the Hubble Space Telescope began collecting data from the far reaches
of the universe more than ten years ago, the public has been treated
to striking images of stars forming, galaxies merging and other
cosmic phenomena. But Hubble itself does not produce the colors
in these amazing images. Astronomers add the jewel-toned hues, using
software such as Photoshop.
that the practice constitutes false advertising of the universe.
But the Hubble astronomers say that they are not drawing colors
on the celestial objects, but rather that they are drawing colors
out of the Hubble images.
In other words,
Hubble gathers data about the universe's features through layered
images in gray. Hubble astronomers make multiple long exposures
to draw out whatever color is present in the celestial object,
using filters to block all but certain wavelengths of light. The
filters, like those of television screens, are red, green and
blue, because they can produce all the colors of the rainbow.
Once the unwanted
light is filtered out, astronomers record the remaining light,
producing images with colors that are more intense -- or sometimes
less intense -- than the original tones, according to Zoltan Levay,
imaging resource lead at Space Telescope Science Institute, which
produces many of the Hubble images. Astronomers can also assign
colors based on the object's chemical composition or other physical
characteristics, he added, or if an image is taken outside the
visible light spectrum, the processors can choose colors arbitrarily.
In some instances,
a color is selected to better present the information, as was
the case with the Eagle Nebula, Levay explained in an interview
with the Online NewsHour. The towers of gases in the popular 1995
image were depicted in green -- even though the predominant gas,
hydrogen, fits into the red part of the spectrum -- in order to
separate it visually from sulfur, another element with a red wavelength.
are a concern to some. Kenneth Brecher, a professor of astronomy
at Boston University, said at a 2002 meeting of the American Astronomical
Society in Albuquerque, N.M., that while the Hubble astronomers
are not doing anything deceptive, the fact that the colors are
drawn out is not always communicated well in the media. The process
is also highly subjective, he said.
color of objects that astronomers release are not really representative
of a thing one might imagine exists, which is the objective color
of a star or a galaxy," Space.com quoted Brecher as saying.
"Color is a very, very subjective phenomenon. Color is in
the eye of the beholder."
people were to travel to some of the cosmic phenomena that Hubble
imaged, they would often find much fainter, mostly white objects.
That's why humans use telescopes, which are designed to capture
light and color in ways the human eye cannot, Levay said.
from Hubble are not meant to produce a literal interpretation,
but rather a picture that represents as much information as possible
-- such as temperature, velocity or an object's material composition,
he said. And, "sometimes it's just a matter of aesthetics,"
of Hubble images -- the oddly shaped stair-step effect -- comes
from the use of the Wide Field and Planetary Camera 2, or WFPC2.
WFPC2 is made up of four cameras, one of which magnifies the view
of the object. When the magnified view is reduced to match the
proportion of other three images, the shape of the entire picture
changes from a rectangle to a stair-step shape as seen in the
Eagle Nebula (left).
Other orbiting observatories provide images that are later colorized,
including the Chandra X-ray Observatory. And after the James Webb
telescope is launched, more information will be gathered from
even earlier reaches of the universe that astronomers will then
seek to explain in a way that can be visually understood.
By Larisa Epatko, Online NewsHour