Questions & Answers about Τη νύχτα κοιμάμαι στο σπίτι.
Because τη is the accusative form of the feminine definite article, while η is the nominative form.
Η νύχτα = the night (as the subject of a sentence)
- Example: Η νύχτα είναι κρύα. – The night is cold.
Τη νύχτα = the night in the accusative, here used as a time expression, meaning at night / during the night.
- Example: Τη νύχτα κοιμάμαι. – At night, I sleep.
In Greek, expressions of time like “in the morning”, “at night”, etc., often use the accusative without a preposition:
- το πρωί – in the morning
- το βράδυ – in the evening
- τη νύχτα – at night