Learn Hardcore Turkish: Bulut güneşi kaplıyor. - The cloud is covering the sun.

Because it’s a definite direct object. Turkish marks definite objects with the accusative suffix -(y)I, which harmonizes as -ı, -i, -u, or -ü. Since the last vowel of güneş is front (e), you get güneş + i → güneşi. It corresponds to “the sun,” not “a sun.”

Can I leave off the -i and say Bulut güneş kaplıyor?

Grammatically, a bare object can be indefinite in Turkish, but here it would sound odd because “a sun” is not natural. You normally keep the accusative: güneşi. Compare: Çocuk kitap okuyor (“The child is reading a book”)—here the bare object is fine because “a book” is indefinite and natural.

Why is the verb at the end?

Turkish default word order is Subject–Object–Verb, so Bulut (S) güneşi (O) kaplıyor (V) is normal. You can front elements for emphasis: Güneşi bulut kaplıyor (emphasizes that it’s the sun that’s being covered), or Bulut kaplıyor güneşi in speech for focus, but verb-final is the unmarked choice.

Where is the English word “is”? Why isn’t it written?

The “is … -ing” meaning is carried by the verbal suffix -yor. Turkish doesn’t use a separate “to be” here; kaplıyor already means “is covering.”

How is kaplıyor formed from the verb kaplamak (“to cover”)?

Take the stem kapla- and add the present continuous -(I)yor. Because the stem ends in a vowel, the final a/e of the stem drops/merges: kapla- + -ıyor → kaplıyor. The vowel in the suffix is ı (not i) due to vowel harmony with the back vowel a in the stem.

Why is it kaplıyor with dotless ı, not kapliyor with dotted i?

Vowel harmony: after a back vowel (a, ı, o, u), the high vowel in the suffix is back ı/u; after a front vowel (e, i, ö, ü), it’s front i/ü. Since kapla- has the back vowel a, the suffix uses -ıyor → -ıyor, realized as kaplıyor.

How do I pronounce the special letters here: ü, ş, and ı?

ü: a front rounded vowel (say “ee” while rounding your lips).
ş: like English “sh.”
ı (dotless i): a central/back unrounded vowel; approximate it with the vowel in English “roses” (the second syllable) or “sofa” (the a), but shorter.
So güneşi ≈ “gyu-NEH-shi” and kaplıyor ≈ “KAH-pluh-yor.”

Could güneşi mean “his/her sun”? Is there ambiguity?

Not here. In object position, “his/her sun” would be güneşini (possessive -i + accusative -i with buffer -n). Güneşi in this sentence is the accusative of “sun,” i.e., “the sun.” The possessive reading typically needs an explicit possessor or context and, as an object, shows up as -sini/-sını/-sunu/-sünü.

Can I drop the subject and just say Güneşi kaplıyor?

Yes—Turkish allows null subjects. Güneşi kaplıyor means “(It) is covering the sun,” with the subject understood from context (e.g., you’ve already been talking about the cloud).

If I say Bulutlar, should the verb be plural (kaplıyorlar)?

Both Bulutlar güneşi kaplıyor and Bulutlar güneşi kaplıyorlar are acceptable. Third-person plural agreement on the verb is optional; it’s more often used (and more expected) with human subjects. With non-human subjects like clouds, leaving the verb singular is very common.

Is kaplamak the only verb I can use? What about kapatmak or örtmek?

kaplamak: to cover/coat a surface extensively; natural for “a cloud covers the sun.”
kapatmak: to close/shut/block; Bulut güneşi kapatıyor highlights the blocking of light.
örtmek: to cover/veil; slightly more poetic: Bulut güneşi örtüyor.
All three can work; nuance differs.

How do I say “a cloud” vs “the cloud” as the subject?

Turkish has no articles. Use bir bulut for “a cloud” and context or demonstratives for definiteness: o bulut (“that cloud”) for a specific cloud. Plain bulut can be generic or context-dependent.

What’s the difference between kaplıyor and kaplar?

kaplıyor: present continuous—an action happening now or around now (“is covering”).
kaplar: aorist/habitual—general truths, routines, or tendencies (“covers [generally/usually]”).
So Bulut güneşi kaplar sounds like a general statement rather than a live description.

How do I put this in other tenses?

Past simple: Bulut güneşi kapladı (“covered”).
Past continuous: Bulut güneşi kaplıyordu (“was covering”).
Future: Bulut güneşi kaplayacak (“will cover”).
Reported/presumptive: Bulut güneşi kaplıyormuş (“apparently/is said to be covering”).