Solar Activity
Light pollution from neighboring houses makes telescopic observing at night from my back yard nearly impossible. An additional obstacle has recently appeared. Milky white haze from western wildfire smoke blankets the sky. Each night I try using a telescope I'm reminded of why I decided to do solar observing during the day.
During morning daylight on September 10th haze and neighboring spotlights still(!) shining into my yard had no effect on the Sun! Conditions were excellent, with only a few small widely scattered clouds, a gentle puffing breeze, and temperatures ranging from 66 to 71 degrees. Three days earlier solar features were more impressive and well placed. By the time I could observe on the 10th, solar rotation had carried some sunspots around the western limb out of view. A large, complex sunspot group was still visible, however, along with other interesting features.
All sunspots were located in the western solar hemisphere as can be seen in the following 11-panel mosaic. (Click on images for larger views.)
The previous image shows no rim spicules or prominences because it was processed to show disk detail. The next image overexposes the disk but shows nice features on the rim.
All previous images were made by recording almost perfectly monochromatic red light with a wavelength of 656.28 nanometers. This particular red color is emitted by excited hydrogen atoms in the Sun's chromosphere. I tune the filter in my solar telescope to specifically transmit only this one wavelength. So the previous images show what hydrogen gas is doing in the layer of the Sun where the temperature and density have the right values to produce this particular excitation in hydrogen.
If I tune the filter so it transmits some other wavelength besides exactly 656.28 nanometers, the light my camera records will no longer come mostly from excited hydrogen. Instead, the camera will record red light capable of leaving the Sun from any thermally emitting solar material. In fact, the camera will record red light coming from the solar photosphere, the layer beneath the chromosphere. The photosphere emits a continuous spectrum of all colors which appears yellowish-white to our eyes. When the filter is tuned away from the 656.28 nanometer wavelength, the camera will record a red portion of this overall continuous solar spectrum.
The next image shows how the sunspots look when the filter is tuned away from 656.28 nanometers. Notice how many different umbras are visible, including several small ones in the lower active area. It's really a complicated arrangement of umbras! Notice also the mottled appearance of the solar disk not occupied by sunspots. This is caused by unresolved solar granules - columns of rising and falling gas in the photosphere. Unfortunately, some dark vertical stripes appear in the image which could not be removed because I failed to take a flat field for this image.
Although there were no impressive features in the Sun's eastern hemisphere, there was one interesting small prominence appearing in the last image below. Notice how this prominence is blending into a faint filament as the Sun rotates.
