Why total solar eclipses are so special

[00:00:04]Legend has it that a savage battle between the Lydians and Medes came to a sudden standstill.

[00:00:11]Weapons dropped to the ground as the men looked up to the sky in terror and awe.

[00:00:18]The sun, which only moments before shown high above them, had vanished.

[00:00:25]This omen caused both sides to lay down their arms and declare a truce.

[00:00:32]What the Lydians and Medes experienced that day was a total solar eclipse.

[00:00:38]Eclipses occur when astronomical objects align.

[00:00:43]The alignment of the sun, moon, and Earth creates [music] a solar or lunar eclipse.

[00:00:50]But even though the moon orbits the Earth every month, solar eclipses don't happen that often.

[00:00:57]That's because the moon's orbit is tilted by about 5° [music] compared to the Earth's path around the sun. Most of the time, >> [music] >> it passes slightly above or below the sun in our sky.

[00:01:12]Twice a year, the moon's orbit crosses the sun-Earth line. These are called lunar nodes.

[00:01:20]When a new or full moon occurs near one of these nodes, we get [music] an eclipse.

[00:01:27]A lunar eclipse happens when Earth moves between the sun [music] and the moon, casting its shadow on the moon's surface.

[00:01:34]Sunlight passing through Earth's atmosphere scatters and turns red, creating a blood moon.

[00:01:41]Lunar eclipses [music] can be seen from the entire night side of Earth.

[00:01:49]Solar eclipses [music] are a rarer sight, with people traveling across the world to witness them. But how can the moon perfectly cover the sun at all?

[00:02:01]Although the sun is about 400 times larger than the moon, it's also [music] roughly 400 times farther away.

[00:02:10]This makes them appear the same size in the sky, allowing the moon to perfectly [music] cover the sun.

[00:02:18]There are three types of solar eclipse: a partial eclipse, when the moon covers only part [music] of the sun, and annular eclipse, when the moon is farther from the Earth, leaving a bright ring of light, also [music] called the ring of fire.

[00:02:34]And the most spectacular of all, the total solar eclipse.

[00:02:41]Totality can last [music] anywhere from a few seconds to a few minutes.

[00:02:47]It's only visible along a narrow path called the path of totality. [music] The track of the moon's shadow across Earth.

[00:02:56]Totality can only be seen from within the moon's full shadow, called the umbra.

[00:03:02]From the partial shadow, called the penumbra, we can see a partial eclipse.

[00:03:08]The path of totality is incredibly narrow.

[00:03:12]Even though total solar eclipses happen anywhere on Earth about every 18 months, it can take centuries before one returns to the [music] same place, which is why witnessing totality is so extraordinary.

[00:03:28]Little by little, the world begins to change.

[00:03:33]Trees project tiny crescent suns onto the ground, and shadows grow sharper.

[00:03:40]The temperature drops, and the colors of the sunset appear across the horizon.

[00:03:46]The moon covers more of the sun until only a thin string of lights is revealed. These are called Baily's beads, shaped by the moon's valleys.

[00:03:58]Then, a flash of light, the diamond ring, and suddenly, a total solar eclipse.

[00:04:07]For a few minutes, day turns [music] into night.

[00:04:11]Birds stop chirping and return to their nests. Night creatures begin to stir.

[00:04:18]It's daytime, but we're able to see bright planets and stars.

[00:04:23]Look up, and you'll see the sun's outer [music] atmosphere, the wispy, glowing corona.

[00:04:30]For most of human history, total solar eclipses were the only way we could observe it. Today, >> [music] >> we've found ways to extend this moment.

[00:04:40]Missions from the European Space Agency can recreate eclipse-like conditions in space, allowing us to study the corona beyond the few minutes of totality.

[00:04:51]Since 1995, ESA and NASA's Solar and Heliospheric Observatory, or SOHO, has used an instrument called a coronagraph, which revealed massive solar eruptions, and uncovered thousands of comets flying close to the sun.

[00:05:09]Proba 3 uses two spacecraft flying in precise formation so that one blocks the sun [music] for the other, creating an artificial eclipse that allows scientists to observe the inner corona for hours at a time.

[00:05:25]Meanwhile, Solar Orbiter studies the sun from closer distances.

[00:05:31]It has provided some of the first close-up views of the sun's polar regions, and is helping scientists understand the origin of the solar wind.

[00:05:43]Earth observation satellites in space can capture the moon shadow as it races across Earth.

[00:05:50]Today, scientists can predict eclipses with extraordinary precision, mapping their paths centuries into the future and [music] into the past, which is how we know that on May 28, 585 BC, a total solar eclipse likely brought a truce between rival nations. And just as the Lydians and the Medes froze more than two millennia ago, we still stop everything [music] to look up.

[00:06:22]Because eclipses bridge together the past and the present. [music] They connect legend to science.

[00:06:31]They remind us that even in moments of darkness, there is always something to discover.

[00:06:38]From ancient myths to modern science, we've come to understand eclipses [music] like never before.

[00:06:46]And still, when the sky goes dark during the middle of the day, it feels like magic.