Part 18

He has his foot on Fomalhaut, he leans back on Capricornus, and has Pisces, the Fishes, on the other side.

What is the great star north of Capricornus?

That is Altair, in Aquila the Eagle, whose wings are spread over the equator. Aquila is between Ophiuchus and Aquarius.

As we have got over Aquarius, and come to Pisces, which are over Cetus the Whale, I suppose we are at Aries again.

We are. But I should like you to know that Pegasus, the Flying Horse, is over Aquarius, and that the Swan and Lyre are between that and Hercules, and north of the Eagle. Taking a line from the south pole through the Whale’s tail, we have a bright star in the back of Pegasus, called Algenib, not far from the junction of the equator and ecliptic in Pisces.

The star beyond Algenib, further north, is larger, though.

Alpherat is its name, and it is one of the eyes of Andromeda, the lady with the chains on her hands.

O, I know all about that story, father. The ancients said she was fastened to a rock in the sea, and a monster was gnawing at her. But a warrior, called Perseus, came with his sword and delivered her.

Then, as you have Andromeda’s eye, you can fancy the Zodiacal Fish biting her, and Perseus with his sword to the left. There is a triangle between Aries and Andromeda.

What a dazzling star that is, forming the north corner of a triangle with Aldebaran and the Twins.

Yes, Capella, or the Little Kid, in the arms of Auriga, is certainly very fine. Auriga’s foot is on the Bull’s head. Half-way from Alpherat of Andromeda to Capella, is Medusa’s Head, just over the Pleiades.

We have gone round, I think, father, but I do wish I could see the old Bear again.

You have only to imagine yourself following out a line from the Belt through Castor and Pollux.

Yes, but I should have to dive down into the ocean to reach his claws.”

DOUBLE STARS.

“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.