About the Object

IC 4592, also known as the Blue Horsehead nebula, is a reflection nebula surrounding the star system Nu Scorpii and is also part of a much larger molecular cloud complex. The blue colors in the image are caused by Rayleigh scattering of starlight around some of the brighter stars in the image embedded in dust and gas. The red and orange sections of the image are predominantly dust clouds preferentially absorbing blue light while passing longer wavelengths. Dust particles in interstellar space are generally much smaller than those here on Earth's surface, typically ranging from 10nm to 0.1um in size making them more like particles of smoke than what we think of as dust. 

In addition to IC 4592, the largest, brightest reflection nebula in the image, you can also see IC 4601 on the upper right of the frame. The mechanism of scattering is the same, but with different stars scattering light off their surroundings. The bright blue star on the left edge of the image is Beta Scorpii, also known as Graffias which means "claws" in Arabic. The blue halo surrounding this star in the image is caused mostly by light scattered by the optics of the telescope itself. 

The Blue Horsehead is located at a distance of about 400 light years. This image captures a swath of sky approximately five degrees across, so the molecular cloud from which the Horsehead is formed is about 40 light years in size.