In 1995 the Hubble science team released the image of the “Pillars of Creation.” This photograph fundamentally changed the way most of us think of astrophotography. Yes, the high resolution and image details were quite impressive, but it was the color palette that made this image unique. I have written individual columns about nebulae, astrophotography, astronomical filters, and a bit of spectroscopy, but these topics all come together to create these “assigned color” photographs.
The Pillars of Creation are part of the Eagle Nebula, which was discovered in the eighteenth century and is the 16th object on Charles Messier’s list of “fuzzy things that are not comets.” It was first photographed in the late nineteenth century and had been a regular late twentieth century target for astronomers using film cameras. While the first images were black and white, color film can produce some really nice images that would match (at least somewhat) what we might be able to see with our naked eyes if they were sensitive enough.
Because the Hubble telescope was primarily a science mission, there was great interest in studying the composition of the universe by looking at specific wavelengths of light. Each element has its own unique spectral signature, or fingerprint, so looking for a certain wavelength of light associated with a specific element will reveal the distribution of that element. For example, excited hydrogen atoms emit a prominent red line at 656 nanometers, and taking a photograph through a filter that passes 656 nanometer light will show the distribution of hydrogen atoms.
Narrowband filters are made by building up multiple layers of dielectric coatings on a glass surface. These coatings are the same as the anti-reflective coatings you can get on your eyeglasses, but by using specific thicknesses and layers, selected wavelengths of light can be allowed to pass through, while others are reflected.
Instead of simply looking at one element at a time, it is possible to associate an element to one of the red, green, or blue portions of a 3-color photograph. In what is now called the Hubble Palette, a line of sulfur was assigned to be red, a line of hydrogen was assigned to be green, and a line of oxygen was assigned to be blue.
Narrowband filters are now readily available, although they are not cheap. As the quality of digital cameras has improved over the last couple of decades, so has the quality of Earth-based narrowband images. It is easy to recognize narrow band images because of the vivid colors, instead of the overall magenta tones from hydrogen gas seen in “natural” light.
As the use of the Fort Lewis observatories continue expanding, I hope that more of these narrowband images will be produced locally.
Hubble image updates
Astronomy picture of the day
An Astronomer’s forecast for Durango
Old Fort Lewis Observatory
- Jupiter and Saturn are in an ideal place in the southern sky for binocular or telescope observations this month. For even small telescopes, both planets are great targets to look at. Jupiter was at opposition, its closest approach to Earth, on Nov. 3.
- Uranus is at opposition on the 13th. While it isn’t usually included as one of the “visible” planets, Uranus can be seen with the naked eye from a dark location. Right now it is between Jupiter and the Pleiades. Binoculars will make the task significantly easier, but don’t expect more than a blue-green dot, even with a large telescope.
- Venus is the bright morning star. You can see it during the daytime, as it is certainly bright enough. Its position relative to the sun won’t change during the day, so if you notice how far from the sun it is at dawn, it will remain that same distance away all day.
- The Leonids meteor shower peaks on the nights of the 17th and 18th. Caused by dust from the comet Temple-Tuttle, it is expected to be around 15 meteors per hour this year, or double what a night without a meteor shower is.
Charles Hakes teaches in the physics and engineering department at Fort Lewis College and is the director of the Fort Lewis Observatory.