"Today is Sunday."
Translation:Dzisiaj jest niedziela.
I think I may have understood the difference between Dziś and Dzisiaj but I can't explain how or why
One is one syllable other is two. This is the only difference there is. We may prefer one or the other in a sentence for a stylistic reasons, but they are interchangeable.
Why isn't niedziela instrumental? Is it because it's a time period/day of the week?
Ah. I though dzisiaj was the subject. So a more accurate translation is something like "sunday is today"?
I am still confused by above few comments. If explanation is Niedziela is subject, then it seems to me, as well, that it should read "Niedziela jest dzisiaj". These replies to original question confused me.
In polish, adverbs usually precede verbs. Dzisiaj is an adverb in this sentence, so it comes before jest. This sentence describes WHEN Sunday is, rather than WHAT today is.
"Niedziela jest dzisiaj", as immery stated, would mean "Sunday is today" and be an answer to a "So... does anyone remember when's the next Sunday?" question. "Dzisiaj jest niedziela" answers "What day is today?" question.