The term “atmosphere” refers to the gaseous sphere around a solid celestial object, usually a planet. For example, Earth’s atmosphere is layers of such gases as oxygen, nitrogen, etc. The sun’s “atmosphere” consists of extremely hot radiations of the sun’s energy output. Since the sun is made of hydrogen being converted into helium, the “atmosphere” of the sun is composed of cooling atoms of helium; the sun’s surface is not hot enough to convert hydrogen to helium.
The Sun's atmosphere does exists and it is separated in three parts. The only part that can be seen is called photosphere and it represents the lowest layer of sun's atmosphere. The photosphere has several characteristics that can be examined with a telescope, such that: granules, dark sunspots and faculae. The temperature of photosphere varies between 4000 and 6000 Kelvin degrees.
Chromosphere is the layer located above Photosphere and it's temperature reaches about 10000 Kelvin degrees. At these temperatures, H-alpha emission occurs, which is the light emitted by hydrogen.
The outer layer of Sun's atmosphere is called Corona and it could become visible only during total eclipses of the Sun. The Corona's features are changing from one eclipse to other. and it's dynamic can be examined with satellites.
The sun is made up of four parts: the corona, the upper chromoshpere, the lower chromosphere, and the photosphere.
The Corona is the outer most layer of gas surrounding the sun. It is only visible to the naked eye during a solar eclipse.
The Chromosphere will appear as a red-ish haze during a solar eclipse.
The photoshpere is the deepest portion of the sun and is the part that gives off visible light.
The sun's atmosphere is extremely hot and its 'atmosphere' or corona, is mainly composed of Hydrogen and some Helium. The sun is able to produce Helium at its core and compresses Hydrogen under great heat and pressure until the nucleus of the atom combine to make Helium and this fuels the sun.