In 1878, Sir Sanford Fleming proposed dividing the world into 24 time zones, each spaced 15 degrees of longitude apart. The contiguous United States was covered by four time zones. By 1895, most states had begun to institute the standard time zones of Eastern, Central, Mountain, and Pacific on their own. But it wasn’t until 1918 that Congress passed the Standard Time Act, establishing official time zones in the United States.