The brightest star of Argo is Canopus, called Suhaïl by Al-Sufi. It is the second brightest star in the heavens; but it is not visible in northern latitudes. The Harvard photometric measures make it nearly one magnitude brighter than the zero magnitude, about two magnitudes brighter than Aldebaran, and about half the brightness of Sirius. This fine star has been suspected of variable light. Webb says, "It was thought (1861) in Chili brighter than Sirius." Observing it in the Punjab, the present writer found it on several occasions but little inferior to Sirius, although very low on the southern horizon. From recent observations by Mr. H. C. McKay in Australia, he believes that it is variable to the extent of at least half a magnitude.[440] But it is difficult to establish variations of light in very bright stars. The parallax of Canopus is _very_ small, so its distance from the earth is very great, and it must be a sun of gigantic size. According to Al-Fargani, Canopus was called the star of St. Catherine by the Christian pilgrims in the tenth century.[441] It was called Suhaïl by the old Arabians, a name apparently derived from the root _sahl_, "a plain"; and Schjellerup suggests that the name was probably applied to this and some other southern stars because they seem to move along a plain near the southern horizon. Al-Sufi says that he measured the latitude of Schiraz in Persia, where he observed, and found it to be 29° 36'; and hence for that place Canopus, when on the meridian, had an altitude of about 9°. Canopus was the ancient name of Aboukir in Egypt, and is said to have derived its name from the pilot of Menelaus, whose name was Kanobus, and who died there from the bite of a snake. The star is supposed to have been named after him, and it was worshipped by the ancient Egyptians. Al-Sufi does not mention the famous variable star η Argûs, which, owing to the precession of the equinoxes, he might possibly have seen _close to the horizon_, if it had been a bright star in his day. It lies between φ Velorum and α Crucis. Both of these stars are mentioned by Al-Sufi, but he says nothing of any bright star (or indeed any star) between them. This negative evidence tends to show that η Argûs was not visible to the naked eye in Al-Sufi's time. This extraordinary star has in modern times varied through all degrees of brightness from Sirius down to the 8th magnitude! Schönfeld thought that a regular period is very improbable. It seems to be a sort of connecting link between the long period variables and the _novæ_ or temporary stars. It is reddish in colour, and the spectrum of its light is very similar to that of the temporary stars. Whether it will ever become a brilliant object again, time alone can tell; but from the fact that it was presumably faint in Al-Sufi's time, and afterwards increased to the brightness of Sirius, it seems possible that its light may again revive.