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The point at which an object is farthest away from the center of mass of the star it is orbiting.
[ap(o)- + Greek astron, star (probably on the model of aphelion); see ster- in Indo-European roots.]
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.