Anyone who moves to Boston can expect to be told within the first few weeks that — along with Fenway Park, the Isabella Stewart Gardner Museum and the glass flowers at Harvard’s Museum of Natural History — they really should check out the Mapparium. It’s customary to nod and express thanks for this suggestion, but it’s often years before those newcomers bother to ask: “What on Earth is a Mapparium?”

The Mapparium is a three-dimensional map of the Earth, free from any kind of cartographic distortion because, like the planet itself, it is a sphere. Located in the Mary Baker Eddy Library — which is part of the dauntingly vast Christian Science Plaza in Boston’s Back Bay — it’s three stories high, and was finished in 1935.

Enchantingly, it is made out of stained glass: 608 glass panels, to be precise. Each one represents 10-degree divisions of latitude and longitude. All this is illuminated from behind by a sophisticated system of LED lights. (Originally, the glass was lit by about 300 40- and 60-watt electric bulbs, which created uncomfortable levels of heat and needed regular replacement.)

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To get inside this impressive orb, you join a tour. They run every 20 minutes, daily, between 10 a.m. and 5 p.m. After a brief introduction, you walk into the Mapparium along a glass bridge that’s 30 feet long. What you see is a bygone world in three dimensions, experienced from an unusually privileged perspective. You’re at the center. It’s all around you.

Psychologically, this has a strange effect. Everything seems surprisingly close to everything else. You can see and feel the proximity of cities and countries that had seemed, in your imagination, immensely far apart.

The Mapparium — originally called the “Glass Room” or the “Globe Room” — was the bright idea of Chester Lindsay Churchill. Churchill was the architect who designed the Christian Science Publishing Society building, home to the respected Christian Science Monitor newspaper. The Monitor was founded in 1908 by Mary Baker Eddy (1821-1910), who was also the originator of Christian Science, a worldwide spiritual movement whose adherents seek a return to early Christianity’s emphasis on healing through prayer. (Baker believed, controversially, that illness is an illusion.)

Just as newspapers like to advertise their ambition and “world-consciousness” by including the word “globe” or “world” in their title, Churchill thought his “mapparium” would speak to the Christian Science Monitor’s mission, which was, in part, to provide an antidote to the dominance of so-called “yellow journalism” — journalism based on sensationalism and exaggeration. (Gee, glad those days are over.) The idea came to him after seeing a smaller globe in the headquarters of the New York Daily News in the 1930s.

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There are two important consequences of the Mapparium’s being made from glass. The first is obvious. Glass is beautiful, but fragile. It’s hard not to project that awareness onto the world as you contemplate it.

What’s more, glass doesn’t absorb sound. So when you are in the Mapparium, you are also in a whispering gallery. It is a whispering gallery unlike any other because it is a whole sphere, not just a dome. The volume of your voice is strikingly amplified at the center. And if you are near the edge, you can whisper softly, and someone on the opposite side will hear you with ease.

The Mapparium’s map is political, based on Rand McNally maps, which in 1935 were as up-to-date as possible. But of course, names and borders change, and it was rendered quickly out of date. In fact, just two months before the Mapparium’s schedule opening in 1935, Persia changed its name to Iran, and the artisans had to scramble to make the change. (Unconvinced, perhaps, that the new name would stick, they hedged by placing “Persia” in parentheses under “Iran.”)

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It’s stunning to see how much the political map has changed since 1935. Thailand appears as Siam, Vietnam as French Indochina. Russia and its neighbors appear as the Soviet Union. Did you ever learn in geography class about Italian Somaliland? I know I didn’t, perhaps for the good reason that in 1936 — a year after the Mapparium opened — Italian Somaliland merged with Italian Eritrea and the newly occupied Ethio­pian Empire to become Italian East Africa.

The map’s colors are keyed largely to colonial realities: France is green, as are its territories in Africa, Asia and the Pacific. Great Britain is red, along with huge swaths of territory all over the globe. It’s sobering to register the extent and pervasiveness of colonialism so far into the 20th century.

The original intention was to remove glass panels with redundant names or borders and replace them on a regular basis with more up-to-date information. This never happened. The Church considered an overhaul in 1939 (probably a good thing it waited) and then again in 1958 and 1966. But the idea was rejected each time, and gradually, the Mapparium came to be seen as a historical artifact. Like everything else these days that doesn’t turn out quite as planned, it has been assigned a new value as a “teachable moment.”

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The Mapparium at the Mary Baker Eddy Library, 200 Massachusetts Ave., Boston. marybakereddylibrary.org/project/mapparium.

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