No constellation begins with the letter Z. The International Astronomical Union recognizes 88 official constellations that cover the entire sky, and not a single one of them starts with this final letter of the alphabet. This gap stands out because the night sky holds patterns named for animals, heroes, tools, and mythical creatures, yet the letter Z is left empty among them.

The reason traces back to language and history. Most constellation names come from Latin, and many of those names trace even further back to ancient Greek myths and early Arabic star charts. The letter Z is rare at the start of words in Latin, so it almost never appears in the formal names astronomers settled on. When the International Astronomical Union fixed the official list in 1922 and drew firm borders for each region of the sky in 1930, the names already in common use carried forward. Letters like A, C, and S begin many constellations, while Z simply never entered the tradition.

A few names come close enough to interest curious stargazers. The bright star Zubenelgenubi sits in the constellation Libra, and its name begins with Z even though the constellation itself does not. Stars and other sky objects sometimes carry Z names drawn from older Arabic catalogs, but these are individual points of light rather than full constellations. If you are looking for the official patterns of the night sky, the letter Z marks the one corner of the alphabet that the constellations never reached.