2 Dollars - Elizabeth II Eye of the Sahara: Space Day

The Eye of the Sahara — formally the Richat Structure — is a 40-kilometer-wide geological dome in Mauritania that spent decades puzzling researchers who initially assumed it was an impact crater. It isn't; erosion of a symmetrical anticline is the accepted explanation, though the debate ran well into the 1990s. Its fame in numismatic and collectibles markets stems almost entirely from its visibility from low Earth orbit, where it functions as a navigational landmark for astronauts. Niue's Space Day series exploited that association directly.