Update: May 9, 2007

MAKING PICTURES

By Pam Eastlick for THE DEEP on line

Welcome to The Deep science and technology column where we cover topics from the deep sea to deep space and beyond.

We’ve looked at the night sky since we lived in caves and for most of human history; it was pretty much a study in black and white.  Mars and some stars like Betelgeuse and Aldebaran are noticeably red and other stars are definitely blue but still, black and white pretty much described it.

Then, in 1610, Galileo looked at the sky for the first time with a telescope and discovered that not only was Mars red, Saturn was a deep golden yellow and Jupiter had colored stripes.  Perhaps the sky wasn’t just black and white after all.

As telescopes improved, astronomers began to find fuzzy things in the sky that definitely weren’t stars and weren’t planets and weren’t comets.  Since there were healthy prizes for finding new comets, it became worth your while if you were a serious astronomer to have a list of those fuzzy blobs and their locations so you didn’t report them as comets and embarrass yourself.

It took many years before telescopes improved to the point that we learned just what these fuzzy objects were.  Many of them were called ‘planetary nebula’ (nebula is the Latin word for ‘fuzzy object), because in the small telescopes of the day, they looked like stars with planets around them.

In the 1930’s, Edwin Hubble, the astronomer for whom the Hubble Space Telescope is named, discovered that many of these ‘fuzzy spots’ were, in fact, gigantic star cities; galaxies like our own Milky Way.  But others were not galaxies and the larger telescopes of the last century revealed many of them were an astounding rosy red.

Each element in the periodic table produces a characteristic color when it’s converted to a gas.  This is the basis of spectroscopy, the science that allows astronomers to determine the elements a star contains, just by looking at its light.

Most of the nebulae scattered around the sky were that amazing rosy red because that’s the color produced by ionized hydrogen.  Ninety percent of all atoms are hydrogen and rosy red is the favorite color of the universe.

Most early sky photos were black and white because early photographic films recorded only black and white.  These photographs can be things of beauty in their own right, but with the development of color films, sky images began to take on a completely new dimension.

But interestingly enough, modern space photography has gone right back to black and white.  Most big telescopes (including the Hubble Space Telescope) don’t use color film — in fact, they don't use film at all.  Their cameras record light from the universe with special electronic detectors called CCDs.  These detectors produce images of the cosmos not in color, but in shades of black and white.
Taking color pictures with CCDs is much more complex than taking color pictures with a traditional camera or even a digital camera.  Finished color images taken with CCDs are actually combinations of two or more black-and-white exposures with the color added during image processing.  Scientists often use color as a tool, sometimes to enhance an object's detail or to see processes that ordinarily can’t be seen by human eyes.

Energy from astronomical objects comes in a wide range of frequencies.  Humans see only the very narrow range of frequencies called visible light.  CCD-equipped telescopes can detect all the visible wavelengths of light plus others that are invisible to human eyes, like ultraviolet and infrared light.
Astronomical objects look much different when viewed in different light wavelengths.  CCD-equipped telescopes use special filters that allow only a certain range of light wavelengths through.  Once the unwanted light is filtered out, the remaining light is recorded.

Most CCD cameras have many filters that allow them to record images in a variety of wavelengths.  Since the cameras can detect light outside the visible light spectrum, the use of filters allows scientists to see "invisible" features of objects — those only visible in ultraviolet and infrared wavelengths.
Many full-color CCD images are combinations of three separate exposures — one each taken in red, green, and blue light.  When mixed together, these three colors of light can simulate almost any color of light that is visible to human eyes.  Televisions, computer monitors, and video cameras recreate colors in the same way.

Some space images have colors assigned to different elements, like hydrogen, oxygen and nitrogen, while others have colors assigned to different temperatures.  Some images approximate reality – their colors assigned to make an object appear as it would if you saw it through the window of a spaceship, while other images bear no relation to the object’s actual appearance.

Just remember that the next time you see an astounding space image that creating color images from the original black-and-white exposures is equal parts art and science. 

LOOKING AT A NEARBY GALAXY
Taking pictures of an object in many different wavelengths can tell you a great deal about the object.
	This is a picture of the galaxy Centaurus A taken in visible light.  If we were a little closer to this galaxy than 13 million light years, it would look like this in our sky.
Visible Light

This picture shows you how Centaurus A looks in ultraviolet.  It tells you that many of the stars of Centaurus A are like our own Sun and shine more brightly in visible light than in the hotter temperatures of ultraviolet.
	Ultraviolet

This picture taken by the Chandra space telescope shows how this massive galaxy would appear if you were Superman.  This is Centaurus A in X-rays.  And no, the newswebmaster didn’t change the orientation.  Astronomers study Centaurus A because it’s an active galaxy.  There’s something going on at its core that’s sending huge fountains of X-rays into space at right angles to the rest of the galaxy.

X-ray

And the galaxy isn’t just sending up fountains of X-rays.  This picture shows Centaurus in radio waves.  And what’s causing those huge fountains of radio and X-rays? Astronomers are still debating the issue, but most agree that Centaurus A harbors a monstrous black hole at its core.  And we would never have known it from looking at the galaxy in visible light.
	Radio Waves

Although Centaurus A isn’t visible in the sky just by looking up, you can find its location in the southern sky (if you live in the tropics.)  Just find Crux the Southern Cross close to the southeastern horizon just after dark one night this week.  Hold your arm out full length and use your clenched fist as a measuring device.  Your clenched fist covers about 10 degrees of sky.

Measure up two-fist widths from the bottom star of the Southern Cross and one fist-width to the left from that point.  That’s the location of Centaurus A in your personal sky.