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An important capability of the BETA search was rapid and automatic re-observation of candidate signals , achieved by observing the sky with two adjacent beams , one slightly to the east and the other slightly to the west. A successful candidate signal would first transit the east beam , and then the west beam and do so with a speed consistent with Earth 's sidereal rotation rate .
 Earth
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: media, plant, vehicle, astronomical object, time, disease, animal, location, person, organization, mythical figure, food, biology, geographical phenomenon, instrument, event 
Text: {0} 
Answer:
 Earth