Observamos una galaxia y una nebulosa.

Observamos is the first-person plural form of observar, so it means we observe or we are observing in many contexts.

However, this form can also mean we observed in the preterite. Spanish sometimes uses the same form for both the present and the simple past in the nosotros form, so the exact meaning depends on context.

Spanish often leaves out subject pronouns when they are not needed. The verb ending already tells you who the subject is.

• observamos = we observe / we observed

So Nosotros observamos una galaxia y una nebulosa is possible, but usually nosotros is omitted unless the speaker wants emphasis, contrast, or clarity.

Because the sentence is talking about two separate things:

• una galaxia = one galaxy
• una nebulosa = one nebula

Repeating the article makes that clear and sounds natural in Spanish. In English, we also usually repeat it: a galaxy and a nebula.

If you left out the second una, the sentence would sound less natural in a normal context.

Both nouns are grammatically feminine, which is why they use una rather than un.

• la galaxia
• la nebulosa

This is mostly a vocabulary fact you have to learn with each noun. In these two cases, the ending -a matches the common pattern for feminine nouns.

Normally, and is y in Spanish.

It changes to e only before words that begin with an i sound, such as:

• padre e hijo
• España e Italia

Here, the next word is una, which begins with a u sound, not an i sound, so y stays the same:

• una galaxia y una nebulosa

Yes. This sentence follows a very straightforward pattern:

• Observamos = verb
• una galaxia y una nebulosa = direct object

So it is basically:

• We observe a galaxy and a nebula

Spanish word order is often flexible, but this verb + object structure is very common and natural.

Yes. This is an important point.

For -ar verbs, the nosotros form in the present and the preterite can look exactly the same:

• observamos = we observe / we are observing
• observamos = we observed

Usually the surrounding context tells you which meaning is intended.

In standard Spain Spanish, galaxia is pronounced approximately ga-LAK-sya.

A rough guide:

• ga as in gala
• lax with a clear ks sound
• ia often sounds like ya together

So the ending is not usually pronounced like two fully separate syllables in slow English-style speech; it tends to flow as -sya.

In Spain Spanish, nebulosa is approximately neh-boo-LO-sa.

A few points:

• ne = like neh
• bu = boo
• stress is on lo
• s is a normal s sound

So: ne-bu-LO-sa.

Not in this exact sentence, because there is no letter z in galaxia, nebulosa, or observamos.

But if you are learning Spanish from Spain, it is useful to know that z and c before e/i are usually pronounced with a th sound, like in thin.

For example:

• cielo → begins with a th sound in most of Spain
• luz → ends with a th sound in most of Spain

That feature does not affect this sentence, but it is part of Spain Spanish pronunciation more generally.