"It is a special date."

Translation: Det er en speciel dato.

[eftermiddagen]

Why is it det and then en?

[RidderJakob]

It's 'det' until the gender of the noun has been established.

1. Det er en speciel dato

2. Hvorfor er DEN speciel?

2 uses 'den' because the gender is revealed :)

[Jnwulff]

No it does not matter what it is replacing. When saying that "it is (insert noun)" you always use "det"

Den 2/3, det er en dato

Solen, det er en stjerne (the sun, it is a star)

If you say "it is (insert adjective) you use "den" or "det" depending on what it is. That is the reason you use den in sentence number two (den er speciel) "speciel" is an adjective

Solen, den er stor (the sun, it is a big star)

If you, like here, have both an adjective and a noun you always use "det"