Complex sentence: Some astronomers explain this by presence of small temperature fluctuations within planetary nebulae; others claim that the discrepancies are too large to be explained by temperature effects, and hypothesize the existence of cold knots containing very little hydrogen to explain the observations.
Split into simpler sentences: Some astronomers explain this by the presence of small temperature fluctuations within planetary nebulae. Others claim that the discrepancies are too large to be explained by temperature effects, and hypothesize the existence of cold knots containing very little hydrogen to explain the observations.