How large a telescope is needed to just resolve this star at a wavelength of 550nm?

The star Betelgeuse is a supergiant with distance 150 pc and a radius equal to the radius of the earth's orbit about the sun. How large a telescope is needed to just resolve this star at a wavelength of 550nm? At a wavelength of 5 microns? (Consider diffraction-limited observations only, and ignore seeing. Note: 1 pc = 1 parsec = 3.1 x 10^13 km)|||1 AU/ 150 pc = 1/150 arcsec = 胃


sin胃 = 3.23 x 10^-8


位 = 5 x 10^-6 m


sin胃 = 1.22 位 / D


D = 1.22 位 / sin胃 = 189 meters.





However, there is some tricks used by astronomers to improve resolution. One trick is to deliberately defocus the telescope slightly to spread the light so no pixel gets saturated with too much light. Then, they correct the focus digitally to get a sharp image.