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  • Still confused as to whether the Moon is a star or a planet?

  • I can fix that.

  • Hey guys, Amy here to talk space on DNews.

  • There has been a lot of talk recently about dwarf planets vs. “regularplanets, comets,

  • asteroidsnot to mention some questions what what exactly a natural satellite is.

  • Well, let's break down what exactly is kicking around in our Solar System.

  • At the centre is our Sun, which is a star.

  • A star is a luminous ball of gas, mostly hydrogen and helium, that is held together by its own gravity

  • Nuclear fusion in its core produces photons, the light particles we see, as well as heat and trace amounts of other heavy elements.

  • But not all stars are the same.

  • Stars can be different colours depending on their temperature, hotter stars looking slightly

  • bluer while cooler stars look slightly more red.

  • And stars are typically different sizes, the cooler stars being smaller.

  • As stars evolve and age, depending on their mass, they expand and eventually puff up as

  • red giants and rip themselves to shreds (that's what happens to stars about the mass of our Sun)

  • and turn into a white dwarf or, if they are really massive, they explode as supernovas

  • before turning into neutron stars or black holes.

  • Then there are brown dwarfs, which are sometimes called failed stars because they just aren't

  • big enough to start the fusion reaction that makes a star bright.

  • Brown dwarfs also have planet-like qualities, making them a kind of bridge between stars and planets.

  • Orbiting all kinds of stars are the planets, but for a body to be classified as a planet

  • it has to meet three additional criteria laid out by the International Astronomical Union:

  • It has to be large enough to be round, it cannot be a satellite of another body,

  • and it must have cleared its orbit of all nearby debris.

  • This all basically puts a minimum size limit on planets, but as long and they're big

  • enough planets can come in different types and sizes.

  • Earth is a rocky, terrestrial planet, as are Mercury, Venus, and Mars.

  • The outer planets Jupiter, Saturn, Uranus, and Neptune, are called gas giants, though those last two are sometimes called ice giants as well.

  • When we talk about planets around other stars, we have slightly different descriptors.

  • There are super Earths, which aren't exactly what they sound like.

  • These are planets more massive than Earth but still far less massive than Uranus or

  • Neptune, which are 15 and 17 times as massive as the Earth respectively.

  • On the other end of the size spectrum are dwarf planets, planets that are too small

  • to have cleared their orbital path of debris, like Ceres, the dwarf planet we've talked about before, in the asteroid belt.

  • Pluto is a dwarf planet as well, though in recognition of everyone's favourite little body,

  • the IAU recently designated all dwarf planets that orbit beyond Neptune as plutoids.

  • But regardless of size, type, or distance from its host star, any planet can have a moon.

  • A moon is a natural satellite, a body that makes an orbit around a planet.

  • Moons can have water like Europa, can have thick atmospheres like Titan, or be, for all

  • intents and purposes, a dead world like our own Moon.

  • As long as it's orbiting a planet, it's a moon.

  • Of course, there are more subcategories and intricacies in individual bodies, but those are sort of the basics.

  • Does that clear things up?

  • If you have any more questions on celestial bodies, let us know in the comments below or you can ask me on Twitter as @astVintageSpace.

  • And don't forget to subscribe for more DNews every day of the week.

Still confused as to whether the Moon is a star or a planet?

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B2 中上級

月は星なのか? (Is The Moon A Star?)

  • 195 11
    Jerry Liu に公開 2021 年 01 月 14 日
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