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Define Astronomical unit, light year and parsec. |
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Answer» SOLUTION :Astronomical UNIT (AU) = Average distance between the Sun and the Earth is called astronomical unit. 1 AU = `1.496 xx 10^(11)` m Light Year : Distance travelled by light in vacuum in 1 year is called 1 light year. Speed of light in vacuum `C = 2.99 xx 10^(8) ms^(-1)` `:.`Distance travelled in 1 year =ct `=2.99xx10^(8)xx365xx24xx3600` `=9.46xx10^(15) m` Light year is used to measure distance between celestial objects. Parsec (pc): Distance at which average radius of earth.s orbit subtend angle of 1" (arc second) is called 1 parsec (pc).  From FIGURE `theta` (rad)= `(arc)/("radius")=(l)/(r)` `:.r=(l)/(theta)=(1AU)/(1..)` `(1AU=1.496xx10^(11)m)` `:.I..(1)/(60xx60)xx(pi)/(180)` (RADIAN) `:.r=(1.496xx10^(11))/(((1)/(60xx60)xx(pi)/(180)))` `:.r=3.08xx10^(16) m` 
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