A mote it is to trouble the mind's eye.
In the most high and palmy state of Rome,
A little ere the mightiest Julius fell,
The graves stood tenantless and the sheeted dead
Did squeak and gibber in the Roman streets:
As stars with trains of fire and dews of blood,
Disasters in the sun; and the moist star
Upon whose influence Neptune's empire stands
Was sick almost to doomsday with eclipse:
And even the like precurse of fierce events,
As harbingers preceding still the fates
And prologue to the omen coming on,
Have heaven and earth together demonstrated
Unto our climatures and countrymen.
But soft, behold! lo, where it comes again!

Re-enter Ghost

I'll cross it, though it blast me. Stay, illusion!
If thou hast any sound, or use of voice,
Speak to me:
If there be any good thing to be done,
That may to thee do ease and grace to me,
Speak to me:
If thou art privy to thy country's fate,
Which, happily, foreknowing may avoid, O, speak!
Or if thou hast uphoarded in thy life
Extorted treasure in the womb of earth,
For which, they say, your spirits oft walk in death,
Speak of it: stay, and speak! 


Julius Caesar
Shakespeare's play about the conspirators who assassinate Julius Caesar can be reasonably assumed to have been first performed in 1599. The likelihood is that it appeared just before Hamlet, and so the references to ancient Rome discussed in this episode are hardly surprising since Rome was still on Shakespeare's mind. 

The Mote and the Beam
The parable of the mote and the beam is notable for having appeared in the gospels of both Matthew (7.1) and Luke (13.6), in key sermons given by Jesus to his followers. Its lesson is to be wary of criticising the faults of others before working on one's own issues. (A biblical version of the pot calling the kettle black, if you will.) 

Giordano Bruno
It's a little bit of a stretch to infer that Shakespeare is acknowledging that Earth's sun is a star in the reference to 'disasters of the sun' - since it was a very long time before science accepted the idea. Giordano Bruno was a Dominican friar who was also a philosopher, mathematician and astronomer, who posited the theory that we are not the centre of everything, and that there are conceivably multiple stars with planets in their orbits in the infinite universe. For these ideas (and for his rejection of several church doctrines) he was burned at the stake in Rome's Campo de' Fiori in 1600. He is considered an early martyr for science and free thought.