Wavelength-Dependent Solar Limb Darkening with Smartphones, Solar Projection, and SalsaJ

Solar limb darkening is a prominent feature seen in white images of the Sun: the brightness of the solar disk is greatest at the solar center and decreases radially outward towards the limb. White light images can be used to examine and even model limb darkening; however, the limb-darkening effect is, in fact, wavelength dependent. Limb darkening is more pronounced at the blue end of the spectrum and less at the red end. We discuss a relatively simple method to examine the wavelength-dependent nature of limb darkening using solar projection, smartphone imaging, and SalsaJ software.