The stars in their courses / by Sir James Jeans.

  • Jeans, James, 1877-1946.
Date:
1939
Catalogue details

Licence: In copyright

Credit: The stars in their courses / by Sir James Jeans. Source: Wellcome Collection.

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    Region 8—Cetus From the sidereal time-table, we find that Region 8 is on the meridian about 6 p.m. in January, so that it can be well seen in the winter months soon after darkness sets in. Towards the end of August it crosses the meridian at 4 a.m.; in September at 2 a.m.; in October at midnight; in November at 10 p.m. and in December at 8 p.m. Primarily, then, it is a region for observation on autumn evenings. Although Cetus is said to be the largest constella¬ tion of all, it does not possess many bright stars. It contains two second-magnitude stars and nine of the third and fourth magnitudes. The variable star Omicron Ceti (p. 96), or Mira Ceti, lies in this constellation. The German astro¬ nomer Fabricius discovered its variability more than 300 years ago. Its light continually changes, with a period of about eleven months, and exhibits ex¬ traordinary fluctuations of brightness. From being a faint telescopic star of the ninth magnitude, Mira slowly brightens up to the eighth, seventh, sixth magnitude in succession, after which it becomes visible to the unaided eye and gradually ascends to the second magnitude. It reaches its brightest about four months after the rise commences, and after staying at its brightest for nearly a month, it begins to decline. Slowly its brightness wanes until, five months later, it is again the insignificant tele¬ scopic star of the ninth magnitude from which it started. It is justly called Mira Ceti, the wonder-star of Cetus, for the light that it yields when at its maximum is about 500 times that given when at its minimum. Observers will do well to notice a gigantic W,