* Earth and Sun are proper nouns, referring to specific planets. Proper nouns are always capitalized.
* President is a title used before a specific person's name, making it a proper noun. For example: "President Biden" or "the President of the United States".
* Department is a common noun and is only capitalized when it's part of a formal name (e.g., Department of Education) or when it begins a sentence.
Let me know if you have any other grammar questions!