M42
Possibly discovered 1610 by Nicholas-Claude Fabri de Peiresc.
Independently found by Johann Baptist Cysatus in 1611.
Trapezium cluster found as multiple star by Galileo Galilei in 1617.
The Orion Nebula M42 is the brightest diffuse nebula in the sky, and one of the brightest deepsky objects at all. Shining with the brightness of a star of 4th magnitude, it visible to the naked eye under moderately good conditions, and rewarding in telescopes of every size, from the smallest glasses to the greatest Earth-bound observatories as well as outer-space observatories like the Hubble Space Telescope. It is also a big object in the sky, extending to over 1 degree in diameter, thus covering more than four times the area of the Full Moon.