Time Difference between Greenwich and East
In order to determine the time in East when it is 12 am in Greenwich, we need to consider the time zone difference between the two locations. Greenwich Mean Time (GMT) is the standard time against which all other time zones are referenced.

Time Zones
- Greenwich Mean Time (GMT) is the time zone at the Prime Meridian in Greenwich, England.
- East could refer to a number of different locations depending on context, but for the sake of this explanation, let's assume it refers to Eastern Standard Time (EST) in the United States.

Time Difference
- Greenwich Mean Time is 5 hours ahead of Eastern Standard Time. This means that when it is 12 am in Greenwich, it is actually 7 pm in East.

Calculation
- To calculate the time difference, you subtract the time zone offset of East from GMT. In this case, 12 am GMT minus 5 hours equals 7 pm EST.

Conclusion
Therefore, when it is 12 am in Greenwich, it is 7 pm in East due to the 5-hour time zone difference between the two locations. It is important to consider time zone variations when coordinating activities across different regions to ensure accurate timing.