Can you remember all 9 planets? Or was it 8 planets? Oh, that’s right! Pluto isn’t a planet anymore. Doh! 

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Solar System Vocabulary

宇宙uchuuthe universe
天の川銀河amanogawa gingaThe Milky Way
太陽系tayoukeiThe Solar System
他の太陽系hoka no taiyoukeisolar system
太陽taiyouThe Sun
準惑星junwakuseidwarf planet
二酸化炭素nisankatansocarbon dioxide
tsukiThe Moon
酸化鉄sankatetsuiron oxide
ガスジャイアントgasu jaiantogas giant
土星の環dosei no warings of Saturn
天王星型惑星tennousei gata wakuseiice giant

太陽系 (Taiyoukei)

Today is a special lesson for all of you science and space fanatics out there. We’re going to explore the Solar System in Japanese and learn some pretty cool vocabulary in the process!  

English: The Solar System

Somewhere within the universe (宇宙, uchuu), there is a galaxy (銀河, ginga) called The Milky Way (天の川銀河, amanogawa ginga). In this Milky Way, there are many stars (星, hoshi) and their solar systems (他の太陽系, hoka no tayoukei). Our solar system is composed of a sun (太陽, taiyou), eight planets (惑星, wakusei), and smaller objects such as dwarf planets (準惑星, junwakusei), moons (衛星, eisei), asteroids (小惑星, shouwakusei), and comets (彗星, suisei).

太陽 (Taiyou)

English: The Sun

The sun is the center of our universe. It provides Earth with light and warmth and is essential for life to exist. It is composed mostly of hydrogen (水素, suiso) and helium (ヘリウム, heriumu). 

水星 (Suisei)

English: Mercury

Mercury (水星, suisei) is the smallest of the eight planets in our solar system. It is also the closest to the sun. You may also think that it’s the hottest planet, but that’s not the case. Mercury has no atmosphere (大気, taiki) to keep heat in and can get as cold as -280℉ at night!

水星 (Suisei)
水星 (Suisei)

In English, Mercury is named after the Roman messenger god Mercury. However, you may notice that the kanji for Mercury in Japanese is 水 (mizu), which means “water.” This is because the Japanese planet names are based off of an ancient Chinese conceptual system called the Five Elements—or the wuxing. The five elements that make up all life and existence are water (水), metal (金, kane), fire (火, hi), wood (木, ki), and earth (土, tsuchi). Since all of the planets work together in harmony to affect life on Earth, they have been labeled as each of the five elements. Mercury has been labeled “water.”

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金星 (Kinsei)

English: Venus

Venus (金星, kinsei) is the second planet from the sun and is the brightest, most visible planet from Earth. Perhaps this is why astronomers named it the “gold planet.” Venus is made of mostly carbon dioxide (二酸化炭素, nisankatanso), is close in size and proximity to Earth, and is by far the hottest planet in the solar system with a mean surface temperature of 863℉.

地球 (Chikyuu)

English: Earth

Here it is! The home to all life in the universe—or at least all life that we know of! Earth is the perfect distance from the sun to sustain life and has oxygen (酸素, sanso) in the atmosphere, which is what we need to breathe!    

月 (Tsuki)

English: The Moon

It may not be a planet, but it’s our closest cosmic neighbor. Some say it’s made of cheese, but you and I know better.

火星 (Kasei)

English: Mars

The next planet from the sun is our fiery red neighbor Mars (火星, kasei). Its reddish appearance is caused by a prevalence of surface iron oxide  (酸化鉄, sankatetsu). Due to the gradually expanding sun, we may be living on this planet in the next billion years or so! 

木星 (Mokusei)

English: Jupiter

The granddaddy of them all! This is the largest planet in the solar system, and, rather than having a solid surface that you can walk on like Earth or Mars, Jupiter is composed of gas and is known as a gas giant (ガスジャイアント, gasu jaianto).

土星 (Dosei)

English: Saturn

The second-largest planet is also arguably the most beautiful. Saturn is known for its golden appearance and rings (土星の環, dosei no wa) made of ice and rocks.

天王星 (Tennousei)

English: Uranus

You may notice that the Japanese name for Uranus no longer follows the wuxing Five Elements. This is because the planets Uranus and beyond are not visible by the naked eye from Earth. Therefore, the Japanese name was translated from the English planet naming system. 天王 (tennou) means “king of the heavens,” in reference to the Greek god Uranus.

Uranus (as well as Neptune) is an ice giant (天王星型惑星, tennousei gata wakusei), and, at a minimum temperature of -371℉, is the coldest planet in the solar system. 

海王星 (Kaiousei)

English: Neptune

Named after the Roman god of the sea, Neptune (海王星, kaiousei) is the farthest known planet from the sun. It gets its blue color from traces of methane (メタン, metan) on its outermost regions.    

冥王星 (Meiousei)

English: Pluto

Oh, what the hey. We can’t forget about Pluto! What could be the most unfortunate event in scientific history, in 2006 scientists re-defined the classification “planet,” and because Pluto wasn’t big enough, it was demoted to “dwarf planet” (準惑星, junwakusei). Now Pluto just kind of sits there out on the cold and lonely outskirts of the solar system. Don’t worry, Pluto! You still live on as a full-fledged planet in our hearts!

Below is a list of new Solar System vocabulary for you to use as a reference. We hope you enjoyed today’s lesson!

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