“That wonderful tell-tale, the ‘telescope,’ reveals the double
character of some stars,” said Mr. Marple. “There are six thousand
stars which are thus double.
That is singular.
There are some in the Pleiades, in the Dog, in Orion, and in the
Southern Cross and Crown. But the most wonderful part of my story is
yet to come. Some of these double stars revolve round each other.
What! Great suns at a tremendous distance from one another, walk
round one another? Why, if they have planets round them, like our sun
has, these must have a fine double journey to make. How many of these
strange stars are there?
About 650 of them are Binary or revolving.
But which stands still to have the other revolving round it?
They both move, each one round the other.
A regular polka in the heavens, father. And yet I suppose they are not
just like a gentleman and his lady partner.
I don’t know that; for it has been observed that a number have
different colours to their companions. While one is blue, the other
will be yellow. One shall be green, and its mate will be orange.
One-half are white, and one-tenth are both blue.
That does please me. How I should like to be in a planet where my sun
should be blue, and its companion sun red. It would be so funny to
get up in the morning and see my sun blue, throwing a blue tint on
everything. Then, when the other sun rose, a rich red would steal over
the blue, and change everything. But when the blue sun had set, the
red one would have it all its own way, and bathe my world in its ruddy
light.
That fancy is good, and not very improbable either; especially if the
other sun should come pretty near your sun at times, as it is likely
they move in an ellipse.
Can you tell me, dear father, how long these pleasant binary stars take
in performing their polka?
One in Hercules takes thirty-one years. In our old Great Bear, a
binary pair take sixty-one, and in Leo eighty-two. In the Swan we have
178 years, and in the Virgin 182. In the Crown we have two several
times given of 608 and 736 years. It is believed that one pair are
1200 years. The North Polar Star is double, and is thought by some to
revolve in 6000 years.
Please, father, tell me some more about the colours of the double folk.
The Polar double stars are red and white. In Scorpion, there is a white
one and a lilac one; in the Centaur, we have both orange; in Andromeda,
crimson and green; in the Lion, gold and green; in one of Scorpio,
White and plum; in Castor, yellow and green; in Antares, both are
bright red; Arcturus was all red in 1841, and yellow in 1852.