Pendleton, OR
ASG Observatory
NGC2244
IC405, IC410, IC417, NGC1931
NGC 3372
NGC 1499
NGC7000
M45
Horsehead & Flame Nebula
Barnard 33
To me, the understanding of light is essential to understand astronomy and the viewing of distant objects. The path that light takes is extraordinary, and the process of how it works and reacts with eyes, cameras, earth, and objects is equally interesting.
The visible light spectrum is a small portion of the electromagnetic radiation range. There are many waves on this scale such as radio waves, microwaves, infrared, ultraviolet, x-rays, and gamma rays. While we only see in the spectrum on this large range, we can listen and observe on many levels.
Photo Credit: NASA
Within this range is the visible light we see in astronomy and telescopes either with our own eye (visual mode) or with narrow band imaging in particular ranges using filters. The violets get down close to ultraviolet and are not viewable with the human eye, while the red heads toward the infrared range of light.
| Human visible light spectrum | |
|---|---|
| Color Range | Light Wavelength (nanometers or NM) |
| Red | 625 – 740 |
| Orange | 590 – 625 |
| Yellow | 565 – 590 |
| Green | 520 – 565 |
| Cyan | 500 – 520 |
| Blue | 435 – 500 |
| Violet | 380 – 435 |
To make the understanding easier, most computer monitors, digital cameras, and printers will lean toward the RGB scale, which breaks these light paths into Red (r), Green (g), and Blue(b) to make up almost all visual displays we see in print and screen. Back to your kindergarten mixing of colors and you can create nearly any image using these 3 colors.
With regards to astronomy, your visual planet viewing through an eye piece will occur within the visible spectrum and you will see the range of colors. When you connect a DSLR or CMOS camera to your telescope, you will have those converted from analog signals to digital signals in RGB to create your imaging.
Hubble Space Telescope uses monochrome black and white images to represent each spectrum… as do many amateur astrophotographers. Put a filter in your scope to block out all light except a small narrow range 3nm-12nm wide and you are collecting very precise light spectrums in black and white monochrome. Why? because monochrome images are 4x more precise than color pixels. With monochrome images, you can capture a red layer, a green layer, and a blue layer and combined them digitally to create the same image at 4x the quality.
Another way to imagine this is that a pixel in black and white is either on/off, but an RGB pixel uses 4 (1Red, 2Green, 1Blue) to represent the color as it comes in. No wonder Hubble uses this process.
While a photon is technically a traveling electron, think of it as a time traveler, where physics breaks down. Light is a massless photon that has traveled millions of miles, only to come through our atmosphere and enter your telescope from a distant object. It’s a fascinating journey, traveling at around 186,282 miles per second….
As atoms are excited by energy, in our case a good example would be hydrogen as it’s so common in the universe, the hydrogen atom electrons bounce up to higher orbits and then back down… causing the release of photons. These photons of light and the wavelength they come to us as tell us all about how they originated and from what. Hydrogen Alpha or Hydrogen Beta give off different light wave lengths, and we can use filters to differentiate them. Oxygen and Sulfur are also popular wave lengths to filter and thus create the images we see today in most astronomy photos.
Photo Credit: ZWO
Hubble has made famous its color palette by matching Sulfur to the Red channel, Hydrogen to the Green channel, and Oxygen to the Blue channel in most images. Because these monochrome black and white images can be combined in anyway you visual like, renditions in this color palette show amazing detail and distinguishable features in various nebula and bodies in space.
Hydrogen Image with Stars Removed. This image uses a filter – Ha (Hydrogen Alpha) that is 7nm wide at the 656nm light spectrum scale.
Sulfur Image with Stars Removed. This image uses a filter – SII (Sulfur-II) that is 7nm wide at the 672nm light spectrum scale.
Oxygen Image with Stars Removed. This image uses a filter – OIII(Oxygen-III) that is 7nm wide at the 496nm light spectrum scale.
This is a fully combined image that takes the Hydrogen, Oxygen, and Sulfur images and combines into an RGB image and then processed in a photo editor to enhance the colors for visual pleasure. The key to a good image is the processing, while data is still there and retained, certain attributes are enhanced and brought out to bring the HST color palette image to life.
OK, I lied, this was still in monochrome, but this is what it would look like in the visual spectrum, taken using RGB filters which cover most of the visible spectrum… of course our eyes still can not soak up light enough to see this, we can get a good idea given longer exposures in this color palette.
From start to finish, the photons travel millions of miles to us and land in our digital cameras and DSLR’s and we convert that photon into a digital signal and then combine or process images to bring them to light. Our eyes are not able to see many of these heavenly bodies, but with technology in the recent years, we can easily do it from our homes and with incredible results.
If you are looking for more information on astronomy and astrophotography basics there are some great resources available online to check out.
Astrobackyard.com – Trevor Jones at Astrobackyard has done a great job over the years introducing hundreds if not thousands to astronomy and astrophotography with his good videos and tutorial content.
Telescopeguide.org – Good site with comprehensive guides. We really like this guide on remote telescopes and astrophotography.
photographingspace.com – Dylan O’Donnell has some great video tutorials as well and complements astrobackyard videos in many ways.