1. On April 22, 1970, the first Earth Day was celebrated nationwide, including in the District of Columbia. The event brought attention to environmental issues and led to the creation of the Environmental Protection Agency later that year.

2. In 1864, President Abraham Lincoln signed a bill granting the District of Columbia limited home rule, giving residents the ability to elect local officials and manage some aspects of their own affairs.

3. On April 22, 1874, the first annual Arbor Day was celebrated in the District of Columbia, encouraging citizens to plant trees in their communities.

4. In 1969, the National Air and Space Museum was established in the District of Columbia, featuring exhibits and collections focused on the history of flight and space exploration.

5. On April 22, 1837, Georgetown University in the District of Columbia established the country's first school of dentistry, paving the way for advancements in oral healthcare education and research.