Astrophoto: Stellar Nursery NGC 7129 by Bob Allevo

Prior to 1957, virtually all photographs of the sky were produced as monochrome, black and white images. In that year, Ansco, once the world’s largest supplier of professional films, papers, and photo chemicals, introduced Super Anscochrome and over the next twenty-four months, full color images of the heavens were being released by the larger observatories. Over the years technology has improved and the colors captured in astronomical imagery have become more vivid and meaningful. For example, the hues seen in the accompanying picture represent not only this scene’s true-to-nature pallet, but it also reveals what you are looking at, too.

Amateur astrophotographers began to experiment with color pictures shortly after the professionals, but it wasn’t until the early sixties that their full color images began to grace the covers of leading astronomy periodicals. The riot of hues presented in these early color photographs was unexpected and caused some to suspect they were artificial. Those concerns were put to rest, however, as the number of pictures from independent sources presenting the same set of hues for identical space places increased from a trickle to a flood.

99% of the material in the Universe is hydrogen and helium. Some of that is locked up in stars but the vast portion floats in the spaces between them. Because the distances between stellar bodies is huge, the density of this material is exceedingly thin but some of it is shepherded by gravity and exploding stars into enormous clouds that span light-years and eventually spawn new stars under the right conditions.

The remaining percentage of material in space is comprised of cosmic dust. This dust is exceptionally small- much smaller that our Earth-bound namesake that is typically fine bits of fabric, dirt, or dead skin cells. These tiny, irregularly shaped particles range from less than 1/100th of a micron to 10 microns in size, with each micron representing one millionth of a meter. For comparison, a particle of smoke is about 1/10th of a micron large. They are comprised of carbon compounds and additional materials that include silicon, oxygen, nitrogen, nickel and, most likely, other heavy elements. Because of its carbon content, this cosmic fluff has been compared to diamond dust- it stretches the imagination, but the universe is, in fact, filled with this stuff!

Cosmic dust originates from red giant stars and supernovae, although there are other sources. It’s created when material from the core of a dying star is expelled into surrounding space as grains of heavy elements that forms into a cloud of debris. Over time, these particles drift from the scene of their creation, mix with the hydrogen and helium suspended throughout space, are incorporated into the vast clouds that later incubate new stars and coalesce to form the planets which circle them. These seemingly insignificant free floating grains are responsible for much of the world we see around us. They are also responsible for the inhabitants of our planet (you and me), too!

Interstellar dust has several optical properties that are also of interest when it comes to viewing a deep space picture like the one featured with this article. For example, the striking blue color is produced by copious amounts of dust that is reflecting the light of the bright, young stars it still surrounds. The young stars are only about a million years old- babies from an astronomical perspective! They have blown a large, oddly shaped bubble in all that remains of the original collapsed gas and dust cloud that created them. This scene is about 3,000 light years from Earth toward the northern constellation of Cepheus.

Interestingly, the blue tinted dust seen in this picture was produced in the same manner that makes our skies on Earth the same color! For example, when the rainbow of colors that makes up the light spectrum are mixed together, as in Sun or star light, they seem almost white. When light from the sun strikes the earth’s atmosphere, some of it is reflected back to space but some of it bounces around before a glancing eyeball detects it. This bouncing is called scattering and its ability to color our sky and explain the blue color of dust in a distant nebula was first recognized by John William Strutt, 3rd Baron Rayleigh, a British physicist who discovered the element argon and the phenomenon known as Raleigh scattering back in the late 19th century.

Light is made up of weightless particles, called photons, that are arranged into waves. The distance between the tops of the wave crests for each color is different with blue light having a shorter wavelength than red. When light strikes an object that is larger than its wavelength, the color is reflected. The molecules of oxygen and nitrogen in our atmosphere are larger than a wavelength of blue light but smaller than a wavelength of red. Therefore, the gas in our atmosphere reflects blue light while the other colors in sunlight, including red, simply passes through. A similar situation creates the blue hues in this article’s featured picture. Instead of atmospheric gasses, however, the blue scattering comes from tiny particles of interstellar dust.

This beautiful picture was taken by Bob Allevo from his private backyard observatory in East Hartford, Connecticut on August 18, 2006. It was produced with a 12 inch Ritchey-Chretien telescope and a 3.5 Mega-pixel astronomical camera. It required almost six hours of cumulative exposure.

Do you have photos you’d like to share? Post them to the Universe Today astrophotography forum or email them, and we might feature one in Universe Today.

Written by R. Jay GaBany