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Hipparchus described the constellation as containing fifteen stars , but the later astronomer Ptolemy ( 100 – 170 AD ) increased this number to thirty-one in his " Almagest " .
 person: Hipparchus; person: Ptolemy
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 person: Hipparchus; person: Ptolemy