On the nature of things (books 4 - 6)   

Going wherever their food invites and calls,
And feeding their flaming bodies everywhere
Throughout the sky. Yet which of these is cause
In this our world 'tis hard to say for sure;
But what can be throughout the universe,
In divers worlds on divers plan create,
This only do I show, and follow on
To assign unto the motions of the stars
Even several causes which 'tis possible
Exist throughout the universal All;
Of which yet one must be the cause even here
Which maketh motion for our constellations.
Yet to decide which one of them it be
Is not the least the business of a man
Advancing step by cautious step, as I.

Nor can the sun's wheel larger be by much
Nor its own blaze much less than either seems
Unto our senses. For from whatso spaces
Fires have the power on us to cast their beams
And blow their scorching exhalations forth
Against our members, those same distances
Take nothing by those intervals away
From bulk of flames; and to the sight the fire
Is nothing shrunken. Therefore, since the heat
And the outpoured light of skiey sun
Arrive our senses and caress our limbs,
Form too and bigness of the sun must look
Even here from earth just as they really be,
So that thou canst scarce nothing take or add.
And whether the journeying moon illuminate
The regions round with bastard beams, or throw
From off her proper body her own light,-
Whichever it be, she journeys with a form
Naught larger than the form doth seem to be
Which we with eyes of ours perceive. For all
The far removed objects of our gaze
Seem through much air confused in their look
Ere minished in their bigness. Wherefore, moon,
Since she presents bright look and clear-cut form,
May there on high by us on earth be seen
Just as she is with extreme bounds defined,
And just of the size. And lastly, whatso fires
Of ether thou from earth beholdest, these
Thou mayst consider as possibly of size
The least bit less, or larger by a hair
Than they appear- since whatso fires we view
Here in the lands of earth are seen to change
From time to time their size to less or more
Only the least, when more or less away,
So long as still they bicker clear, and still
Their glow's perceived.
Nor need there be for men
Astonishment that yonder sun so small
Can yet send forth so great a light as fills
Oceans and all the lands and sky aflood,
And with its fiery exhalations steeps
The world at large. For it may be, indeed,
That one vast-flowing well-spring of the whole
Wide world from here hath opened and out-gushed,
And shot its light abroad; because thuswise
The elements of fiery exhalations
From all the world around together come,
And thuswise flow into a bulk so big