THE GUIDE TO NATURE 
156 
moon. The distance of Venus from the 
sun does not change greatly, but its 
greatest distance from the earth is six 
times its least. For this reason the ap- 
parent size is ony a sixth as great. The 
facts are illustrated in Figure 2. 
In Position 1, when Venus is farthest 
from the earth, the face illuminated by 
the sun is turned toward the earth 
and Venus is “full,” as shown in the 
open circle. But being in nearly the 
same direction as the sun, we cannot 
see it, and. if we could, it would not be 
very bright, as it is far from us. At 2. 
being nearer, it looks larger, but we 
cannot see the whole disc, as the whole 
illuminated face is not turned towards 
the earth. Venus is then gibbouns — that 
is, more than half of the disc is visible. 
At 3, at elongation, Venus appears still 
larger, but only half of the illuminated 
side can be seen from the earth and 
Venus looks like the quarter moon. At 
4 the illuminated face of Venus is 
turned away from the earth and Venus 
is new. Near this position we see a 
very narrow crescent as shown, but 
Venus is then very close to us, so that 
this crescent is part of a very large disc 
and hence may be brighter than the 
full circle at 1. It happens that Venus 
is brightest between Positions 3 and 4. 
when its shape is that of the moon five 
days old. The proportion between the 
size of the crescent and the full circle at 
1 as drawn as accurate. When the moon 
appears in the Avest, it is a Avaxing 
moon, but Venus in the same position 
is Availing as to shape, but not necessa- 
rily in brightness. Comersely in the 
east in the morning. 
Mercurc- may be seen in the east be- 
fore sunrise the last feAA' days of the 
month. By passing opposition March 
4. Jupiter becomes an et'ening star, and 
will soon supplant Venus as the con- 
spicuous eA-ening star. Saturn similar- 
ly becomes an eA'ening star March 12. 
The earth is noAA' on the same side of 
the rings as the sun. and these may be 
seen as a narroAA’ needle of light extend- 
ing outAA’ard from the disc. 
The sun crosses the equator March 
20, 10:51 P. M. This marks the begin- 
ning of spring. 
It is announced that Slipher, of 
UoAvell Observatory, has found that a 
spiral nebula in Cetus is moving aAvay 
from us AA'ith the enormous Aelocity of 
1240 miles per second. It has been 
knoAvn for some time that spiral nebula 
move with great A'elocities (or else AA'e 
do), as great as 500 to 700 miles per 
second. This is the greatest A'elocity 
found anyAvhere. Why these enormous 
A'elocities exist in this class of bodies is 
still unexplained. 
jjl 5jc 3*C :«C :•£ 
Betelgeux. 
Last month AA'e mentioned the fact 
that the diameter of one of the stars, 
Betelgeux or Alpha Orionis, had been 
determined. It may be further ex- 
plained that the diameter of the sun, 
planet, etc., is determined by measur- 
ing the angle which its disc subtends. 
When this angle can be measured and 
the distance is knoAA'n it is easy to cal- 
culate the diameter in miles. The stars, 
hoAveA'er, are so far from us that the 
discs are too small to measure. When 
seen through a telescope stars shoAA- a 
spurious disc due to the diffraction of 
light the size of AA'hich decreases Avith 
larger telescopes. Unless the real disc 
AA'as larger than this its size could not 
be determined by ordinary means. 
Hence heretofore Ave haA'e been unable 
to actually determine the diameter of 
any star. It has been possible to cal- 
culate the diameter in some cases, such 
as in eclipsing binaries. Recently the 
diameters of some of the stars haA*e 
been predicted upon the basis of their 
spectrum and other characteristics. 
Both Eddington and Russell predicted 
the diameter of Betelgeux before the 
actual measurement AA'ith considerable 
accuracy. Both belieA-ed it to be a 
A ery large star, and this led to its selec- 
tion as a trial star. Other stars sug- 
gested as large by Russell are Antares, 
Aldebaran and Arcturus. All are red- 
dish stars. That Betelgeux is large is 
a confirmation of the theory' of eA r olu- 
tion of stars. AA'hich claims stars are red 
both near the beginning and end of 
their existence. For the development 
of this theory Russell has just been 
aAvarded the gold medal of the Royal 
Astronomical Society. Lack of space 
prevents a further discussion of this 
theory noAA'. 
A halo of beauty hovers 
Round everything that grOAvs, 
But is only fitted to it 
By one who sees and knoAA'S. 
— Emma Peirce. 
