ペガスス座五十一番星、太陽に似たる黄色き恒星なり。其のスペクトル型はG2.5IVにして（或る資料に依ればG4-5Vあり）、年齢七十五至八十五億歳と推測せらる、太陽（四十六億歳）より年老る可能性高し。其の質量は太陽に比して四%余り大きく、太陽に比して重元素成分富む。表面温度は太陽と同じやや低き程度なりが、輝きに於いては三十%余り上回り。是れはペガスス座五十一番星が太陽に比して大なる宇宙体なることを意味す。是ゆえに、ペガスス座五十一番星を準巨星に分類せしめるカタログあり。
ペガスス座五十一番星、其の近接せる軌道を持つ惑星有ること知られたり。此の如き惑星有れば、恒星の活動活発となり易き旨指摘あるも、スペクトルやX線の測定に依れば、今般のペガスス座五十一番星の活動は極めて低調にして、まさにマウンダー極小期の如くの状態に在りと示されん
Observations and Analysis of the 51st Star of Pegasus
51st star in the constellation Pegasus is a yellowish star similar to the Sun. Its spectral type is G2.5IV (G4-5V according to some data), and its age is estimated to be 75 to 85 billion years old, likely older than the Sun (46 billion years old). Its mass is about 4% greater than that of the sun, and it is richer in heavy elements than the sun. Its surface temperature is slightly lower than that of the sun, but its luminosity is about 30% higher. This means that the 51st star of Pegasus is a larger cosmic body than the sun. For this reason, there is a catalog that classifies 51 Pegasus as a quasi-giant star.
It is known that there are planets with orbits close to 51 Pegasus. It has been pointed out that the presence of such a planet would easily lead to increased stellar activity, but according to spectral and X-ray measurements, the activity of 51 Pegasus is extremely sluggish at this time, just as it is during the Maunder Minimum.