How to Decide If Solar System Should Be Capitalized
You should capitalize “Solar System” when you’re talking about Earth’s specific planetary system, especially in formal, scientific, or educational contexts. If you’re mentioning other planetary systems, keep it lowercase.
Make sure to be consistent—don’t mix uppercase and lowercase in the same sentence. Style guides like APA and Chicago agree on this rule.
Understanding when to capitalize depends on whether you’re treating it as a proper noun or a general term. Keep this in mind, and you’ll see how context shapes usage.