Mauna ___ Observatory

LOA

This Hawaiian volcano is known as the largest by volume and hosts a key site for studying Earth's atmosphere and space. Its name means "long" in Hawaiian.

This clue refers to the Mauna Loa Observatory, a well-known research station in Hawaii that monitors atmospheric conditions like carbon dioxide levels. The blank is filled with "LOA," the name of the volcano where the observatory is located. It’s a straightforward fill-in-the-blank with no wordplay—just a direct reference to a famous scientific site.