Learn Turkish: İyi ki güneş yakar diye koruyucu krem getirdin. - Good thing you brought sunscreen in case the sun burns us.

Using the aorist (the "general" tense, seen here in yakar) immediately before diye expresses taking a precaution against a likely possibility. It literally translates to "thinking 'the sun burns'", but it functions to mean "in case the sun burns." This is a standard structure for expressing why a precaution was taken.

The lesson mentions we can also use the conditional. Could we say güneş yakarsa diye instead?

Yes, absolutely! Both güneş yakar diye (aorist) and güneş yakarsa diye (conditional) mean "just in case the sun burns." The aorist version feels a bit more like anticipating a natural, expected outcome (the sun naturally burns people), while the conditional focuses slightly more on the hypothetical "if it happens" aspect. In everyday speech, they are virtually interchangeable.

I usually see "sunscreen" translated as güneş kremi. Is koruyucu krem common?

Güneş kremi is indeed the most standard everyday term. Koruyucu krem literally means "protective cream." The speaker is just being slightly more descriptive here, and because the word güneş (sun) was already used in the first clause (güneş yakar diye), using koruyucu krem nicely avoids repeating the word.

Why isn't there an accusative ending on koruyucu krem (like koruyucu kremi)?