Η αναχώρηση για την Αθήνα είναι στις οκτώ και μισή.

Η is the feminine singular definite article, meaning the.

So:

• η αναχώρηση = the departure

The noun αναχώρηση is feminine, so it takes η in the nominative singular.

Αναχώρηση means departure.

It is a noun, not a verb. Greek often uses nouns in the same way English does in travel contexts:

• Η αναχώρηση = the departure
• Η άφιξη = the arrival

So this sentence is built around the noun departure, rather than saying something like it leaves.

Για usually means for or to, depending on context. Here it introduces the destination:

• για την Αθήνα = for Athens / to Athens

The noun after για goes in the accusative case. Since Αθήνα is feminine singular, the accusative article is την:

• nominative: η Αθήνα
• accusative: την Αθήνα

So:

• για την Αθήνα = for/to Athens

In Greek, place names and proper nouns often appear with the definite article much more often than in English.

So Greek commonly says:

• η Αθήνα = Athens
• στην Αθήνα = in Athens / to Athens
• για την Αθήνα = for/to Athens

English usually omits the with city names, but Greek often keeps the article.

Στις means at when talking about clock time.

It comes from:

• σε
  • τις → στις

Literally, it is a contraction of the preposition σε with the feminine plural article τις.

Greek uses στις with most hours:

• στις οκτώ = at eight
• στις δέκα = at ten

So:

• είναι στις οκτώ και μισή = it is at eight thirty

Because the word ώρα (hour) is understood in the background, and hours are treated grammatically as feminine.

That is why Greek says:

• στις πέντε
• στις οκτώ
• στις εννιά

A useful special case is:

• στη μία = at one o’clock

Here it is singular because one hour is singular.

Και μισή means and a half, so:

• οκτώ και μισή = eight and a half = eight thirty / half past eight

This is a very common way to tell time in Greek.

Examples:

• τρεις και μισή = 3:30
• έξι και μισή = 6:30

Because μισή is feminine, and it agrees with the implied word ώρα (hour), which is feminine.

Even though ώρα is not actually spoken here, it is understood:

• οκτώ και μισή (ώρα)

So Greek uses the feminine form:

• masculine: μισός
• feminine: μισή
• neuter: μισό

In time expressions like this, the feminine is the normal one.

Yes. The omitted word is ώρα (hour).

So the full idea is roughly:

• στις οκτώ και μισή ώρα

But Greek normally leaves ώρα out in this kind of expression. Native speakers simply say:

• στις οκτώ και μισή

Yes. In everyday Greek, you may also hear:

• στις οκτώμισι

This means the same thing as:

• στις οκτώ και μισή

Both are natural. The version in your sentence is very standard and clear.

Είναι means is.

The structure is:

• Η αναχώρηση ... είναι στις οκτώ και μισή.
• The departure ... is at eight thirty.

So the sentence links the subject η αναχώρηση with the time expression στις οκτώ και μισή.

Yes. Greek word order is more flexible than English word order.

The sentence as given is neutral and natural:

• Η αναχώρηση για την Αθήνα είναι στις οκτώ και μισή.

But you could also move parts around for emphasis, for example:

• Στις οκτώ και μισή είναι η αναχώρηση για την Αθήνα.

This would put more focus on the time. The original version is probably the best one for a learner to use first.

A rough pronunciation guide is:

• ee ana-HO-ri-see ya tin a-THEE-na EE-ne stis ok-TO ke mi-SEE

A few helpful notes:

• η / ι / υ / ει / οι are all pronounced like ee
• θ sounds like th in think
• χ in αναχώρηση is a throaty sound, not like English ch
• the written accents show which syllable is stressed:
  • αναχώρηση
  • Αθήνα
  • είναι
  • μισή

Yes, people would say it, especially in travel, transport, and announcement contexts.

It sounds perfectly natural for things like:

• train schedules
• airport announcements
• ferry information
• travel bookings

In casual speech, someone might also use a verb instead, such as φεύγει (leaves), but Η αναχώρηση... is very normal in timetables and formal information.