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Joe Blanton, director of our Research Correspondence staff, oversees the answering of 50,000 queries and comments addressed to the National Geographic Society annually. Each week he posts answers to three of the most interesting inquiries received online at Glad You Asked. Unfortunately, individual e-mail replies are impossible.

King of the Mountains ...

I have heard rumors that K2 rather than Mount Everest is indeed the tallest mountain in the world due to a miscalculation when it was originally measured. Is this true?

Here's the scoop: For years the official height of Mount Everest was 29,028 feet (8,848 meters). Early in 1987, a University of Washington astronomer made some preliminary measurements and found K2 (also known as Godwin Austin) to be some 33 feet (10 meters) higher than the figure for Everest. The news was leaked prematurely to the press, which began to run articles touting K2's new status as number-one mountain. An Italian team later remeasured both peaks using sophisticated satellite technology and found that Everest stands at 29,108 feet (8,872 meters)—80 feet (24.4 meters) higher than the previous measurement—while K2 measures 28,268 feet (8,616 meters). King Everest still reigns.

Incidentally, both mountains are gaining altitude. The continuing collision of the Eurasian and Indian-Australian plates deep beneath the earth's surface is raising the height of these famous peaks approximately two inches each year.

I have just been confronted with the statement that the Panama Canal has different sea levels in the Atlantic and Pacific Oceans. Therefore the canal needs three locks. Is this true? How big is the difference?

It's the tides, not the sea level, that cause the difference. The mean (average) sea level for the Atlantic and Pacific is virtually the same. But the tides on the Pacific end of the canal can rise and fall as much as 18 feet (5.5 meters). Over on the Atlantic side, the tides vary only about 2 feet (.61 meter). Were the canal at sea level, strong currents flowing through it propelled by the tidal variation would be disruptive to navigation. But that’s just one reason for the locks. Economics is another. Engineers would have faced a much bigger (and more expensive) job in digging out a sea level canal. Therefore, huge locks at either end of the canal were constructed to lift ships 85 feet (26 meters) above the level of the sea to where they can sail across man-made Gatun Lake.

Interestingly, the Pacific terminus of the Panama Canal at Balboa is actually 27 miles (43 kilometers) east of the Atlantic entrance, an anomaly caused by the reclining S-curve shape of the Isthmus of Panama. The sun rises there over the Pacific and sets over the Atlantic!

I am a bit confused about the time zones used in the U.S. Could you please tell me the full names of every time zone there, not just the usual abbreviations? Thanks for your answer! Here in Paris, France, it is now 09H00 CET (Central European Time) !!!!

It’s only been in the past hundred years or so that official time zones have existed. Prior to that, local regions in the United States adhered to their own local times. Noon came to your hometown when the sun was directly overhead. So when it was noon in Washington, D.C., it was already 12:08 in Philadelphia, 12:12 in New York, and 12:24 in Boston. In Atlanta, it was still only 11:30 a.m.

All that changed on November 18, 1883. That was the day when, at the instigation of the railroad industry, the United States adopted four now familiar time zones: Eastern, Central, Mountain, and Pacific. During half of the year, each of these appellations is followed by the words “Standard Time” as in Eastern Standard Time (EST). During the half-year when daylight saving time is observed, we have Eastern Daylight Time (EDT), etc.

Our newest states, Alaska and Hawaii, have time zones of their own. Most of Alaska rests in the Alaska Time Zone, while that state’s Aleutian Islands share time with Hawaii in the Hawaii-Aleutian Time Zone.

Although I might have suspected it, having commuted for years in Washington, D.C., rush-hour traffic, I was a bit surprised to learn that 50 percent of the U.S. population lives in the Eastern Time Zone.