1. In 1820, Maine became the 23rd state to join the United States. Prior to this, Maine had been part of the Commonwealth of Massachusetts. May 4 of that year marked the official admission of Maine as a state in its own right.

2. On May 4, 1852, construction began on the Portland Observatory - a landmark tower in Portland, Maine that was used to spot incoming ships and signal their arrival to merchants in the city. The observatory still stands today and is open for visitors to climb and enjoy panoramic views of the city and Casco Bay.

3. In 1927 on May 4, the first female governor of Maine, Margaret Chase Smith, was elected to the State Legislature. She went on to serve as a U.S. Senator, and her career was marked by both her pioneering accomplishments as a woman in politics and her independent-minded approach to governance.

4. May 4, 1970, was the date of the Kent State shootings, a seminal moment in the Vietnam War era where National Guardsmen opened fire on student protesters at Kent State University in Ohio, killing four students and injuring nine others. Although this event did not occur in Maine, it had a profound impact on the era and became emblematic of the unrest and sense of social upheaval that defined the time.

5. In 2010 on May 4, the Deepwater Horizon oil rig in the Gulf of Mexico exploded, leading to one of the worst environmental disasters in U.S. history. Though the rig and the spill were not located in Maine, the event had widespread reverberations for the region, particularly in terms of its impact on fishing and conservation efforts along the Atlantic coast.