Это была большая удача.

Here это points to some situation, event, or fact already known from the context.

Depending on the context, English might translate it as this, that, or it. In sentences like this, Russian very often uses это to mean the thing we’re talking about.

So Это была большая удача is structurally something like That/It was great luck.

Good question. In this sentence, большая удача is in the nominative, and in this common pattern Russian often makes the past-tense form of быть agree with that noun phrase:

• Это был хороший день
• Это была ошибка
• Это было чудо

Since удача is feminine singular, you get была.

So:

• удача → feminine
• therefore была

It is nominative singular: удача.

It is not a direct object here. It is the noun that names what это was. In other words, it is the predicate noun.

That is why the basic form appears:

• удача = nominative singular

Because adjectives in Russian agree with the noun they describe in gender, number, and case.

Here the noun is:

• удача = feminine, singular, nominative

So the adjective must also be:

• большая = feminine, singular, nominative

Compare:

• большой шанс — masculine
• большая удача — feminine
• большое счастье — neuter
• большие проблемы — plural

Yes, it is completely natural.

Russian often uses большой / большая / большое in places where English prefers great, very good, or major. So большая удача is a normal way to say something like:

• great luck
• a stroke of luck
• a very lucky thing

So even though the literal words are close to big luck, the phrase itself is idiomatic and natural.

Yes, that is also possible.

But notice that if you say that version, two things change:

• было instead of была
• удачей instead of удача

So you get:

• Это была большая удача
• Это было большой удачей

Both are grammatical, but they are built a little differently.

A simple way to think about it:

• Это была большая удача = a straightforward identification
• Это было большой удачей = more of a characterization or evaluation

For a learner, Это была большая удача is an excellent neutral model to remember.

Yes, Russian word order is flexible, but the neutral, standard order here is:

• Это была большая удача.

Changing the order usually adds emphasis, contrast, or a more literary tone.

For example, a rearranged version may sound more marked or expressive, not like the basic default sentence. So unless you have a reason to stress a particular word, the original order is the best one to use.

Not in the past tense.

Russian normally omits the verb to be only in the present tense:

• Это большая удача. = This/That is great luck.

But in the past tense, you need the past form:

• Это была большая удача.

So:

• present: no есть
• past: была is required

Usually not in a neutral standalone sentence.

If you just say:

• Была большая удача

it usually sounds incomplete, like part of a larger sentence or something very context-dependent.

Это is what anchors the sentence and means this/that/it. It makes the statement complete.

Because Russian has no articles.

Russian nouns appear without words like a, an, and the. The listener understands the meaning from context.

So удача here can correspond to English expressions like:

• a stroke of luck
• great luck
• sometimes the luck in another context

English has to choose an article; Russian does not.

The main stresses are:

• Э́то была́ больша́я уда́ча.

A rough pronunciation guide:

• Э́то → EH-tə
• была́ → by-LA
• больша́я → bal-SHA-ya
• уда́ча → oo-DA-cha

A few useful notes:

• была́ is stressed on the last syllable
• уда́ча is stressed on да
• unstressed vowels in Russian are often reduced, so the spoken form is less exact than the spelling

They are close, but not always identical.

• удача often means luck, success, or a lucky break
• везение is more like luckiness or good luck as a circumstance

In this sentence, удача sounds very natural. It is a common and idiomatic choice for saying that something was a very lucky thing.