Hello, fellow stargazers.
In 1995, the Hubble science team released images of the Pillars of Creation. This photo fundamentally changed the way we think about astrophotography. Yes, the high resolution and image details were very impressive, but what made this image unique was the color palette. I’ve written separate columns on nebulae, astrophotography, astronomical filters, and a bit of spectroscopy, but all of these topics come together to create this “assigned color” photo.
The Pillars of Creation are part of the Eagle Nebula, discovered in the 18th century, and are the 16th object on Charles Messier’s list of “obscure things that are not comets.” The star was first photographed in the late 19th century, and was a regular target for astronomers using film cameras in the late 20th century. The first images were black and white, but color film, if sensitive enough, can produce very nice images that match (at least to some degree) what the naked eye sees.
Since the Hubble Telescope was primarily a scientific mission, there was great interest in studying the composition of the universe by observing specific wavelengths of light. Each element has its own spectral signature, or fingerprint, so looking for specific wavelengths of light associated with a particular element reveals the distribution of that element. For example, an excited hydrogen atom emits a noticeable red line at 656 nanometers, and if you take a photo through a filter that passes light at 656 nanometers, you can see the distribution of the hydrogen atoms.
Narrowband filters are made by building multiple layers of dielectric coatings on a glass surface. These coatings are similar to anti-reflective coatings on eyeglasses, but with specific thicknesses and layers, they allow selected wavelengths of light to pass through and reflect other wavelengths.
Instead of simply looking at one element at a time, you can associate elements with one of the red, green, or blue parts of a three-color photo. In what is now called the Hubble palette, the sulfur line was assigned red, the hydrogen line green, and the oxygen line blue.
Narrowband filters are not cheap today, but they are easily available. As the quality of digital cameras has improved over the past few decades, so has the quality of narrowband images of the Earth. Narrowband images are easy to recognize because of their vibrant colors, rather than the overall magenta color caused by hydrogen gas seen in “natural” light.
As use of the Fort Lewis Observatory continues to expand, we hope to see more of these narrowband images produced locally.
Hubble image update
Astronomical photo of the day
Astronomers’ forecasts for Durango
Old Fort Lewis Observatory
hakes_c@fortlewis.edu
this month
- This month, Jupiter and Saturn are in ideal positions for viewing with binoculars or telescopes in the southern sky. Both planets are great targets to observe, even with a small telescope. On November 3, Jupiter was at opposition and closest to Earth.
- On the 13th, Uranus will be at opposition. Although Uranus is not normally included as one of the “visible” planets, it can be seen with the naked eye, even from dark locations. It is currently located between Jupiter and the Pleiades star cluster. Binoculars make the job much easier, but don’t expect to see more than a blue-green dot, even with a large telescope.
- Venus is the bright morning star. It’s bright enough that you can see it even during the day. Its position relative to the sun does not change during the day, so if it notices its distance from the sun at dawn, it will remain at the same distance throughout the day.
- The Leonid meteor shower will reach its peak on the nights of the 17th and 18th. Dust from Comet Temple-Tuttle is expected to produce about 15 meteors per hour this year, twice as many as on a night without a meteor shower.
Charles Hakes teaches in the Department of Physics and Engineering at Fort Lewis College and is director of the Fort Lewis Observatory.
