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The basic requirement for passive solar heating is that the solar collectors must face the prevailing sunlight ( south in the Northern Hemisphere , north in the Southern Hemisphere ) , and the building must incorporate thermal mass to keep it warm in the night .
 Northern Hemisphere, Southern Hemisphere
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Northern Hemisphere, Southern Hemisphere