Em agosto, nós passamos a jantar mais tarde porque o dia parece mais longo.

Portuguese normally uses em before months to mean in:

• em agosto = in August
• em janeiro = in January
• em dezembro = in December

So Em agosto is the normal way to say In August.

In Portuguese, months and days of the week are normally not capitalized:

• agosto
• segunda-feira
• sábado

That is different from English, where August is capitalized.

Not really. Portuguese often leaves out subject pronouns because the verb ending already shows the subject. Passamos already tells you the subject is we.

So both of these are natural:

• Nós passamos a jantar mais tarde.
• Passamos a jantar mais tarde.

Including nós can add emphasis, contrast, or extra clarity.

Here it is present indicative, used for a current or habitual situation. The idea is that, in August, we start / we now have dinner later.

This is especially important in European Portuguese spelling, because the simple past form is usually written passámos. So:

• passamos = present
• passámos = simple past

The structure passar a + infinitive means to begin to, to start to, or to come to do something.

So passamos a jantar mais tarde does not mean we pass dinner later. It means something like:

• we start having dinner later
• we begin to have dinner later
• we come to have dinner later

It often suggests a change from an earlier habit.

Because passar in this meaning uses the pattern passar a + infinitive. The a is part of the grammar of the expression.

Similar patterns are common in Portuguese:

• começar a estudar = to start studying
• aprender a cozinhar = to learn to cook
• passar a jantar mais tarde = to start having dinner later

So a is not optional here.

Here, jantar is a verb in the infinitive, meaning to have dinner or to dine.

Portuguese often uses the same form for the infinitive verb and the noun:

• jantar = to have dinner (verb)
• o jantar = dinner (noun)

In passamos a jantar, it is clearly the verb because it comes after a in the structure passar a + infinitive.

Portuguese usually forms comparatives with mais + adjective/adverb:

• mais tarde = later
• mais longo = longer
• mais cedo = earlier
• mais alto = taller / higher

English often has special -er forms, but Portuguese normally uses mais instead.

Because porque as one word usually means because and introduces a reason or explanation:

• Jantamos mais tarde porque o dia parece mais longo.

The other forms are different:

• por que = why / for what reason or for which
• porquê = the reason
• por quê = typically used at the end of a question

So in this sentence, porque is the correct form.

Portuguese uses the definite article more often than English. So o dia is the natural way to say the day here.

Saying just dia parece mais longo would sound incomplete in normal Portuguese. The article makes the phrase grammatical and natural.

Parece means seems or appears, so it expresses an impression. The sentence is saying that the day feels longer.

• o dia parece mais longo = the day seems longer
• o dia é mais longo = the day is longer

Using parece makes the statement softer and more subjective, which fits this context well.

Because longo agrees with dia, and dia is masculine singular.

So:

• o dia longo
• a noite longa

Since the noun is o dia, the adjective must be masculine too: mais longo.

Yes, and it would be understood. But there is a slight difference in nuance.

• começar a + infinitive focuses on beginning an action
• passar a + infinitive often suggests a change of habit or situation from that point on

So passamos a jantar mais tarde is especially good if you want to suggest that dinner used to be earlier, and now it has become later.