Michelson Stellar Interferometer is used to measure:

Interferometer:

• It is a device which performs higher resolution image of astronomical instruments like stars, planets etc. 
• It is basically an array of many telescopes. antennas and other minor segments. 
• It works on the principle of interference of light. 
• Albert A. Michelson in 1890, made an interferometer which is considered as one of the earliest. 

Working of Interferometer 

• Constructive interference occurs, when peaks and troughs of two (or more) waves perfectly coincide and destructive occurs, when the peak of one wave coincides with another's trough.
• Interferometer detects the imperfections in perfectly constructive or destructive interferences. 

Measuring distance by Michelson Stellar

• A Michelson interferometer has two mirrors M1 & M2 and a beam splitter M.
• A light emitted from S hits the beam splitter surface M at point C.
• M being partially reflective, part of transmitted through to point B is reflected in the direction of A.
• Both beams recombine at point C' to produce an interference pattern incident on the detector at point E (or on the retina of a person's eye).
• If a slight angle is observed between the two returning beams  then the imaging detector will record a sinusoidal fringe pattern
• If there is perfect spatial alignment between the returning beams,(perfect interference)  then there will not be any such pattern
• A constant intensity over the beam dependent on the differential path length is observed in that case.

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