Indian Standard Time Meridian 82°30 E Of greenwich shows the time five hours and 30 minutes ahead off GMT. Calculate what time it is in London if it is 8:30 PM in India.
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Answers
Explanation:
The GMT time standard concerns noon*.
Local noon in India happens 5:30 hours before local noon in London (offset GMT+5:30).
But to help you understand and visualise GMT offsets, it is best to think about where instead of when.
India enjoys solar noon at 5.5 hrs x 15 degrees = 82.5 longitude. As the earth turns India into afternoon London will lay underneath the sun at longitude 0 (GMT+0).
{TL:DR } India is wide enough to span multiple time zones but has chosen the convention and practicality of using just one, China also has a single time zone. Russia however uses more than 9.
Time zones are a political matter before they are geographic.
Greenwich noon is notional since the actual position of the sun varies due to the ecliptic motion of the earth. It is therefore a “Mean” noon which negates the effect of the earth’s orbit and longitude, so that people can agree on current time. The actual noon and GMT noon will only coincide four times in the year, at cardinal points of equinox and solstice. The reconciliation between solar time and civil time is called the Equation of Time: