This light shows us layers up to 1700 km above the sun's visible surface and is especially important for imaging the lower chromosphere. The lower chromosphere is the coolest layer in the sun's atmosphere. The H alpha picture of the sun is very useful in predicting eruptions. The bright regions around sunspots, called plages, and brilliant solar flares are easily seen at this wavelength. Filaments, vivid string-like regions, and sunspots, large blotches on the solar surface, appear dark.
Filaments are common sources of eruptions.
Filaments on the solar limb appear bright against the blackness of space and are called prominences. Dark splotches on the sun are sunspots. They are almost always seen in pairs and in groups of pairs. Sunspots are dark because they are the coolest places on the sun. The number of sunspots on the sun at any given time varies in an ll-year cycle as does the number and severity of disturbances in space weather.