April 6 Solar Sunday

Observe The Sun Safely! Never look at the Sun without a proper filter!
Solar Programs are held 1st Sunday of every Month 2:00-4:00 PM at Houge Park weather permitting.
We had a nice relaxing day of observing the sun at Houge after a very successful Earth Day solar program. One killer flare extending about 200,000 miles (25 Earth diameters) from the solar disc and a sunspot count of 172 (NOAA) made the day. About 10 folks stopped by throughout the session and one member George (who Dave sent by) and I had a nice discussion on solar filters.
Standard Solar filters for refractors, SCT, Dobs, and Newtonians can be bought direct from manufacturers like Orion Telescopes, 1000 Oaks, and Baader Planetarium. The performance difference is small between these filters and there are advantages and disadvantages such as hard glass or film (which has the consistency of a plastic foil).
Cloudy Nights has some reviews on these various filters. If you have a refractor another option is a Herschel wedge. It is a right angle prism adapter that attaches to the back of your refractor. Note: A Herschel wedge is not to be used with other type telescopes. Both Lunt and Baader sell these special prism devices pictured below.
The Baader wedge (above right) has a diffuser screen on back that can help centering the sun in the eyepiece. However it is more expensive than the Lunt (left). A neutral density filter (sometimes called a moon filter) or green filter can be threaded onto the above systems or screwed on to your favorite eyepiece to help contrast. A green filter that does a better job of delivering contrast is the Narrowband Baader Continuum (below) that also attaches to back of an eyepiece or back of a threaded 2 inch to 1.25 inch adapter. It also must not be used alone but with proper solar filter. It is a true narrowband green filter featuring 10nm half-bandwidth (HBW) at the passband of 540nm while giving very good spectral transmission (See graph below). The 2-inch filter is shown below but it also comes as a 1.25. It can be used with standard solar filters that attach to front of scope or a Hershel wedge attached to the back of a refractor. It can make photosphere detail like faculae and solar granularity (solar granulation is most contrasty around 540nm) pop a bit more. I enjoy my 80mm refractor with a Hershel wedge and this continuum filter but like with all amateur astronomy – aperture rules. A 10 inch scope cracks common sunspots open along with intricate detail of penumbra webbing as well as showing faculae and solar granulation.
Narrowband Continuum Filter pictured above can help contrast. It must not be used alone but be used with a standard solar filter mounting over front aperture of scope or in conjunction with a Hershel Wedge attached to the back of a refractor.

Astronomical observer for 20 years and optical engineer. I design non-imaging prism and reflector optics for commercial, medical and high-end retail lighting.

Posted in Articles, Education & Reference Info, Solar

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