June 30 has been proclaimed by the United Nations as International Asteroid Day because it is the anniversary of the day a large explosion occurred in the sky over the Podkamennaya Tunguska River in Siberia, Russia in 1908 which is considered to be the largest asteroid impact on Earth in recorded history.

It destroyed about 2,000 square kilometers (770 square miles) of the forest in the area, flattening about 80 million trees. The area is sparsely populated, and there were no official reports of human casualties.

What are Asteroids?

Asteroids are solid rocky leftovers from 4.6 billion years ago when our solar system was formed. They orbit around the Sun and if they are large enough they are occasionally called planetoids or minor planets. Asteroids are mainly composed of minerals and rocks, while comets are made of dust and ice. Meteorites can be dust particles or fragments from a comet or an asteroid.
https://asteroidday.org/updates/news-updates/asteroid-day-press-release-2020/

Asteroid day was founded by Dr. Brian May of the rock band Queen who is also an astrophysicist, Rusty Schweickart of Apollo 9 B612 President Danica Remy and Grig Richters the filmmaker to promote awareness the importance of asteroids in our solar system history, and the role they play in our solar system today

After the impact in Chelyabinsk Russia on 15th February 2013 it was thought that the public and governments needed to learn more about asteroids to support the resources necessary to find and deflect asteroids. In 2016, the United Nations declared Asteroid Day as an official day of education through the Luxembourg Space Agency, which leads the global research and resources. For once countries around the globe have put aside their differences and work together combining the technology and information gathered from their observatories and satellites to investigate these phenomena and devise ways of protecting us from any more close encounters.