Is Wall Street praying for a papal pop?

Wall Street's benchmark stock index has a habit of rising when the head of the Catholic Church comes to town to speak to the United Nations. But it might take a small miracle in the case of Pope Francis's U.N. visit on Friday, since the S&P 500 (spx) is down more than 2 percent for the week as of midday Thursday.

"I'm not sure it's his highest priority," Howard Silverblatt, senior index analyst at S&P Dow Jones Indices, said of Pope Francis, known for his message of helping the poor. Indeed, as Pope Francis famously asked in 2013: "How can it be that it is not a news item when an elderly homeless person dies of exposure, but it is news when the stock market loses two points?"

The U.S. stock market's benchmark index has switched back and forth between weekly gains and declines for the past 11 weeks, a pattern that has not occurred since the mid 1970s, calculates Silverblatt,

The pontiff's speech will mark the fifth by a pope to the international body, and in all four prior incidences the S&P 500 advanced that day, with a collective average of 0.8 percent, the veteran Wall Street observer said.

When Pope Benedict XVI addressed the U.N. on April 18, 2008, the S&P 500 closed the day up 1.8 percent. Pope John Paul II's first U.N. address came on a day that had the index up 0.9 percent, followed by an Oct. 5, 1995, U.N. speech that coincided with a 0.2 percent gain. And, Pope Paul VI's Oct. 4, 1965, address to the body coincided with a 0.2 percent advance by the S&P 500.

The pontiff heads to town with the odds stacked against the weekly advance required for the continuing alternating pattern. If his address can overcome a negative 2 percent handicap "between now and the end of tomorrow, I'll give due credit, although I'm not sure I'll convert," Silverblatt quipped.