How will you ‘weigh the sun’, that is estimate its mass? The mean orbital radius of the earth around the sun is 1.5 × 108 km.


We know that earth revolves around sun in elliptical orbit due to gravitational force applied by sun, we also know that in one complete revolution earth takes 365.25 days and we are given mean orbital radius of earth around sun, now we know that If a body orbits around other heavier body due to gravitational force of attraction then we have a relation between mass of heavier body, time period of revolution and, radius of the orbit as


Where M is the mass of the heavier body, R is the radius of the orbit, G is universal gravitational Constant and T is time period of revolution


Now here unknown mass is mass of the sun, M =?


Orbital radius of earth around sun, R = 1.5 × 108 km


Time period of one revolution, T = 365.25 days


Converting into seconds


1 day = 24 hours


1 hour = 60 minutes


1 minute = 60 seconds


So we get time of 1 year as


T = 365.25 × 24 × 60 × 60 s = 3.15 × 107 s


Value of universal gravitational Constant


G = 6.67 × 10-11 Nm2Kg-2


Putting these values in above relation



Solving we get the mass of sun as 2.0 × 1030 Kg


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