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Continuing our hiatus on grammar topics, this lesson will be about basic astronomy terminology. Our solar system and the cosmos are great topics to have with speakers as many of us have been fascinated with the stars since we were kids. 

With that having being said, it must be noted that this lesson will focus on astronomy (天文学・アストロノミー) as opposed to astrology (占星術・アストロジー). East Asian culture adds its unique flare to astrology, and so it would be remiss of us to lump that field together with this discussion on astronomy. 

Our solar system is known in Japanese as 太陽系. Quite literally, it is the '太陽 System.' At its center is the Sun. Its Latin scientific name in Japanese contexts is ソル (Sol), but in everyday speech, it is referred to as either 太陽 (the Sino-Japanese word) or 日・陽 (the native word). 

Orbiting the Sun are eight planets along with the dwarf planet Pluto. Our Earth is planet three and has its own satellite known as the Moon in English but 月 in Japanese. Colloquially, the Sun and Moon are often respectively called お日様 and お月様. Some speakers may switch out ～様 for ～さん.

Our own planet Earth is known as 地球, but you may occasionally here アース used figuratively. The names of the planets are summarized in the chart below.

After you're comfortable with the names of the planets, you're now ready to tackle all the other astronomy terms that there is to talk about. As for what you'll be studying here, we'll be focusing only on those that might come up in conversation. 

Relating to Planets　惑星関連の用語

1. 彗星 is both the technical word for “comet” and the most frequently used word for it in everyday speech. As for, 箒星, it is treated as a poetic expression just like the English phrase "shooting star." 

2. The term for "eclipse" by itself is 蝕・食. The latter is the simplified spelling. 
3. Colloquially, 大気 suffices as the word for atmosphere, but 大気圏 encompasses all parts of the atmosphere up to the boundary between the outer edge and space itself whereas 大気 typically refers just to the part of the atmosphere that we view as air.

Relating to Stars　恒星関連の用語

1. 恒星 is the astronomical term for a “star” whereas 星 is the common day word. Another difference is that 星 may refer to any celestial body, including the Earth and other planets.
2. "The Heavens," although not a true astronomical word, is 天（国）. 

Regarding Research into the Universe 宇宙研究関連の用語

While providing context for many of the words introduced above, the examples below also provide additional terminology with the aid of beneficial contexts.

9. 水星は、太陽に最も近く公転している惑星だ。
Mercury is the planet that revolves closest to the Sun.

10. 巨大な隕石が地球に衝突する可能性は何パーセントですか。
What percentage is the possibility that a large meteorite will collide with Earth?

11. オゾン層が破壊されると、地球に届く紫外線の量が増えてしまう。

If the ozone layer is destroyed, the amount of ultra-violet rays that reach Earth will increase.

12. ほぼ全員の宇宙飛行士がなんらかの宇宙酔いを経験します。
Almost all of the astronauts experience some amount of space adaptation syndrome.

13. ブラックホールとは高密度大質量の天体で、物質だけでなく光さえも吸い込んでしまうほど強力な重力を持っている。
A blackhole is a celestial body with high density and great mass that holds such strong gravity that it not only swallows matter but even light.  

14. 僕はひとり車で流星群を見に行きました。
I went by myself via car to go see a meteor shower.

15. 天王星の自転軸が横倒しになっている。
The axle of Uranus is on its side.

16. みんなで皆既月食を観察しましょう。
Let’s all observe a total lunar eclipse together.

Word Note: The antonym of 皆既月食 is 皆既日食.

17. 望遠鏡を覗き込んで、ほうき星を探した。
I looked into a telescope and searched for shooting stars.

18. 夜空を見上げたら、天の川が見えました。
I looked up at the night sky and could see the Milky Way.

19. 宇宙船に乗のる夢を見ました。
I dreamed of riding in a spaceship.

20. イオには、18個の活火山があります。
There are eighteen active volcanoes on Io.

21. エウロパの地下に海があるかもしれない。
There may be a sea below the surface of Europa.

22. 月の裏側には、隕石衝突でクレーターがボコボコと開いている。
On the backside of the moon, there are craters everywhere due to meteorite impacts.

23. 天文台で星を観たいです。
I want to see stars at an observatory.

24. 宇宙は膨脹し続つづけている。
The universe continues to expand.

25. 宇宙人が存在する確率が高いなら地球に来ないのは何故だろうか。
Why is it that if the probability that extraterrestrials is so high yet they haven’t come to Earth?

26. 火星は過去にフォボスとデイモスのほかにも小さい衛星がいくつかあったとされています。
It is said that Mars in the past had several other small satellites like Phobos and Deimos.

27. 天体を見るのに適した場所はどこですか。
Where is a suitable place to see celestial bodies?

28. 小惑星帯は原始の太陽系の名残りに見えるが、原始の状態を保っているわけではない。
The asteroid belt may look like relics of the primal solar system, but it is not the case that it maintains a primal condition.

29. 国際宇宙ステーションとは、アメリカ合衆国、ロシア、日本、カナダ及び欧州宇宙機関 (ESA) が協力して運用している宇宙ステーションである。
The International Space Station is a space station which is operated in collaboration of the United States, Russia, Japan, Canada and the European Space Agency (ESA).

30. 宇宙塵は地球に降り注ぐ宇宙の塵である。
Space dust is dust from space that falls to Earth.

31. 大気圏とは、地球を取り巻く薄い大気の層のことである。
The atmosphere is the thin stratum of air that surrounds Earth.

32. なぜ惑星は公転の軌道から外れないのか。
Why is it that planets don’t leave their revolution orbits?

33. ビッグバンとは、宇宙の開闢直後に宇宙の膨張が始まった時点を指します。
The Big Bang marks the point in time when universe expansion began right after the creation of the universe.

34. 冥王星は準惑星の典型例である。
Pluto is a classic example of a dwarf planet.