The origin of the holiday half day of trading on Wall Street

Some traders on Wall Street are among those trudging into to work today for the traditional half day of stock trading after Thanksgiving.

In the early 1930s, a financial crisis shut the stock market down for days, and the exchange didn’t tell investors when it would reopen.

Economic historian John Steele Gordon said a federal law passed several years later so that wouldn’t happen again.

“The stock exchange is forbidden to close more than three consecutive days," he said.

That's why markets are generally open on Friday holidays.