Learn French: Nous observons de vastes constellations.

This is the core rule for this lesson! Normally, the plural of un or une is des. However, when a plural adjective comes right before the noun (like vastes does here), des gets reduced to de. Because of this rule, we say de vastes constellations instead of des vastes constellations.

Why does the adjective vastes come before the noun here?

While most French adjectives go after the noun, a specific set of common adjectives goes before it. You might remember the acronym BAGS (Beauty, Age, Goodness, Size). Since vaste describes size and expansiveness, it naturally sits in front of the noun.

Do I pronounce the 's' at the end of vastes and constellations?

No, both are completely silent. In French, a final 's' is generally only pronounced if it links to a vowel sound in the following word (a liaison). Because constellations starts with a consonant, the 's' on vastes stays silent. The 's' on constellations is silent because it is at the end of the sentence.

Is observons a regular verb?