We use the with something that is single in the world:
The sky, the earth, the hell, the paradise, the sun…
We don’t use articles with breakfast, lunch, deener
Usually, we use a/an/the/me/… with a singular noun. a cat, a dog, a house.
We can’t use a singular countable noun without articles.
In English we always use the with:
— the names of the sea, the ocean: the Mediterranian sea, the Dnipro river, The Pacific ocean, the Atlantic ocean, the Amazone.