Though much more can be said regarding our universe, galaxy, and solar system, not much more is necessary for acquiring correct physical sense of factors affecting our weather. Regardless of which way Earth acquired its atmosphere, our sun provides nearly all energy for maintaining its present state. Though probing the solar interior is very difficult, knowledge of physics and chemistry acquired here on Earth allows development of many plausible theories. Before these are discussed though, electromagnetic radiation should be explained. Characteristics of electromagnetic waves include frequency and wavelength. Because their propagation occurs with light speed, these are related, as expressions show. You can see that because wave speed is constant, large frequency (number of wave crests passing a point during a specific time period - i.e., how frequently) corresponds with small wavelength, and vice-versa. Waves of all possible characteristics comprise the electromagnetic spectrum, which varies between those with very large frequency (also very large energy) such as gamma rays, and those of very small frequency (very small energy) such as radio waves. The most relevant portion of the spectrum for us is visible light, which we see as colors between violet (large frequency) and red (small frequency). Thus, light from the sun is electromagnetic waves of this form.
Studying colors of light from our sun during 1802, Wollaston (a physicist) discovered that it does not form a continuous spectrum, but includes dark lines. Separating colors of sunlight using a prism during 1814, Johann von Fraunhofer rediscovered the lines, which he labeled with letters of the alphabet. With further study, Fraunhofer found 574 of such lines. Thus, the name Fraunhofer Lines is used for these. During 1859, Kirchoff and Bunsen discovered that although a hot solid object emits a continuous light spectrum, hot gases emit light of specific frequencies, corresponding with the spectral lines. Considering this, a connection was made among lines in the sunlight spectrum those emitted from heated gases, especially for Na (Sodium), which causes very pronounced sunlight spectral lines at .5890 µm & .5896 µm. The idea that dark spectral lines were the cause of a cancellation among light emerging from the hot sun (solar electromagnetic spectrum) and cooler gases of elements above the solar 'surface' was conceived. Further experimentation revealed that position of each element's spectral lines is unique, similarly as a person's fingerprint is considered so. Thus, a method for identifying elements in the sun (spectroscopy) was discovered, which led to great possibilities regarding solar theories.
Spectroscopy revealed that our sun consists mainly of H (Hydrogen) and He (Helium). During these original experiments, the .5876 µm spectral line for Helium matched no known element - it was then an element only known on the sun. Only later was it found on Earth. Thus, Helium is so named because of the Greek word Helios, meaning sun. Many strong spectral lines were found for H, which were labeled using Greek letters, i.e., H-alpha, H-beta, H-gamma..., for decreasing wavelengths. During 1885 Balmer discovered a mathematical relationship (using the good ol' trial & error method) among wavelengths for the H series lines. This became known as the Balmer series, and the limit as N approaches infinity the Balmer limit (.3646 µm). Hydrogen, with atomic number 1, is the simplest of all atoms; containing 1 proton and 1 electron. During 1913, a relation was found among energy of an electron orbiting the 'Bohr H atom' and H series spectral line frequency. Energy was imagined as being quantized - occurring with discrete amounts. Thus, an electron change from a higher to lower energy state causes emission of a photon. Similarly, absorption of a photon causes an electron change from lower to higher energy state. You may notice that N = 3 is the lowest possible value (called N = 1 in the energy diagram shown), called ground state, with wavelength .6563 µm; and N = infinity is the Balmer limit - highest energy state. The energy diagram for a H atoms is quite simple - ones for other elements are much more complicated (and cannot always be graphically represented well).
Continuing the story of solar composition, H and He abundance means that the most logical
cause of energy production in the solar interior is thermonuclear H to He fusion reactions
in the solar core. The molecular mass of H is 1.008, and that of He is 4.003. Thus, when 4 H
atoms fuse as 1 He atom, 4.032 mass units of H become 4.003 mass units of He + energy.
This is related with the E = m c2 often cited as 'Einstein's equation'. The extra
.029 mass units of each reaction is transformed as energy, causing the enormous heat amounts
our sun emits. This process is not so simple as described. It requires several intermediate
processes, which require an average of about 14 billion years!, a product of which are
positrons and neutrinos (which travel from the sun and generally thru your body, earth, and most
everything else). Such fusion reactions require a temperature of at least 10000000 °K, and the
solar core's temperature is typically estimated as 15000000 °K. The the distance from the core
at which temperature is not hot enough for initiating fusion, a radiation zone exists, and above
that, a convection zone, where the sun becomes cooler. Some people believe that convection also
occurs in the radiation zone. At the top of the convection zone is the photosphere - the solar
'surface'. This is the portion of the sun which we see, which has temperature of about 5800 °K.
The solar surface rotates, left to right as we face it, with period of about 25 days at its
equator increasing to 37 days at its poles. An interesting thing to notice is that almost all
rotation and orbiting is counterclockwise (as viewed from top or with our North Pole on top) -
cyclones, Earth's rotation, Earth's orbit, Sun's rotation, and I think even rotation of stars in
our Galaxy.
Text is copyright of Joseph Bartlo, though may be used with proper crediting.