15 June - Saint Vitus; Ember Day

Weather: If Saint Vitus Day be rainy weather, it will rain for thirty days together.

EMBER DAY: The weather today foretells the weather of July.

Astronomy:  Total lunar eclipse (and one of the longest this century) tonight (see EarthSky for details).  Visible from Europe, Africa, Asia, Australia, New Zealand, and southern and eastern South America.
[For the rest of us, not this time]

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Today is the feast of Saints Vitus, Modestus, and Crescentia, martyrs (died c. 303). 

"In Basilicata, near the river Silaro, the birthday of the holy martyrs Vitus, Modestus, and Crescentia, who were brought thither from Sicily, in the reign of Diocletian, and after being plunged into a vessel of melted lead, after being exposed to the beasts, and on the pillory, from which torments they escaped uninjured through the power of God, they ended their religious combats."

According to his legend, St. Vitus (French "Guy"; Italian "Vito" and "Guido") was a youth of twelve who was converted to Christianity by his tutor, Modestus, and his nurse, Crescentia.  His father, taking exception to this, had all three scourged and thrown in prison by the local magistrate.  They escaped and fled to Rome, where they were denounced as Christians and suffered martyrdom under Diocletian.

He is one of the Fourteen Holy Helpers, a protector of domestic animals, and invoked against epilepsy and against over-sleeping.  He is the patron of dancers and entertainers in general.

He was also an exceptionally brave young man.  We don't think of 12-year-old children being steadfast in anything [except dislike of vegetables] - the first hint of punishment and most of them knuckle under.  Vitus was tortured repeatedly, and still would not apostatize.

Why he is pictured with a rooster, I don't know.  Neither did Naogeorgus in his description of Saint Vitus:

"The next is Vitus, sod in oil, before whose image fair,

Both men and women bringing hens for off'ring do repair:

The cause whereof I do not know, I think for some disease,

Which he is thought to drive away from such as him do please."

An old bit of Latin might allude to the sacrifice of chickens, possibly because their jerky movements while scratching or while fighting reminded the sufferers of their own torments:

Ne nimium saltet, saliens formidine gallum

Mactat mortifero salsa puella pede.

His name is given to Sydenham's Chorea (known for centuries as Saint Vitus' Dance), a malady which causes sufferers to jerk uncontrollably.  Why he is associated with it, or with dancers, is disputed [to me, there is a lot of chicken vs egg here - which came first?]  But here are a couple of reasons for it (and you can find a little more discussion at Catholic Culture).

In his legend, Vitus cured the child of the Emperor Diocletian from demonic possession (Diocletian showed his gratitude by throwing Vitus to the lions, among other things.)  As epilepsy and other spasm-inducing illnesses were thought to be caused by the Devil, sufferers prayed that Vitus would cure them, as well.

A belief grew up in Germany that anyone who danced before the statue of St. Vitus on his feast day would have good health for a year.  The manic dancing resembled the movements of chorea sufferers, ergo, association with same.

One story about him is that while he was in prison, his father looked through the keyhole and saw Vitus dancing with angels (or that angels danced for him).  This is why he is a patron of dancers.

So, did he become a patron of dancers because he was invoked by those who suffered from involuntary spasms?  Or did he become the saint of epileptics because their movements resembled those of the dancers already under his patronage?  Who knows.