Simplify the following text for a Grade 7 native English-speaking person.
Original: He was a prolific discoverer of asteroids , discovering 122 in all , from 136 Austria in 1874 to 1073 Gellivara in 1923 .
Simplified: He was a good finder of asteroids , finding 122 in all , from 136 Austria in 1874 to 1073 Gellivara in 1923 .