: <math>R = \frac{\lambda}{10^6} = \frac{550}{10^6} = 0.00055</math>.''
<br />''The constant <math>\Phi</math> is derived from [[radians]] to the same unit as the object's [[apparent diameter]]; where the Moon's [[apparent diameter]] of <math>D_{a} = \frac{313\Pi}{10800}</math> [[radians]] to [[arcseconds|arcsecs]] is given by: <math>D_{a} = \frac{313\Pi}{10800} \cdot 206265 = 1878</math>.''

An example using a telescope with an aperture of 130&nbsp;mm observing the Moon in a 550 [[nanometer|nm]] [[wavelength]], is given by: <math>F = \frac{\frac{2R}{D} \cdot D_{ob} \cdot \Phi}{D_{a}} = \frac{\frac{2 \cdot 0.00055}{130} \cdot 3474.2 \cdot 206265}{1878} \approx 3.22</math>

The unit used in the object diameter results in the smallest resolvable features at that unit. In the above example they are approximated in kilometers resulting in the smallest resolvable Moon craters being 3.22&nbsp;km in diameter. The [[Hubble Space Telescope]] has a primary mirror aperture of 2400&nbsp;mm that provides a surface resolvability of Moon craters being 174.9 meters in diameter, or [[sunspots]] of 7365.2&nbsp;km in diameter.