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Page 59
[Page 210]
_Number._
We find about five thousand stars visible to the naked eye in the
whole heavens, both north and south. Of these twenty are of the
first magnitude, sixty-five of the second, two hundred of the third,
four hundred of the fourth, eleven hundred of the fifth, and three
thousand two hundred of the sixth. We think we can easily number
the stars; but train a six-inch telescope on a little section of the
Twins, where six faint stars are visible, and over three thousand
luminous points appear. The seventh magnitude has 13,000 stars;
the eighth, 40,000; the ninth, 142,000. There are 18,000,000 stars
in the zone called the Milky Way. When our eyes are not sensitive
enough to be affected by the light of far-off stars the tastimetre
feels their heat, and tells us the word of their Maker is true--"they
are innumerable."[*]
[Footnote *: _Telescopic Work._--Look at the Hyades and Pleiades
in Taurus. Notice the different colors of stars in them both. Find
the cluster Pr�sepe in Fig. 70, just a trifle above a point midway
between Procyon and Regulus. It is equally distant from Procyon and
a point a little below Pollux. Sweep along the Milky Way almost
anywhere, and observe the distribution of stars; in some places
perfect crowds, in others more sparsely scattered. Find with the
naked eye the rich cluster in Perseus. Draw a line from Algol to
a of Perseus (Fig. 67); turn at right angles to the right, at a
distance of once and four-tenths the first line a brightness will
be seen. The telescope reveals a gorgeous cluster.]
_Double and Multiple Stars._
If we look up during the summer months nearly overhead at the star
e Lyra, east of Vega (Fig. 72), we shall see with the naked eye
that the star appears a little [Page 211] elongated. Turn your
opera-glass upon it, and two stars appear. Turn a larger telescope
on this double star, and each of the components separate into two.
It is a double double star. We know that if two stars are near in
reality, and not simply apparently so by being in the same line of
sight, they must revolve around a common centre of gravity, or rush
to a common ruin. Eagerly we watch to see if they revolve. A few
years suffice to show them in actual revolution. Nay, the movement
of revolution has been decided before the companion star was
discovered. Sirius has long been known to have a proper motion, such
as it would have if another sun were revolving about it. Even the
direction of the unseen body could always be indicated. In February,
1862, Alvan Clark, artist, poet, and maker of telescopes (which
requires even greater genius than to be both poet and artist),
discovered the companion of Sirius just in its predicted place. As a
matter of fact, one of Mr. Clark's sons saw it first; but their fame
is one. The time of revolution of this pair is fifty years. But one
companion does not meet the conditions of the movements. Here must
also be one or more planets too small or dark to be seen. The double
star x in the Great Bear (see Fig. 70) makes a revolution in
fifty-eight years.
Procyon moves in an orbit which requires the presence of a companion
star, but it has as yet eluded our search. Castor is a double star;
but a third star or planet, as yet undiscovered, is required to
account for its perturbations. Men who discovered Neptune by the
perturbations of Uranus are capable of judging the cause of the
perturbations of suns. We have spoken of [Page 212] the whole orbit
of the earth being invisible from the stars. The nearest star in our
northern hemisphere, 61 Cygni, is a telescopic double star; the
constituent parts of it are forty-five times as far from each other
as the earth is from the sun, yet it takes a large telescope to show
any distance between the stars.[*]
[Footnote *: _Telescopic Work._--Only such work will be laid out
here as can be done by small telescopes of from two to four inch
object-glasses. The numbers in Fig. 75 correspond to those of the
table.
--------------------------------------------------------------------
| | | |Dist. of|Magni-| |
|No.| Name. | Fig. | Parts. |tudes.| Remarks. |
|---|------------|-------------|--------|------|---------------------|
| 1.| e Lyr� | 72 | 1' 56" | |Quadruple. |
| 2.| z Lyr� | 72 | 44 |5 & 6 |Topaz and green. |
| 3.| b Cygni | 73 | 34-1/2|3 & 6 |Yellow and blue. |
| 4.| 61 Cygni | 73 | 20 |5 & 6 |Nearest star but one.|
| 5.| Mizar | 67 | 14 |3 & 4 |Both white. |
| 6.| Polaris | 67 | 18-1/2|2 & 9 |Test object of eye |
| | | | | | and glass. |
| 7.| r Orionis |Frontispiece.| 7 |5 & 8 |Yellow and blue. |
| 8.| b Orionis | " | 9 |1 & 8 | Rigel. |
| 9.| d " | " | 10 |2 & 8 | Red and white. |
|10.| th " | " | | |Septuple. |
|11.| l " | " | 5 | |White and violet. |
|12.| s " | " A, B.| 11 |4 & 10|Octuple. |
|13.| Castor | 69 | 5-1/2|2 & 3 |White. |
|14.| Pollux | 69 | |Triple|Orange, gray, lilac. |
|15.| g Virginis | 70 | 5 |3 & 3 |Both yellow. |
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]
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