Explain: (i) spectroscopic method; (ii) kepler's method; (iii) copernicus method

These are the indirect methods of distance measurement.

Spectroscopic method: By measuring the Doppler shift in the spectrum of light received from a distant star, we can infer the distance of the star and it's recessional velocity from earth.

Kepler's Method: By using the Kepler's third law, we can measure the distance of a planet. We have to record it's time period to use this method, against a known time period and distance data for a planet.

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