Only "der blaue" changes in the accusative case to "den blauen" but not "die blaue" (singular), "die blauen" (plural) and "das blaue". For example: Er sieht die blaue Tasse, das blaue Buch und die blauen Blumen (plural).
The sky is the direct object.
He sees (nomative) the blue sky (Accusative)
Correct me if wrong
Why blauen ??? Not blau???
As I understand, the attibutive adjectives take the gender and the case of the noun they are describing.
Since here the sky is in accusative case - den Himmel, the adjective also gets accusative case - den blauen Himmel.
Himmel also means heaven. That answer should be accepted.
"blauen" implies "sky", though.
What if heaven is blue?
blue as in the German blue or the English blue? The German one sounds more fun :)
Slightly different concept could be written thus? He is looking at the blue sky. Er sieht den blauen Himmel an.
In American English there is an expression "blue heaven" (as in "my blue heaven").
"Heavens" should probably also work, too. Yes, "Himmeln" is plural to make heavens, but "heavens" can be used as the equivalent of "sky" in English. It's a more beautiful translation.
I thought when there is the indefinite article you are supposed to use the weak ending, which is always -e in singular?
That's the very question i came here to ask... I think that rule only applies in the nominative? Maybe someone could confirm?
Firstly the article is definite "Den", (showing masc and accusative); and secondly the adjective is weak accusative- with an "en" ending.
Why not, "He sees the blue skies." Too poetic?
I'm really struggling with colours.
Why is "watches" not accepted?
Because just as English uses different words for "sees" and "watches", so does Geman. I believe the German verb for "to watch" is "Anschauen".