The Dow Jones Industrial Average (DJINDICES:^DJI) is just one of several Dow Jones market trackers. The secular index will never invite any tickers from the railroading, airline, or electrical utilities industries -- because there are separate Dow indexes for these sectors.

If you want to track these industries, you'll have to look for the Dow Jones Transportation Average (DJINDICES:DJT) or Dow Jones Utility Average (DJINDICES:^DJU) instead. There's even a composite index that brings all 65 tickers together.

In the video below, Fool analyst Anders Bylund explains why you'll never see Duke Energy (NYSE:DUK) and its $48 billion market cap on the DJIA, nor the even larger Union Pacific (NYSE:UNP) railroad.

Fool contributor Anders Bylund and The Motley Fool have no position in any stocks mentioned. Try any of our Foolish newsletter services free for 30 daysWe Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.