At the beginning of act 3, scene 2 in Shakespeare's Romeo and Juliet, Juliet is waiting for Romeo to come to her so they can spend their first night together as husband and wife. Juliet has sent the Nurse to get a rope ladder so Romeo can secretly climb up to Juliet's room later that evening.
Juliet is unaware of what has just occurred in the streets of Padua. Her cousin, Tybalt, has killed Mercutio, Romeo killed Tybalt, and the Prince has exiled Romeo for killing Tybalt.
PRINCE: And for that offence
Immediately we do exile him hence . . . [3.1.192–193]
Juliet is alone in the Capulet's orchard, doing her best to pass the time until nightfall.
JULIET: Gallop apace, you fiery-footed steeds,
Towards Phoebus’ lodging! Such a wagoner
As Phaeton would whip you to the west
And bring in cloudy night immediately. [3.2.1–4]
Juliet desperately wants the day to end as soon as possible so she can be with Romeo, and she makes reference to the sun moving across the sky.
In Greek mythology, Phoebus (also known as Helios and Apollo) is the god of the sun who drove the flaming chariot across the sky every day, making the sun rise and set. The "fiery-footed steeds" are the horses who pulled the chariot across the sky, and "Phoebus' lodging" is where the sun went to rest at night after it had made its journey across the sky.
Phaeton is Phoebus's son, who asked his father if he could drive the chariot of the sun through the sky for just one day, and Phoebus agreed to let him do so.
Juliet calling on Phaeton to whip the horses and drive the sun across the sky seems appropriate to the moment, but Phaeton's ride across the sky in his father's sun chariot had an unhappy ending.
Phaeton couldn't control the "fiery-footed steeds," and the chariot fell from the sky, scorching the Earth (and causing the Sahara desert) and nearly destroying the Earth's plants and crops. Zeus threw a thunderbolt at the chariot to stop it from crashing to Earth, and Phaeton fell into the river Eridanus.
Shakespeare probably knew the Phaeton story and uses it here as a subtle bit of irony and foreshadowing.
Juliet likely didn't know the entire Phaeton story, or, if she did, she chose to ignore the unhappy ending, much as she ignored the possibility that her relationship with Romeo was equally as ill-advised as Phaeton's chariot ride across the sky.
Nevertheless, these opening lines and the rest of Juliet's soliloquy demonstrate her utter joy and happiness at being married to Romeo, her excitement and anticipation of their night together, her ability to explore every possible image, allusion, and metaphor of day, night, sun, stars, and Romeo, and her impatience with the "tedious" passing of the day into night—as impatient as a "child that hath new robes and may not wear them." [3.2.31–32]
JULIET: O, here comes my nurse,
And she brings news; and every tongue that speaks
But Romeo's name speaks heavenly eloquence. [3.2.32–34]
It is ironic that the last person other than Juliet who we heard speak Romeo's name was the Prince, who banished Romeo from Padua under pain of death.
PRINCE: Let Romeo hence in haste,
Else, when he is found, that hour is his last. [3.1.200–201]