1.
fixed star, star (astronomical)
A celestial body that generates its own light through nuclear fusion, as opposed to planets which reflect light. The sun is the nearest star to Earth.
太陽は恒星だ。
The sun is a star.
恒星は自ら光を放つ天体である。
A star is a celestial body that emits its own light.
夜空に見える光の大部分は、はるか遠くにある恒星からのものだ。
Most of the light visible in the night sky comes from stars that are extremely far away.
CONTRAST:
恒星 (star) vs. 惑星 (planet): Stars emit their own light; planets orbit stars and reflect light. In everyday Japanese, 星 covers both stars and planets in casual speech, while 恒星 is the precise scientific term.
ETYMOLOGY:
The characters 恒 (constant, permanent) + 星 (star) reflect the historical observation that stars appear fixed in position relative to planets, which visibly move across the sky.