Here is the passage, the first four lines of the poem at the beginning of Book II, part III, p. 185 in Loeb Classical LIbrary version.
Cum polo Phoebus roseis quadrigis
lucem spargere coeperit,
pallet albentes hebetata vultus
flammis stella prementibus.
(My translation, as literal as I can make it.)
When in-the-sky Phoebus with his rosy chariot
the-light to-scatter begins,
the star dimmed grows pale
by-flames oppressing the whitening looks.
Here is my reasoning for the last two lines, which I find difficult.
pallet: “grows pale”, predicate of subject stella
albentes: accusative plural, modifies vultus, “whitening looks”
vultus: “looks”, accusative plural, direct object of prementibus
hebetata: perfect passive participle, modifies stella
flammis: ablative plural, ablative of cause or manner
prementibus: ablative plural, present active participle, modifies flammis
I’d say ablative absolute for prementibus flammis, but otherwise, looks fine - the prose would be something like flammis prementibus albentes vultus, hebetata stella pallet (because the sun’s flames were outshining the whitening faces, the star dimmed).
You might find this version of the poem useful–it includes Latin paraphrases, notes, etc. I don’t know about you, but I love working with Latin in Latin.
Ubi primum Sol rubeo curru quadrijugo vectus incepit diffundere diem per coelum, nocturna sidera retusa ignibus instantibus Solis, contracto candore, pallent.
Literally // Verbatim
“When in the sky Phoebus from his rosy chariot
daylight to strew has begun,
pales its bright appearances the weakened
star on account of [L&S: palleo + dative] the suppressing flames”