PERSON@1 estimated the diameter at NUMBER@1 miles -LRB- NUMBER@2 km -RRB- , but since he also gave NUMBER@3 miles -LRB- NUMBER@4 km -RRB- as the diameter of PERSON@2 , he was clearly overestimating the albedo ; using the modern figure for PERSON@2 gives Themis a diameter of NUMBER@5 km .

PERSON@1 thought that the diameter of Themis was about NUMBER@1 miles -LRB- NUMBER@2 km -RRB- . PERSON@1 had also discovered the moon PERSON@2 , but modern astronomers know that PERSON@1 made a mistake when he gave NUMBER@3 miles -LRB- NUMBER@4 km -RRB- as the diameter of PERSON@2 .
