Sıcaklık gün boyunca değişkendir.

The temperature is variable throughout the day.

Breakdown of Sıcaklık gün boyunca değişkendir.

• olmak: to be
• gün: the day
• boyunca: throughout
• değişken: variable
• sıcaklık: the temperature

Questions & Answers about Sıcaklık gün boyunca değişkendir.

What case is gün in here, and how does boyunca work?

Boyunca is a postposition meaning “throughout” or “during.” It follows a noun in the nominative case, so gün stays unchanged. Together gün boyunca literally means “during the day” or “throughout the day.”

What is the function of the -dir in değişkendir?

-dir is the third-person singular copula suffix. It:

• Turns the adjective değişken (“variable”) into a full predicate (“is variable”).
• Adds a tone of general truth or formality.
  In casual speech you can drop it (e.g. değişken), but in written/factual statements -dir is normally kept.

Why not use the verb değişiyor (“is changing”) instead of değişkendir?

Because they express different ideas:

• Değişiyor (present continuous of değişmek) means “it is changing right now.”
• Değişken-dir states a general property: “it is variable.”

Can I omit -dir and just say Sıcaklık gün boyunca değişken?

Yes. In spoken or informal Turkish you often hear the copula dropped:
“Sıcaklık gün boyunca değişken.”
However, in written or more formal styles you include -dir to signal definiteness and register.

Is gün boyu the same as gün boyunca?

Practically, yes: both mean “throughout the day.” Differences are subtle:

• gün boyunca is a noun + postposition.
• gün boyu is a compound phrase (literally “day long”).
  They’re largely interchangeable in everyday speech.

Can I swap the word order and say Gün boyunca sıcaklık değişkendir?

Absolutely. Turkish has flexible word order. Starting with Gün boyunca simply shifts emphasis to the time frame. The sentence remains correct and equally clear.

Why is there no article before sıcaklık (“temperature”)?

Turkish has no definite (“the”) or indefinite (“a/an”) articles. A bare noun like sıcaklık can mean “temperature” in general or “the temperature,” depending on context.

How would I express this in the past tense, e.g. “Yesterday the temperature was variable throughout the day”?

Add dün (“yesterday”) and change -dir to the past copula -di:
“Sıcaklık dün gün boyunca değişkendi.”
You could also say dün bütün gün değişkendi or dün gün boyu değişkendi for slight stylistic variation.