yo Sidereal Astronomy. [January, 
mixture of a red evening, and a night becoming shorter and 
shorter, until the blue sun came back to opposition, as it 
was situated at the commencement of this description. 
In most of these systems of double stars, the little star 
turns round the larger, not in a circle, but describing an 
elongated ellipse. The stability of the system demands that 
this little star should not approach too near to the larger 
one, because, in this case, supposing, as is most likely, that 
the planets circulate in the same plane as the stars them- 
selves, these planets might be attracted by the central sun 
at the moment of the perihelion passage, and abandon their 
primitive sun, to the great detriment of their inhabitants, 
who would doubtless be burnt up before the astronomers of 
these worlds had been able to definitely prove the desertion. 
It is indispensable that these systems be very well restrained 
round each of the two suns, and that the obedient gravi- 
tating planets be kept close under the protecting wing of 
their own special sun. But in all cases there must be on 
them the most singular alternation of seasons. 
Thus in all planetary systems governed by a double sun, 
our double alternation of day and night is replaced by a 
quadruple alternation ; i, a double day lighted by two suns 
at a time ; 2, a single day lighted by a single sun ; 3, 
another single day lighted by the other sun ; 4, finally some 
hours of complete night, when the two suns are together 
below the horizon. 
And the splendour of these natural illuminations can 
hardly be conceived by our terrestial imagination. The 
tints which we here admire in these stars can only give a 
distant idea of the real value of their colours. Already in 
passing from our misty latitudes to the clear regions of the 
tropics, the colours of the stars deepen, and the heavens 
become a veritable casket of precious stones. What would 
this be if we were transported beyond the limits of our 
atmosphere ? Seen from the moon, these colours should 
appear splendid. Antares, a Herculis, Pollux, Aldebaran, 
Betelgeuse, Mars, shining like rubies ; the pole star, 
Capella, Castor, ArCturus, Procyon, would be celestial 
topazes, whilst Sirius, Vega, and Altair would shine like 
diamonds, eclipsing all by their dazzling whiteness. What, 
above all, would this be if we could get near enough to them 
to distinguish their luminous discs, instead of seeing only 
brilliant points divested of all diameter. 
Blue days, violet days, red days, green days ! For us to 
form an idea of these strange effects, let us mentally change 
for an instant the colour of our sun, and suppose that 
