Question 1: The death of Socrates is usually said to have happened in 399 BC, but I've sometimes seen a question mark after the date. Is there actually a possible uncertainty about the exact year? What sources is the date based on? Xenophon? Plato? What is the chain that connects this to the modern calendar?

Question 2: It sounds like his death happened early in the month of Skirophorion, so maybe June or July. Is this about as accurate as we can be, June/July? As far as I can tell, the [Attic calendar](http://en.wikipedia.org/wiki/Attic_calendar) had vaguely defined months, and there may be no way of matching a particular month in a particular year to the Gregorian calendar.

The clearest discussion I've found is in the Stanford Encyclopedia of Philosophy: 

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> In the month of Thargelion [May-June 399 Apology] a month or two after Meletus's initial summons, Socrates's trial occurred. On the day before, the Athenians had launched a ship to Delos, dedicated to Apollo and commemorating Theseus's legendary victory over the Minotaur (Phaedo 58a-b). [...] Although the duration of the annual voyage varied with conditions, Xenophon says it took thirty-one days in 399 (Memorabilia 4.8.2); if so, Socrates lived thirty days beyond his trial, into the month of Skirophorion.
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Would the ship have been launched on the 6th or 7th of Thargelion, which were the days of the Thargelia purification ritual?