To illustrate what I have said, we will speak about another system of
shooting stars; they are due every August, from the 9th to the 11th,
and their directions diverge from a point in the constellation of
Perseus. I may remind you of the dates of the recurrence of this shower
as well as of the November meteors of which we have just spoken, by
quoting the following production:--
If you November’s stars would see,
About the fourteenth watching be.
In August, too, stars shine through heaven,
On nights between nine and eleven.
It may be worth your while to remember these lines, and always to keep
a look-out on the days named. The August meteors, the Perseids we
often call them, do not make gorgeous displays, in particular years,
with the regularity of the Leonids. There have been, no doubt, some
exceptionally grand showers between the 9th and the 11th of August, but
we cannot predict when the next splendid one is due. There are vast
numbers of stragglers all round the track of the Perseids. In fact,
it would seem as if the great race had gone on for such a long period
that the cluster had to a great extent broken up, and that a large
proportion of the meteors were now scattered the whole way around the
course with tolerable uniformity. This being so, it follows that every
time we cross the track we are nearly certain to fall in with a few of
the stragglers, though we may never enjoy the tremendous spectacle of a
plunge through a dense host of meteoroids.
There are many other showers besides the two I have mentioned. Some
shooting stars are to be seen almost every fine night, and those
astronomers who pay particular attention to this subject are able
to make out scores of small showers which might not interest you.
Each of these is fully defined by the night of the year on which it
occurs and the position of the point in the heavens from which the
meteors radiate. Of these I must mention one. It is not usually very
attractive, but it has a particular interest, as I shall now explain.
On the 27th of November, 1872, a beautiful meteoric shower took place.
You will notice that though the month is the same, the day is entirely
different from that on which the Leonids appear. This shower of the
27th is called the Andromedes, because the lines of direction of the
shooting stars of which it is composed seem to diverge from a point in
the constellation Andromeda. Ordinarily speaking, there is no special
display of meteors connected with the annual return of this day; but in
1872 astronomers were astonished by an exhibition of shooting stars
belonging to this system. They were not at all bright when compared
with the Leonid meteors. They were, however, sufficiently numerous to
arrest the attention of very many, even among those who do not usually
pay much attention to the heavens.
The chief interest of the shower of Andromedes centers in a remarkable
discovery connecting meteors and comets. There is a comet which was
discovered by the astronomer Biela. It is a small object, requiring a
telescope to show it. This comet completes each revolution in a period
of about seven years; or rather, I should say, that was the time which
the comet used to spend on its journey, for a life of trouble and
disaster seems of late to have nearly extinguished the unfortunate
object. In 1872 the comet was due in our neighborhood, and on the
night of the 27th of November, in the same year, the earth crossed the
track, and, in doing so, the shower of shooting stars was seen. This
was a remarkable coincidence. We crossed the path of the comet at the
time when we knew the comet ought to be there; and though we did not
then see the comet, we saw a shower of shooting stars, and a wonderful
shower too. A circumstance so peculiar suggested at once that the comet
and the shooting stars must in some way or other be connected together.
This is a suggestion we can test in another manner. We know the history
of the comet, and we are aware that at the very time of the shower,
the comet was approaching from the direction of the constellation of
Andromeda. It was coming, in fact, from the very quarter whence the
shooting stars have themselves travelled. Taking all these things
together, it seems impossible to doubt that the shoal of shooting stars
was, if not actually the comet itself, something closely connected with
that famous body.