O céu está brilhante hoje.

In European Portuguese, most singular, countable nouns are preceded by a definite article—even when we speak about general or universal concepts like “the sky.” So instead of saying just céu, we say o céu.
• O indicates a specific noun (here, “the sky”)
• English often drops the article with abstract or generic items, but Portuguese usually keeps it

Portuguese has two verbs for “to be”: ser and estar.
• Estar describes temporary states or conditions (e.g. the sky’s current appearance)
• Ser describes permanent or defining characteristics (e.g. “O céu é azul” in a general sense)
Since brightness can change day by day, we choose está brilhante.

The digraph lh represents the palatal lateral consonant /ʎ/. It’s somewhat like the “lli” in the English word “million,” but more pronounced:
• bri–ʎan–te
• Place your tongue against the roof of your mouth, letting air flow around the sides

1. Position: Most Portuguese adjectives follow the noun. Saying “céu brilhante” is the standard order.
2. Agreement: brilhante ends in -e, so it’s invariant for gender (masculine/feminine) and only pluralizes:
   – Singular: brilhante
   – Plural: brilhantes

Yes. Portuguese allows some flexibility for emphasis:
• Hoje o céu está brilhante. (Emphasizes today)
• O céu está brilhante hoje. (Neutral order)
Both are perfectly correct; you choose based on what you want to highlight.