Where did the sun rise first on Earth?

Based on the time zone, the international date line, and the shift between the Sun and the Earth, the first place to catch the dawn will not be fixed.

The international date line (yellow line) defines the boundary between calendar dates. Photo: NOAA

On Earth, the Sun is constantly rising and falling on the horizon. So where does the first sunrise of the day happen? From a physics perspective, there's really no "first" dawn, according to Cameron Hummels, a postdoctoral researcher specializing in theoretical astrophysics at the California Institute of Technology. There's just a continuous sequence of dawns going farther and farther west - no real first or last.

However, to keep track of time, humans have established a system of time zones and the International Date Line (IDL) - an imaginary line on Earth that marks where one day ends and the next begins. head. "So, by agreement, the 'first' dawn of the day takes place at the international date line," Hummels explains.

The IDL passes through the middle of the Pacific Ocean, mainly running along the 180 degree meridian. The line is mostly straight, but has some twists and turns to avoid dividing a country into two time zones, or for political and economic reasons. For example, the IDL juts out nearly 3,200 km east through Kiribati, a nation of scattered islands at the equator. Kiribati has the earliest time zone on Earth, UTC +14 (Vietnam has time zone UTC +7).

"Most of the year, for example near the equinox (the time when the Earth's equator passes through the center of the Sun), Kiribati will see the first sunrise of the day," Hummel said. Specifically, the uninhabited Millennium island at the easternmost tip of Kiribati is often the first place on Earth to see dawn.

However, this is not always true. The Earth is tilted slightly by 23.5 degrees, so the way sunlight hits the blue planet during the year also changes. On the southern summer solstice and the north winter solstice (December 21 or 22), the Sun "prefers" to illuminate the Tropic of Cancer in the Southern Hemisphere, the South Pole and much of Antarctica being illuminated 24 hours a day.

"But if it moves above 66.6 degrees South, the Sun will dip below the horizon briefly before rising again a few minutes after midnight," Hummels said. Young Island in the Southern Ocean will sometimes see its first sunrise in the days around the solstice (when the Sun is furthest north or south of the equator), including January 1.

However, the probability of catching a sunset on this uninhabited island is only about 10% to 15%, according to the US Naval Observatory. The light refraction effect of Earth's atmosphere is so strong that one can continue to see sunlight on Young Island after the Sun has dropped below the horizon, preventing true sunset or sunrise. When this happens, the Dibble Glacier peninsula, on the coast of Antarctica, will see the first sunrise of the day at the solstice.

Around the northern summer solstice and the south winter solstice (June 20 - June 22), the Sun shines more directly into the Northern Hemisphere than the Southern Hemisphere. So the first dawn will deviate to the north. "The international date line winds its way between Russia and Alaska, passing through the Bering Strait. It divides the two islands of the Diomede Archipelago. In the weeks leading up to June 21, the Great Diomede Island saw the world's first sunrise." , Hummels said.