Deneb Algedi is Delta Capricorni, an eclipsing binary at about 39 light years whose components periodically pass in front of one another, dimming the pair slightly, and it is the brightest star of Capricornus. Its name, from the Arabic dhanab al-jady, means the tail of the goat, or of the sea-goat, the strange composite creature, half goat and half fish, that the constellation depicts, a figure going back to Mesopotamian tradition. It marks the fishy tail with which the climbing goat of the zodiac ends.
Deneb Algedi's eclipses are shallow, a partial rather than total blocking of one star's light by the other, similar in kind to Algol's though smaller in amplitude, and the system is close enough, at under forty light years, that its orbital and physical parameters are unusually well determined compared with most of the other eclipsing pairs named in this catalogue. Deneb Algedi's status as Capricornus's brightest star despite the faintness of the constellation as a whole reflects how dim the sea-goat figure is overall, one of the less conspicuous members of the zodiac to the naked eye. Its shallow, precisely timed eclipses have made Deneb Algedi a useful calibration target for photometric instruments being tested against a known, well-characterised variable.
Sources AstronomyAndrew Fraknoi, David Morrison, and Sidney C. Wolff (OpenStax) with The Arabs and the StarsPaul Kunitzsch