2012 11 14 – White Light/H-alpha Comparison | PCW Memorial Observatory

2012 11 14 – White Light/H-alpha Comparison

In the wake of the beautiful solar eclipse photos and reports from the 13th, the Sun was putting on spectacular shows in both hydrogen alpha and white light along with several M-class flares and auroral activity for the Northerners. Living in Texas, I missed out on both the eclipse and the Northern Lights but the views from my backyard through my solar filters gave me an appreciative fix regardless.

The chromosphere of the Sun can be viewed in the hydrogen-alpha spectral line that is centered on 6562.8 Angstroms by using a very narrow bandwidth filter such as a hydrogen alpha filter set or a spectrohelioscope. The photosphere can be viewed with a white light filter that transmits the entire visible spectrum of light but at a level that is safe for us by blocking out 99.999% of all available light. Other methods for viewing the photosphere include projection viewing where you project the solar image on a wall or other backdrop instead of viewing the Sun directly through the eyepiece. What an observer can expect to see in a hydrogen alpha (Ha) filter is quite different than what is seen in white light (as you can see from the comparison sketches below). For a better understanding of the “layers” of the Sun, please see the link from AstronomyOnline.org. Another informative site for what you can expect to see in hydrogen alpha can be found on The Prairie Astronomy Club site and is an article written by David Knicely called “Observing the Sun in H-alpha.”

The first sketch below of the chromosphere was rendered at the eyepiece while using a dedicated hydrogen alpha telescope, an internally double-stacked Coronado Maxscope Ha 60mm that has a very narrow bandwidth of close to 0.45A. The amount of disk detail that can be seen with this telescope is very high and contrasty. In the sketch below, you can see several active regions across the disk with brightened plage, sunspots within the plage, filaments and prominences (which are filaments that reach over the limb). Visually, I could see a mottling appearance from the chromospheric network.

Hydrogen alpha sketch created with black Strathmore Artagain paper, white Conte’ crayon and pencil, white Prang pencil, black oil pencil, charcoal pencil.

The following sketch of the photosphere was created at the eyepiece using a glass white light filter in front of the objective lens of a refractor. Features rendered in this sketch are faculae to the 9 o’clock position of the disk, sunspots, and limb darkening. Visually, and as shown in this sketch, you can expect to see more detail within the sunspots while viewing in white light than you can in h-alpha. Note that most of the sunspots have both penumbrae and umbrae. When seeing conditions are above average, you may see granulation in white light.