On the nature of things (books 4 - 6)   

Where the year's node renders the shades of night
Equal unto the periods of light.
For when the sun is midway on his course
Between the blasts of north wind and of south,
Heaven keeps his two goals parted equally,
By virtue of the fixed position old
Of the whole starry Zodiac, through which
That sun, in winding onward, takes a year,
Illumining the sky and all the lands
With oblique light- as men declare to us
Who by their diagrams have charted well
Those regions of the sky which be adorned
With the arranged signs of Zodiac.
Or else, because in certain parts the air
Under the lands is denser, the tremulous
Bright beams of fire do waver tardily,
Nor easily can penetrate that air
Nor yet emerge unto their rising-place:
For this it is that nights in winter time
Do linger long, ere comes the many-rayed
Round Badge of the day. Or else because, as said,
In alternating seasons of the year
Fires, now more quick, and now more slow, are wont
To stream together- the fires which make the sun
To rise in some one spot- therefore it is
That those men seem to speak the truth who hold
A new sun is with each new daybreak born.

The moon she possibly doth shine because
Strook by the rays of sun, and day by day
May turn unto our gaze her light, the more
She doth recede from orb of sun, until,
Facing him opposite across the world,
She hath with full effulgence gleamed abroad,
And, at her rising as she soars above,
Hath there observed his setting; thence likewise
She needs must hide, as 'twere, her light behind
By slow degrees, the nearer now she glides,
Along the circle of the Zodiac,
From her far place toward fires of yonder sun-
As those men hold who feign the moon to be
Just like a ball and to pursue a course
Betwixt the sun and earth. There is, again,
Some reason to suppose that moon may roll
With light her very own, and thus display
The varied shapes of her resplendence there.
For near her is, percase, another body,
Invisible, because devoid of light,
Borne on and gliding all along with her,
Which in three modes may block and blot her disk.
Again, she may revolve upon herself,
Like to a ball's sphere- if perchance that be-
One half of her dyed o'er with glowing light,
And by the revolution of that sphere
She may beget for us her varying shapes,
Until she turns that fiery part of her
Full to the sight and open eyes of men;
Thence by slow stages round and back she whirls,
Withdrawing thus the luminiferous part
Of her sphered mass and ball, as, verily,
The Babylonian doctrine of Chaldees,
Refuting the art of Greek astrologers,
Labours, in opposition, to prove sure-
As if, forsooth, the thing for which each fights,