With its companion, it revolves round their common centre of gravity in five hundred and twenty years.

Their conjoint weight is about one-third that of the sun.
There is reason to believe that the great star Sirius, the brightest in the heavens, is about six times as far off as alpha Centauri.

His probable diameter is twelve million miles, and the light he emits two hundred times more brilliant than that of the sun.

Yet, even through the telescope, he has no measurable diameter; he looks merely like a very bright spark.
The stars, then, differ not merely in visible magnitude, but also in actual size.

As the spectroscope shows, they differ greatly in chemical and physical constitution.