一等星(いっとうせい)

Compound of 一等(いっとう) ('first class; first rank') and 星(せい) ('star'). The magnitude classification originated with the ancient Greek astronomer Hipparchus and is now part of the standard Japanese elementary-school and middle-school science curriculum.

Usage

• Typically used in everyday speech, educational materials, and popular astronomy. Professional astronomers use precise decimal magnitudes instead.
• Worldwide there are about 21 stars classified as 一等星(いっとうせい). Well-known examples include シリウス (Sirius), ベガ (Vega), アルタイル (Altair), アンタレス (Antares), and ベテルギウス (Betelgeuse).
• Smaller numbers (first class) indicate brighter stars; larger numbers (sixth class) indicate the faintest stars visible to the naked eye.

Common collocations

• 一等星(いっとうせい)が輝(かがや)く: a first-magnitude star shines
• 一等星(いっとうせい)を見(み)つける: to spot a first-magnitude star
• 一等星(いっとうせい)クラス: first-magnitude class (rare)
• 冬(ふゆ)の大三角(だいさんかく): the Winter Triangle — formed by three first-magnitude stars

Related words

• 二等星(にとうせい): second-magnitude star — the next category down.
• 六等星(ろくとうせい): sixth-magnitude star — the faintest category visible to the naked eye.
• 等級(とうきゅう): magnitude (astronomical) — the general technical term.
• 恒星(こうせい): fixed star — the general astronomical term for a star, as opposed to a planet.