Meteorology   

astronomical demonstrations are correct and the size of the sun is

greater than that of the earth and the distance of the stars from

the earth many times greater than that of the sun (just as the sun

is further from the earth than the moon), then the cone made by the

rays of the sun would terminate at no great distance from the earth,

and the shadow of the earth (what we call night) would not reach the

stars. On the contrary, the sun shines on all the stars and the

earth screens none of them.

(3) There is a third theory about the milky way. Some say that it is

a reflection of our sight to the sun, just as they say that the

comet is.

But this too is impossible. For if the eye and the mirror and the

whole of the object were severally at rest, then the same part of

the image would appear at the same point in the mirror. But if the

mirror and the object move, keeping the same distance from the eye

which is at rest, but at different rates of speed and so not always at

the same interval from one another, then it is impossible for the same

image always to appear in the same part of the mirror. Now the

constellations included in the circle of the milky way move; and so

does the sun, the object to which our sight is reflected; but we stand

still. And the distance of those two from us is constant and

uniform, but their distance from one another varies. For the Dolphin

sometimes rises at midnight, sometimes in the morning. But in each

case the same parts of the milky way are found near it. But if it were

a reflection and not a genuine affection of these this ought not to be

the case.

Again, we can see the milky way reflected at night in water and

similar mirrors. But under these circumstances it is impossible for

our sight to be reflected to the sun.

These considerations show that the milky way is not the path of

one of the planets, nor the light of imperceptible stars, nor a

reflection. And those are the chief theories handed down by others