The solar corona has a temperature of more than a million kelvins; the photosphere has a temperature of only about 6000 K. Why isn’t the corona significantly brighter than the photosphere?

Answer & explanation:

Despite the huge difference in temperature between the solar corona and the photosphere, in addition to the fact that the solar corona is the largest and outermost layer of the solar atmosphere (about 13 million kilometers), the photosphere becomes a visible surface region due to to the gases present in it, causing the body to stop being transparent, becoming opaque to light.

However, it is still possible to observe the solar corona in total eclipses, where the opacity to light extends across the sun, facilitating the visibility of the corona and other layers.

the reaction mixture contains some ammonia, plus a lot of unreacted nitrogen and hydrogen. the mixture is cooled and compressed, causing the ammonia gas to condense into a liquid. the liquefied ammonia is separated and removed. the unreacted nitrogen and hydrogen are then recycled back into the reactor .