magnitude at maximum also varies greatly. At times it vies with stars of the second magnitude, and often it only attains a brilliance of the fifth magnitude. At minimum it is generally of the ninth magnitude, only a thousandth part of its greatest brilliance, and one twentieth as bright as the faintest stars visible to the naked eye.
Mira is of a deep red colour and gives an interesting spectrum. Espin points out a similarity between the spectrum of Mira and the celebrated Nova Aurigæ. Herschel notes an observation of Omicron Ceti on the 6th of November, 1779, when this wonderful star equalled Aldebaran in brightness.
The amateur astronomer with a telescope of 3″ aperture or better can observe very well all the changes in light that take place in this remarkable star. Change seems to bespeak life, and hence the observance of variable stars must ever prove a source of fascination and wonder to those who make a study of them, for they, of all the seeming lifeless orbs that gaze so steadfastly on the centuries, exhibit inherent qualities that distinguish them in the firmament as man is distinguished on earth.
For three centuries this star has been under observation and as yet shows no sign of relaxation. No satisfactory theory has yet been found to account for all the variations in the light of these long-period variables. It has been suggested that the irregularities are caused by the phases of some general law, like the law of the maxima and minima of sun spot activity.
τ Ceti is one of our nearest neighbours in space, its distance being estimated as nine light years.
