Vemos la Vía Láctea a simple vista.

In Spanish, subject pronouns are often omitted because the verb ending already tells you who the subject is.

• vemos = we see
• The -emos ending shows it is nosotros

So Vemos la Vía Láctea a simple vista is completely natural.
You could say Nosotros vemos..., but that usually adds emphasis or contrast, such as We see it, but others do not.

Vemos comes from the verb ver, meaning to see.

It is:

• 1st person plural
• present indicative

So:

• yo veo = I see
• tú ves = you see
• él/ella ve = he/she sees
• nosotros vemos = we see
• vosotros veis = you all see
• ellos ven = they see

The present tense is used here for a general fact: something that is generally true.

So Vemos la Vía Láctea a simple vista means something like:

• We can see the Milky Way with the naked eye
• The Milky Way is visible to us without instruments

Spanish often uses the simple present for general truths, just like English does in sentences such as Water boils at 100°C.

Because Vía Láctea is treated as a noun phrase, and in Spanish it normally takes the definite article:

• la Vía Láctea = the Milky Way

This is very common in Spanish with names of geographical or astronomical things. English often drops the article in some names, but Spanish may keep it.

Also, vía is a feminine noun, so the article is la.

They are capitalized because Vía Láctea is a proper name: the name of our galaxy.

So it works like other named entities:

• la Tierra
• el Sol
• la Luna
• la Vía Láctea

Whether words like sol, tierra, and luna are capitalized can depend on context, but Vía Láctea as the name of the galaxy is normally capitalized.

They have written accents because Spanish spelling rules require them.

• vía has stress on the first syllable: VÍ-a
• láctea has stress on the first syllable: LÁC-te-a

The accents show the correct stress and, in the case of vía, help mark that the vowels are pronounced in separate syllables rather than as a diphthong.

A simple vista is a set expression meaning with the naked eye or without optical aid.

So the sentence means that we can see the Milky Way:

• without a telescope
• without binoculars
• just by looking normally

It is an idiomatic phrase, so it is best learned as a whole chunk.

Because a simple vista is a fixed idiomatic expression in Spanish.

You should learn it as one phrase:

• a simple vista = with the naked eye / at first sight / visibly, depending on context

It does not normally take an article here, so a la simple vista would not be standard in this meaning.

Yes, absolutely.

• Vemos la Vía Láctea a simple vista = a general statement, more direct
• Podemos ver la Vía Láctea a simple vista = emphasizes ability/possibility, similar to We can see the Milky Way with the naked eye

Both are natural.
The version with podemos sounds a bit more explicit about the idea of being able to.

Because ver means to see, while mirar means to look at.

• ver = perceive with your eyes
• mirar = direct your gaze toward something

Here the idea is that the Milky Way is visible, so ver is the right verb.

Compare:

• Vemos la Vía Láctea = We see the Milky Way
• Miramos la Vía Láctea = We look at the Milky Way

The second one focuses more on the action of looking.

In standard Peninsular Spanish, a good approximation is:

• Vía: BEE-ah
• Láctea: roughly LAK-teh-ah

A few useful pronunciation notes:

• v and b sound very similar in Spanish
• í shows the stress in Vía
• á shows the stress in Láctea
• The c in Láctea comes before t, so it sounds like a normal k sound

A rough full pronunciation would be:

BEH-mos la BEE-ah LAK-teh-ah a SEEM-pleh BEES-tah

In much of Spain, v in vista is still pronounced like the Spanish b sound, not like English v.

The given order is the most neutral and natural:

• Vemos la Vía Láctea a simple vista

But Spanish word order is somewhat flexible. For example:

• La Vía Láctea la vemos a simple vista — adds emphasis to la Vía Láctea
• A simple vista vemos la Vía Láctea — emphasizes the manner, though this is less neutral

So yes, the order can change, but the original sentence is the plain, standard version.

It is general Spanish and would be understood everywhere.

Nothing in the sentence is uniquely Spanish from Spain, except that a learner focusing on Spain should note the usual Peninsular pronunciation. Grammatically and lexically, the sentence is standard across the Spanish-speaking world.

Yes. Besides with the naked eye, it can sometimes mean at first sight or visibly/apparently, depending on context.

For example:

• A simple vista, todo parece normal = At first sight, everything seems normal

But in Vemos la Vía Láctea a simple vista, the meaning is clearly with the naked eye.