mes.

Some stars accomplish their cycle of change in a few days, many in a few
weeks or months, and there are others which do not complete their
periods until the expiration of a number of years.

One of the most remarkable of variable stars is called Mira 'the
wonderful,' in the constellation Cetus. When at its maximum brilliancy
it shines for two or three weeks as a star of the second magnitude. It
then begins to gradually decline, and at the end of three months becomes
invisible. It remains invisible for five months, and then reappears, and
during the ensuing three months it regains by degrees its former
brilliancy. Mira completes a cycle of its changes in 334 days, and,
during that time, oscillates between a star of the second and tenth
magnitude. The variability of Mira Ceti was first observed by David
Fabricius in the sixteenth century.

Another remarkable star is Eta Argus, which is surrounded by the great
nebula in the constellation Argo Navis. It is invisible to the naked
eye, but in the telescope it has a reddish appearance, and is slightly
brighter than the stars in its vicinity. It was first observed by Halley
in 1677, and it was then of the fourth magnitude. In 1751 it had risen
to the second magnitude, and maintained its position as a star of this
class until 1837, when, on December 16 of that year, its brilliancy
suddenly increased, and it equalled in a short time Alpha Centauri. It
reached its maximum in 1843, and then it was surpassed only by Sirius.
It maintained its brilliancy for about ten years. In 1858, it declined
to the second magnitude, in 1859 to the third, and, gradually
diminishing, it became invisible to the naked eye in 1868. It is now of
the seventh magnitude, and is again increasing, and may soon resume its
position among the other stars. It is believed to have a period of
seventy years, and in that time its light ebbs and flows between the
seventh and first magnitudes.

The most interesting variable star in the heavens is Algol (the demon),
in the constellation Perseus. Its light fluctuations can be observed
without the aid of a telescope, and it completes a cycle of its changes
in two or three days. For about two days and thirteen hours it is
conspicuously visible as a star of the second magnitude; it then begins
to decline, and in about four hours sinks to the dimensions of a
fourth-magnitude star; it remains in this condition for twenty minutes,
and then increases gradually until,