The islands are genuinely close.
Big Diomede and Little Diomede face each other across a narrow section of the Bering Strait. The U.S. National Park Service describes the separation as roughly 2.7 miles.
Globe Curiosities · Bering Strait
Two islands sit within sight of each other between Alaska and Russia. The water separating them is only a few kilometers wide — but the calendar can be almost an entire day apart.
01 · One narrow strait
The Diomede Islands time difference is one of the clearest examples of how political borders, time zones and the International Date Line can change our perception of distance. Big Diomede belongs to Russia. Little Diomede belongs to the United States. They sit only a few kilometers apart in the Bering Strait.
Yet they occupy opposite sides of the International Date Line. Big Diomede uses Anadyr Time at UTC+12. Little Diomede follows Alaska time, which is UTC−9 in standard time and UTC−8 while daylight saving time is in effect.
02 · The gap
Simplified geographic diagram for explanation. Island shapes and spacing are schematic, not to scale.
03 · Same moment
These clocks show the same instant on opposite sides of the Bering Strait. The unusual part is not how far apart the islands are. It is where the calendar boundary runs between them.
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04 · Why it happens
Nothing physical happens to time in the water between the islands. The dramatic jump comes from the systems people use to organize clocks and calendars around a rotating planet.
Big Diomede and Little Diomede face each other across a narrow section of the Bering Strait. The U.S. National Park Service describes the separation as roughly 2.7 miles.
The International Date Line separates calendar dates. Crossing it changes the date even when the physical distance traveled is small.
Russia's Big Diomede follows UTC+12. Little Diomede follows Alaska time. That creates a 21-hour difference during Alaska standard time and a 20-hour difference during daylight saving time.
05 · Yesterday and tomorrow
Little Diomede is often called “Yesterday Island” because it lies on the American side of the calendar divide.
Big Diomede is often called “Tomorrow Island.” At many moments, its local calendar date is already the following day.
06 · A useful detail
The International Date Line does not automatically create a 24-hour difference everywhere it passes. Local time-zone choices matter too.
Big Diomede remains on UTC+12 throughout the year. Little Diomede follows Alaska's seasonal clock changes. As a result, the difference between the two islands is normally either 20 or 21 hours, depending on the time of year.
Geography tells us where two places are. Time zones tell us how societies label the same moment. The Diomede Islands make the difference unusually easy to see.
07 · A line on more than a map
The channel between the islands is also an international border between the United States and Russia. In suitable winter conditions, sea ice can form between the islands, but that does not turn the route into an open pedestrian border crossing.
The contrast is what makes the islands remarkable: physically close, politically divided and separated by one of the world's most important calendar boundaries.
08 · Methodology
Distances between small islands vary slightly depending on the points used for measurement. The U.S. National Park Service describes Little and Big Diomede as approximately 2.7 miles apart. This page therefore uses approximately 4.3 km as an easy-to-read geographic comparison.
The time comparison uses the current civil time-zone rules: Anadyr Time for Big Diomede and Alaska Time for Little Diomede. The live clocks above use the visitor's browser to calculate both time zones at the same instant.
The island diagram above is intentionally schematic. It explains the relationship between the islands, international border and Date Line; it is not a navigational chart.
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