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  • - [Narrator] Our solar system is one

  • of over 500 known solar systems

  • in the entire Milky Way galaxy.

  • The solar system came into being

  • about 4.5 billion years ago, when a cloud

  • of interstellar gas and dust collapsed,

  • resulting in a solar nebula, a swirling disc

  • of material that collided to form the solar system.

  • The solar system is located

  • in the Milky Way's Orion star cluster.

  • Only 15% of stars in the galaxy host planetary systems,

  • and one of those stars is our own sun.

  • Revolving around the sun are eight planets.

  • The planets are divided into two categories,

  • based on their composition,

  • Terrestrial and Jovian.

  • Terrestrial planets including Mercury, Venus, Earth,

  • and Mars, are primarily made of rocky material.

  • Their surfaces are solid, they don't have ring systems,

  • they have very few or no moons,

  • and they are relatively small.

  • The smallest and closest to the sun is Mercury,

  • which has the shortest orbit in the solar system

  • at about three Earth months.

  • Venus is the hottest planet, with temperatures

  • of up to 867 degrees Fahrenheit, due to an atmosphere

  • of carbon dioxide and extensive lava flows.

  • Next to this world of fire is a world of water, Earth.

  • The water systems on this planet help create

  • the only known environment in the universe

  • capable of sustaining life.

  • The last of the terrestrial planets, Mars,

  • might have also supported life about 3.7 billion years ago,

  • when the planet had a watery surface, and moist atmosphere.

  • Beyond the four Terrestrial planets

  • of the inner solar system lie the Jovian planets

  • of the outer solar system.

  • The Jovian planets include gas giants Jupiter and Saturn

  • and ice giants Uranus and Neptune.

  • The gas giants are predominantly made of helium

  • and hydrogen, and the ice giants also contain rock, ice,

  • and a liquid mixture of water, methane, and ammonia.

  • All four Jovian planets have multiple moons,

  • sport ring systems, have no solid surface, and are immense.

  • The largest Jovian is also the largest planet

  • in the solar system, Jupiter.

  • Nearby is Saturn, the solar system's second largest planet.

  • Its signature rings are wide enough

  • to fit between Earth and the moon,

  • but are barely a kilometer thick.

  • Past Saturn are the ice giants, Uranus and Neptune.

  • The slightly bigger of these ice giants, Uranus,

  • is famous for rotating on its side.

  • Next to Uranus is Neptune, the outermost planet

  • in the solar system, and also one of the coldest.

  • Orbiting the Terrestrial planets is the asteroid belt,

  • a flat disc of rocky objects, full of remnants

  • from the solar system's formation.

  • From microscopic dust particles,

  • to the largest known object, the dwarf planet, Ceres.

  • Another disc of space debris lies much further out,

  • and orbits the Jovian planets, the icy Kuiper Belt.

  • Apart from asteroids, the Kuiper Belt is also home

  • to dwarf planets, such as Pluto,

  • and is the birthplace of many comets.

  • Beyond the Kuiper Belt is the Oort Cloud,

  • a vast, spherical collection of icy debris.

  • It is considered the edge of the solar system

  • since that is where the gravitational

  • and physical influences of the sun end.

  • Our solar system's particular configuration

  • of planets and other celestial objects,

  • all revolving around a life-giving star,

  • make it a special place to call home.

- [Narrator] Our solar system is one

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太陽系101|ナショナルジオグラフィック (Solar System 101 | National Geographic)

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    王杰 に公開 2021 年 01 月 14 日
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