The moon, Earth’s closest celestial neighbor, has been an object of wonder and mystery since time immemorial.

Scientific missions over the centuries have peeled away layers of that mystery, but the moon continues to harbor many secrets. This timeline of humanity’s exploration of the moon, provided by NASA, is not by any means comprehensive but does highlight some of the major milestones dating back four centuries:

Galileo Galilei made the first telescopic observation of the moon. (Image credit: NASA)

1609: Hans Lippershey invented the telescope.