skyline vs apparent horizon

skyline and apparent horizon both are nouns.

Word	Noun	Adjective	Verb	Adverb
skyline	Yes	No	No	No
apparent horizon	Yes	No	No	No

As nouns, skyline and apparent horizon are synonyms defined as:

skyline and apparent horizon: the line at which the sky and Earth appear to meet

Other synonyms of skyline include horizon, sensible horizon, visible horizon.

skyline (noun)	apparent horizon (noun)
the line at which the sky and Earth appear to meet	the line at which the sky and Earth appear to meet
the outline of objects seen against the sky