During a solar eclipse the sun (solar) is eclipsed by the moon (lunar). In other words, the moon eclipses the sun.
Three forms and three uses of the same word.
1) NOUN (eclipse)
In the phrase “solar eclipse” it is the name (noun) of an activity that can occur at any time. In this case it is the activity of obscuring or hiding from view.
2) VERB (eclipse)
a) ACTIVE VOICE (The 3rd person singular form of the verb “eclipse” used in the present tense):
In the clause “the moon eclipses the sun” the word eclipse tells what the moon does at the time that it happens.
b) PASSIVE VOICE (The past participle of the verb “eclipse” used to complete the passive voice of the verb eclipse in 3rd person singular of the present tense):
In the clause “the sun is eclipsed by the moon” the word eclipse tells what happens to the sun at the time that it happens.
Are you watching the eclipse now? Do not be eclipsed by the above grammar. It is simpler than you think, but more difficult than you believe.
And, let not the synonyms think and believe fool you into believing that they are very different in this context.
p.s. Solar is an adjective form of sun, and lunar is a adjective form of moon.