9173
Assuming a circular orbit , annual aberration causes stars exactly on the ecliptic ( the plane of Earth 's orbit ) to appear to move back and forth along a straight line , varying by on either side of their position in the Sun 's frame .
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Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
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