90th meridian east, line of longitude east of the Greenwich Meridian
The 90th meridian east is a line of longitude that runs from the North Pole to the South Pole, positioned exactly 90 degrees east of the Prime Meridian. It crosses Russia, Mongolia, China, Bhutan, India, and Bangladesh before continuing across the Indian Ocean and into Antarctica.
The 90th meridian east became a recognized geographic reference when standardized coordinate systems were adopted internationally during the 19th century, giving cartographers and navigators a consistent tool. Before that, each nation often used its own reference meridian, so agreement on shared lines like this one was a significant step in global mapping.
The 90th meridian east passes through regions where daily life looks very different from one place to the next, shaped by the land and the seasons. Visitors moving along this line can observe how local customs, building styles, and land use shift dramatically from the Mongolian steppe to the river deltas of Bangladesh.
The meridian itself is invisible and has no physical presence on the ground, so it is used mainly as a reference on maps and navigation tools. Those who want to visit places along its path should check entry requirements and local conditions well in advance, as the countries it crosses have very different travel rules.
Beneath the Indian Ocean, this line of longitude runs almost directly above the Ninety East Ridge, a long underwater mountain chain formed by volcanic activity. Scientists have studied this formation to better understand how monsoon patterns developed and how ocean currents shifted over millions of years.
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