The Greenwich Mean Time is the local time at :

Question

Accepted Answer

Greenwich Mean Time (GMT) is the mean solar time at the Prime Meridian, which is located at 0° longitude. This is why Option 4, "Prime Meridian," is the correct answer. Let's delve into the reasoning:

1. **Explanation for Option 4 (Prime Meridian):**
   - The Prime Meridian is the reference line for GMT, established at the Royal Observatory in Greenwich, London. It serves as the starting point for the world's time zones. GMT is used as a baseline for timekeeping and is crucial for coordinating time across different regions. The Prime Meridian is internationally recognized as the line of 0° longitude, making it the logical and factual basis for GMT.

2. **Why the other options are incorrect:**
   - **Option 1 (180° East Meridian):** The 180° East Meridian is not related to GMT. Instead, it is part of the International Date Line, which is used to determine the change of calendar days. It is located on the opposite side of the Earth from the Prime Meridian and does not serve as a reference for GMT.
   - **Option 2 (180° West Meridian):** Similar to Option 1, the 180° West Meridian is also part of the International Date Line. It does not have any connection to GMT, as GMT is specifically tied to the Prime Meridian at 0° longitude.
   - **Option 3 (180° East and 180° West both Meridians):** This option incorrectly combines the two meridians associated with the International Date Line. Neither of these meridians is used for GMT, as GMT is solely based on the Prime Meridian.

In summary, GMT is defined by the time at the Prime Meridian, making Option 4 the only correct choice. The other options are related to the International Date Line and have no bearing on the determination of GMT.