Japanese Space and Planet Words: Sun, Moon, Stars and Planets

Hoshi, uchū and the night sky

星 (hoshi) is the everyday word for star, and it is also the building block of many space words. In compounds it is read sei: 惑星 (wakusei), planet, is literally a wandering star, and 衛星 (eisei), a satellite, is a guarding star. 宇宙 (uchū) is space as a whole, the universe.

Japanese often describes a clear night sky with 星がきれい (hoshi ga kirei), the stars are beautiful, and 星空 (hoshizora), a starry sky, is a word you will see in song titles and tourism brochures for mountain areas and islands.

Amanogawa, the river of heaven, is the Milky Way as you see it in the sky, and it is at the heart of Tanabata, the star festival in July, when two stars separated by the river are said to meet. The Milky Way as a galaxy in science is 銀河系 (gingakei).

The four words to start with

These four words cover most everyday talk about the sky. Sun and space use on'yomi compounds, while moon and star are short native words.

Ohisama and otsukisama, with the respectful お and さま, are affectionate words used with children and in picture books. Chikyū, Earth, literally means earth ball, and it is also the normal word for globe.

The eight planets and the weekday trick

The planet names are where Japanese pays off. The five planets known since ancient times share their first kanji with the weekdays, so if you know the days of the week you already know half the solar system. The outer two planets were named much later: Uranus is the heaven king star and Neptune the sea king star, translations of the Greek and Roman gods.

The moon: phases and moon-viewing

The moon has a special place in Japanese culture. In autumn, many people enjoy 月見 (tsukimi), moon-viewing, with dumplings and pampas grass, and the full moon of mid-autumn is called 十五夜 (jūgoya). Instead of a man in the moon, Japanese tradition sees a rabbit pounding rice cakes, an image you will meet in picture books and seasonal sweets.

Mikazuki literally means the moon of the third day, from the old lunar calendar. Because the romantic story is so well known, some people smile or tease you a little when you say tsuki ga kirei desu ne. If you only mean the view, kyō no tsuki, kirei da ne, tonight's moon is pretty, sounds more like a comment on the sky.

Shooting stars, comets and eclipses

These words turn up in the news whenever there is something to see in the sky. Japanese TV and websites announce meteor showers and eclipses in advance, and in some places people gather in parks and on rooftops to watch.

Suisei for comet uses the kanji 彗, a broom, because a comet's tail looks like a broom sweeping the sky. It sounds identical to 水星, Mercury, so in conversation people rely on context or say Harē suisei, Halley's Comet, with the name.

Rockets, astronauts and space science

Here Japanese mixes native kanji words and loanwords freely. Rocket and black hole are katakana, while astronaut and satellite are kanji compounds that are easy to read once you know 宇宙 and 衛星. Uchiage also means an after-party held when a project or a performance is finished, so the meaning comes from context.

A night of stargazing

Stargazing is 星を見る (hoshi o miru) in casual talk and 天体観測 (tentai kansoku), astronomical observation, in a more formal or hobby sense. Many towns, mountain areas and islands promote their dark skies, and planetariums, プラネタリウム (puranetariumu), are a popular date and family outing in cities.

Learn the solar system with Mocchi

Start with /kanji 星 and Mocchi gives you the meaning, the readings hoshi and sei, and words such as wakusei and ryūsei. Then ask: Quiz me on the planets in Japanese, in random order. Mocchi notices which ones you hesitate over, perhaps tennōsei and kaiōsei, and folds them into your next review instead of starting from scratch.

Afterwards, make cards with /create-flashcards and fly them in Mocchi Flight: steer Mocchi through the gate with the right planet name.

Common learner mistakes

• Using uchū for space in a room. A free space or parking space is supēsu.
• Saying hoshi for planets. Hoshi works casually, but a planet is wakusei.
• Mixing up 水星 (Mercury) and 彗星 (comet). They sound the same; the kanji tell them apart.
• Reading 土星 as tosei. It is dosei.
• Saying tsuki ga kirei desu ne to someone you just met. The romantic meaning is well known, so expect a reaction.