TO KNOW THE STARRY HEAVENS 
J 55 
in other words that a configuration 
such as the big dipper would always 
remain a dipper of exactly the same 
shape. Bruno about 1600 seems to 
have been the first to question the cor- 
rectness of this view and to suggest 
that this might not be so. Halley in 
1718 was the first actually to prove that 
any of the so-called fixed stars move. 
Since then many have been found to 
move, and astronomers feel sure that 
all are moving. The motions of the stars 
in the big dipper are particularly in- 
teresting. In 1869 Proctor called at- 
tention to the very peculiar fact that 
now the big dipper after 50,000 years, 
the figure being that found by joining 
the points of the arrows in the upper 
figure. There is then no longer a close 
resemblance to a dipper, but then by 
that time the shape of dippers may also' 
have undergone changes. 
Other moving clusters have since 
been found until now there are about 
seven such groups known, including 
the Hyades and the Pleiades. None, 
however, seems as remarkable as the 
Ursa Major group. We have not fin- 
ished the story. A still further aston- 
ishing fact was pointed out by Hertz- 
five of the seven stars forming the dip- 
per moved slowly in parallel directions 
at the same rate. The other two moved 
in a direction nearly opposite, the mo- 
tions of these two being quite similar. 
The facts indicated pretty conclusively 
that the five stars constituted a system 
moving together through space under 
some common influence. The stars are 
so far apart that no one would have 
suspected any relationship between 
them. The stars at the end of the 
handle and the northernmost star 
of the two on the farther side of the 
bowl do not belong to the system. 
Figure 2 shows what is occurring. 
The dots show the present positions of 
the seven stars (1900). The arrows in- 
dicate the direction and amount of the 
star's motions in 50,000 years. The 
lower figure shows the shape of what is 
sprung in 1909 when he announced 
that there were eight more stars mov- 
ing in just the same direction as the 
five of the big dipper and therefore be- 
longing to the system. Other stars have 
since been added, Bottlinger in 1914 in- 
cluding seventeen in the group, with 
some others which may perhaps belong 
also. The star next to the end of the 
handle of the dipper (Mizar) is a 
double star and close beside it is the 
star Alcor, which belongs to the sys- 
tem, as does a faint star in the position 
marked D, making eight in all in Ursa 
Major. The other nine are scattered at 
E in Auriga, at F in Corona, at G in 
Serpens, faint ones at H in Bootes, at 
I in Virgo and at J in Eridanus on the 
western horizon, one in Cygnus not 
visible to the naked eye and not marked 
very close to the northern horizon, and 
