Former constellations are constellation

Constellation

In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....

s that are no longer recognized by the International Astronomical Union

International Astronomical Union

The International Astronomical Union IAU is a collection of professional astronomers, at the Ph.D. level and beyond, active in professional research and education in astronomy...

 for various reasons. Many of these constellations existed for long periods of time, even centuries in many cases, which means they still have a large historical value and can be found on older star charts.
Argo Navis

Argo Navis

Argo Navis was a large constellation in the southern sky that has since been divided into three constellations. It represented the Argo, the ship used by Jason and the Argonauts in Greek mythology...

 is the only constellation from Ptolemy

Ptolemy

Claudius Ptolemy , was a Roman citizen of Egypt who wrote in Greek. He was a mathematician, astronomer, geographer, astrologer, and poet of a single epigram in the Greek Anthology. He lived in Egypt under Roman rule, and is believed to have been born in the town of Ptolemais Hermiou in the...

's original list of 48 constellations that is no longer officially recognized.