Translation guide
The English word "planet" refers to a large celestial body orbiting a star. In Japanese, the most common and direct equivalent is 惑星 (wakusei). However, traditional names for the classical planets (e.g., Mercury, Venus) use 星 (hoshi) or specific kanji compounds, and in casual contexts, 星 (hoshi) can mean "planet" as well as "star." This guide covers the main term, traditional names, and usage notes.
Referring to a planet as a celestial body, especially in scientific or general contexts.
The standard word for 'planet' in modern Japanese, used in astronomy, news, and everyday conversation.
地球は太陽系の惑星の一つです。
Earth is one of the planets in the solar system.
新しい惑星が発見された。
A new planet has been discovered.
Literally 'star,' but often used to mean 'planet' in casual speech, especially when referring to a specific planet or in set phrases. Context usually clarifies the meaning.
Can be ambiguous; use 惑星 when you need to be clear that you mean 'planet' and not 'star.'
あの明るい星は金星だよ。
That bright planet is Venus.
夜空にたくさんの星が見える。
You can see many stars (or planets) in the night sky.
Referring to the classical planets by their traditional Japanese names, which are often used in astrology, literature, or everyday talk about the visible planets.
Mercury. The kanji mean 'water star.'
水星は太陽に一番近い惑星です。
Mercury is the planet closest to the sun.
Venus. The kanji mean 'metal/gold star.' Often called 明けの明星 (あけのみょうじょう) 'morning star' or 宵の明星 (よいのみょうじょう) 'evening star.'
Earth. The kanji mean 'ground sphere.'
Mars. The kanji mean 'fire star.'
Jupiter. The kanji mean 'wood star.'
Saturn. The kanji mean 'earth/soil star.'
Referring to dwarf planets like Pluto or planets outside our solar system.
Dwarf planet. Used for bodies like Pluto, Eris, etc.
冥王星は準惑星に分類されています。
Pluto is classified as a dwarf planet.
惑星 (wakusei) specifically means 'planet,' while 星 (hoshi) is a broader term for any celestial body that appears as a point of light, including stars, planets, and sometimes even satellites. In everyday conversation, 星 is often used for planets when the context is clear, but in scientific or precise contexts, 惑星 is preferred.
The traditional Japanese names for the planets are based on the Chinese five elements (水, 金, 火, 木, 土) plus 天 and 海 for Uranus and Neptune. These are the standard names used in astronomy and daily life. Katakana versions (e.g., マーキュリー for Mercury) are also understood but less common except in some science fiction or foreign media contexts.
金星は「明けの明星」とも呼ばれます。
Venus is also called the 'morning star.'
Earth is the planet we live on.
There is a possibility that water existed on Mars.
木星は太陽系で最大の惑星です。
Jupiter is the largest planet in the solar system.
Saturn's rings can be seen with a telescope.
Uranus. The kanji mean 'sky king star.' Less commonly used in everyday speech; sometimes referred to by its katakana name ウラヌス.
天王星は横倒しに自転しています。
Uranus rotates on its side.
Neptune. The kanji mean 'sea king star.' Like Uranus, sometimes called ネプチューン in casual contexts.
海王星は太陽系の一番外側の惑星です。
Neptune is the outermost planet in the solar system.
Exoplanet (planet outside the solar system).
多くの系外惑星が発見されています。
Many exoplanets have been discovered.