Natural colored whitelight image from the ground-based Blackbird Observatory.
Copyright © 2009 R. Jay GaBany

M-94 (NGC 4736) in Canes Venatici

Multi-spectral comparison imagery

Electromagnetic radiation is the primary method for transferring energy throughout the Universe. It's composed of particles, called photons, arranged in waves moving outward like ripples in a pond, traveling at a constant speed in all directions from its source. The distance between the crest of each wave can be less than a billionth of a centimeter (gamma rays) to more than a thousand kilometers in length (radio waves). Our eyes are sensitive to only a small portion of all possible wavelengths- those that our Sun releases in greatest quantity. We call this White Light. But, white light is nothing of the kind; it is a mixture of all visible wavelengths, each of which produces a different color when isolated. The shorter wavelengths yield violet and blue, the longer ones create orange and red. On either side of these familiar rainbow colors extend the other forms of radiation our eyes cannot perceive: gamma, X-rays and ultraviolet rays have wavelengths that are too short while infrared and radio waves are too long.

The space between the stars is not empty- it's filled with very thin amounts of molecular gas and dust. But, even a few molecules of this material per cubic centimeter can create a dense, opaque cloud when viewed from a distance of a hundred or more light years. These clouds can absorb the white light released by stars that lie further beyond making it difficult or impossible for us to see them visually. But, ultraviolet and infrared radiation is not so easily blocked thus allowing astronomers to pierce otherwise obscuring haze with images taken through filters that only pass these wavelengths.

This investigation of M94 was conducted by observing the galaxy in several wavelengths. White light images typically display this star system as an active central region surrounded by an amorphous circular band classically described as a closed stellar ring. Modern astronomical CCD cameras possess an incredible tonal range- far more than photographs produced with film emulsions. If great care is exercised, it's possible to preserve and enhance small contrast variances that are often overlooked to create a white light image that offers a tantalizing glimpse of orderly patterns within the surrounding ring. This investigation confirmed extensive structuring first detected in white light when M94 was viewed through infrared and ultraviolet wavelengths that penetrated the ring's fog of dusky material to reveal stars, star forming regions and extensive spiral arms for the first time.

Multi-spectrum viewer
Mouse over a thumbnail to view M94 in a specified wavelength.

Typical white light

Long exposure white light


Infrared 24 microns

Infrared: 8 microns

Infrared: 3.6 microns

Infrared composite

Click here to compare with a super-stretched version of the luminance data!

Click here for an animation showing how M94's spiral arms evolved from the surrounding ring.

Click here to see the original image!

Compare the confirmation image produced with data from the Spitzer Space Telescope by mousing over the above image.

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White light image:
January 30- February 5, 2006
RCOS 20- inch, SBIG STL-11000
550 minutes Luminance, 90 minutes Red, 54 minutes Green and 108 minutes Blue (All 1X1)