Questions & Answers about В воскресенье этот магазин не работает.
Here в is used in a time expression meaning on, and воскресенье is in the accusative.
The tricky part is that воскресенье is an inanimate neuter singular noun, so its accusative form looks the same as its nominative form. That is why you do not see any change.
Compare:
- в среду = on Wednesday
- в пятницу = on Friday
- в воскресенье = on Sunday
So the case is changing, but with воскресенье the form just happens to stay the same.
In Russian, days of the week are normally written with lowercase letters.
So:
- понедельник
- вторник
- воскресенье
This is different from English, where Sunday and Monday are capitalized. In Russian, you only capitalize them if they begin a sentence or are part of a title.