Tenmon hakase observed the celestial bodies and reported in fortune-telling, which was sealed if there was any unusual event (it's called tenmon misso), and also taught the students the way of fortune-telling through astronomical observation.
天文博士の職掌は、天体を観察し異変があればその吉凶を占って密封して奏聞する（これを天文密奏という）こと、及び天文生に天体を観察し吉凶を占う方法を教えることだった。