https://www.cnet.com/news/longest-total-lunar-eclipse-of-the-century-to-turn-the-moon-red-this-month/

The century is relatively young yet, but the longest total lunar eclipse of the 21st centenary is set to go down on July 27. In fact, it's probably the longest such event between now and 2123, according to NASA's catalog of such things.

A total lunar eclipse occurs when the sun, earth and moon are in a line, casting the reddish-orange shadow of our planet onto the surface of the moon.  This is why a total lunar eclipse is often referred to as a "blood moon."