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The total solar eclipse to be observed on June 22nd next year.
Literal
Next year June 22 [target-に] observe-passive-attributive total-solar-eclipse.
A headline-style verbless phrase — the entire thing is a noun phrase, with 観測される ('will be observed,' passive attributive) modifying 皆既日食 ('total solar eclipse'). Common in news headlines and captions, which often omit predicates entirely. 皆既 ('total,' contrasting with 部分 'partial') is the specific meteorological term for a total eclipse.