Meine Schwester hat einen leichten Sonnenbrand auf der Nase.

In German, physical conditions are often expressed with haben (to have), not sein (to be).

So:

• Meine Schwester hat einen leichten Sonnenbrand. = My sister has a slight sunburn.

This is similar to English, which also says has a sunburn.

Meine Schwester is the subject of the sentence, so it is in the nominative case.

• Schwester is feminine
• the possessive word mein changes to meine in the feminine nominative singular

So:

• mein Bruder = my brother
• meine Schwester = my sister

Because this is the direct object of hat, it has to be in the accusative case.

Sonnenbrand is a masculine noun: der Sonnenbrand

Masculine accusative changes like this:

• der → einen
• adjective after einen gets -en

So:

• nominative: ein leichter Sonnenbrand
• accusative: einen leichten Sonnenbrand

That is why the sentence has:

• einen leichten Sonnenbrand

This is an adjective ending question.

In einen leichten Sonnenbrand:

• einen shows that the noun phrase is masculine accusative
• after that, the adjective takes the ending -en

So:

• ein leichter Sonnenbrand = a slight sunburn
• einen leichten Sonnenbrand = a slight sunburn (as direct object)

The ending is not random; it matches the grammar of the noun phrase.

Because this sentence describes a location, not movement.

The preposition auf can take:

• dative for location: on
• accusative for direction/movement onto

Here, the sunburn is located on the nose, so German uses the dative:

• auf der Nase = on the nose

Compare:

• Sie hat einen Sonnenbrand auf der Nase. = The sunburn is on the nose.
• Sie legt die Brille auf die Nase. = She puts the glasses onto the nose.

Because feminine nouns in the dative singular often use der.

So:

• nominative: die Nase
• accusative: die Nase
• dative: der Nase

Since auf here requires the dative, you get:

• auf der Nase

This is one of the very common article changes learners need to get used to.

German often uses the definite article with body parts when the owner is already obvious.

So instead of saying:

• on her nose

German very naturally says:

• auf der Nase = literally on the nose

Because the subject is my sister, it is already clear whose nose is meant.

English usually prefers a possessive:

• on her nose

German often prefers:

• auf der Nase

Both systems are normal in their own language.

Yes. German very often forms compound nouns by joining words together.

• Sonne = sun
• Brand = burn

Together:

• Sonnenbrand = sunburn

This is completely normal in German. English sometimes writes similar ideas as one word too, but German does it much more consistently.

Because all German nouns are capitalized.

So in this sentence:

• Schwester
• Sonnenbrand
• Nase

are all capitalized because they are nouns.

Adjectives and verbs are not capitalized here:

• meine
• hat
• leichten
• auf
• der

No. Here leicht means slight, mild, or not severe.

So:

• ein leichter Sonnenbrand = a slight/mild sunburn

This is a common use of leicht in German:

• leichte Erkältung = a mild cold
• leichte Schmerzen = slight pain

Yes, to some extent. German word order is flexible, but the finite verb in a normal statement usually stays in second position.

The neutral version is:

• Meine Schwester hat einen leichten Sonnenbrand auf der Nase.

You could also say:

• Auf der Nase hat meine Schwester einen leichten Sonnenbrand.

That sounds more like you are emphasizing where the sunburn is.

So the original sentence is the most straightforward, natural version for most situations.

Usually the main stress falls on the new or important information.

A natural neutral pattern would often stress:

• Sonnenbrand or
• Nase, depending on what is new in the conversation

For example:

• Meine Schwester hat einen leichten SONNENbrand auf der Nase.
• Meine Schwester hat einen leichten Sonnenbrand auf der NAse.

Also, in pronunciation:

• ei in meine sounds like English eye
• sch in Schwester sounds like sh
• Sonnenbrand is stressed on the first part: SON-nen-brand