The Sun
The Sun is the closest star to the Earth. It is the source energy for almost all life on Earth. It is a dynamic body, with ever-changing features across its surface. At least when it's not during times of Solar Minimum (the designation for the period during its 11-year cycle when few to no sunspots are visible). The Sun was emerging from an unusually long period of Solar Minimum in 2010, when I started imaging the sun using a Hydrogen-Alpha filter. The solar H-alpha filter passes exactly the same wavelength of light as the deep-sky H-alpha filters I use for my nighttime deep sky images. However, the solar filter is a very different filter from the nightsky H-alpha filter. While the nighttime H-alpha filter is a glass disk permeated with the necessary coatings and filter materials to filter out all but the light of ionized hydrogen from faint deep sky objects, the solar H-alpha filter is a double system consisting of a front energy-rejection filter placed in front of the telescope's optics plus a second, blocking filter at the eyepiece end. The Sun is a very intense light source; there is no way that a deep-sky H-alpha filter can be used to safely gaze at the Sun. In other words, DON'T LOOK at the SUN WITHOUT A FILTER properly tuned and certified as safe for solar gazing.
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