The Tail of the Swan

There's no doubt that Deneb represents the tail, not the head, of Cygnus, the Swan. The name Deneb itself is from the Arabic Dhanab, which means "tail."

Elsewhere in the heavens, we see a number of other stars with Deneb in their name: Denebola (tail of Leo, the Lion), Deneb Kaitos (tail of Cetus, the Whale), Deneb Algiedi (tail of Capricornus, the Sea-Goat)—and several stars whose Deneb-including names are rarely used. But Deneb is the Deneb—the most important star marking the tail of a constellation figure, the beautiful swan. Or at least that's the way things stand today: Deneb was known to the later medieval Arabs as dhanab al-dajaja—"the tail of the Hen." Most of us today much prefer to think of this lovely star as being the tail of a graceful swan.

There's certainly reason to compare the main pattern of Cygnus to the form of a swan. The line from Gamma Cygni to Eta Cygni and Beta Cygni, or just the line from Eta to Beta, is much longer than the line from Gamma to Deneb. This long line well represents a swan's long neck. Likewise, it represents the longer part of the upright beam of the "Northern Cross" aster-ism—the part before the transverse beam (in the imagining of the Swan, that transverse beam is the wings of the bird). And this means that Deneb marks the top of the imagined Northern Cross. Deneb can be a guide to many of the great sights in Cygnus (including nearby double stars 61 Cygni, Omicron-1 and -2 Cygni) and nebulae (including the North America Nebula, which may or may not be lit by Deneb).

No observer at midnorthern latitudes should fail to notice what happens to the orientation of the Northern Cross as it heads down toward the northwest horizon. The Northern Cross, when it reaches the horizon, at last stands upright—with Deneb the beacon shining at its top.

Although in the dark, natural skies of ancient times, Cygnus may have been almost overwhelmed by the Cygnus Milky Way, it's still surprising to me how little lore about Cygnus and Deneb seems to have come down to us. The

most famous swan in Greek mythology is, of course, the swan that Zeus Cygnus and turned into to ravish Leda. Deneb.

More than a thousand years ago, before they pictured a hen in the stars of Cygnus, the Arabs called Deneb by the title al-ridf. Paul Kunitzsch translates this as "the One Sitting Behind the Rider (on the same animal)" or just "the Follower." R. H. Allen translates it as meaning "the Hindmost." Kunitzsch notes that the title may be in reference to Deneb's relation to Delta, Gamma, Epsilon, and Zeta Cygni, which were called al-fawaris, "the Riders." The title al-ridf led to a later alternate name for Deneb that one still sometimes encounters: Arided.

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