Sir,<br/><br/>1.The <a href='http://en.wikipedia.org/wiki/Sidereal_year' target='_blank' rel='nofollow'>http://en.wikipedia.org/wiki/Sidereal_year</a> is the time taken<b> for</b> the Earth to complete one revolution of its <a href='http://en.wikipedia.org/wiki/Orbit' target='_blank' rel='nofollow'>http://en.wikipedia.org/wiki/Orbit</a>.<br/><br/>I am not able to understand the usage of "for " here.<br/>Normally, I would like to write the above sentence as<br/><br/>2. The <a href='http://en.wikipedia.org/wiki/Sidereal_year' target='_blank' rel='nofollow'>http://en.wikipedia.org/wiki/Sidereal_year</a> is the time taken<b> by</b> the Earth to complete one revolution of its <a href='http://en.wikipedia.org/wiki/Orbit' target='_blank' rel='nofollow'>http://en.wikipedia.org/wiki/Orbit</a>.<br/><br/>Does the meaning of (1) and (2) same?<br/><br/>Please explain about the usage of "for" in the sentence (1).<br/><br/>Thanks.