Spectroscopy: how to define it? This is a question you maybe could ask. Well, the answer will be the following.
It is a branch of physics that studies the electromagnetic radiation spectra emitted or absorbed by the matter. The spectroscopic analysis opens the possibility to discover the chemical composition and the physical state of the body emitting the same radiation. Newton was the first to deal with this subject. He understood that the light of the sun can be divided into different colors by using a prism. He found as well that a wave with a shorter wavelength (higher frequency) has a greater refraction angle.
Kirchoff proved experimentally that the spectra of solid bodies, liquid bodies or gaseous ones which present high pressure and white-hot coloration state are continuous. That means that colors appear one after the other without interruption. In addition, gases at low pressure, when incandescent, emit a number of bright rows over black setting (emission spectrum).
Kirchoff examined later another situation. He considered the dark rows produced by a gas which is between a continuous spectrum and the observer. He found that they occupy the same position of the bright rows made by the same gas when led to incandescence (absorption spectrum). When considering the emission spectrum, the observed characteristics are dependent on the source. On the other hand, in the absorption situation, spectra are linked to the gas which is set between the source and the observer.
Sun and stars are studied according to their absorption spectra. From the continuous spectrum, scientists derive the temperature of the celestial body. In addition, from the absorption spectrum, they understand the nature of gases constituting their atmosphere.
A demonstration of the emission sodium D lines using a wick with salt water in a flame.
Wikipedia states: “The emission spectrum can be used to determine the composition of a material since it is different for each element of the periodic table. One example is astronomical spectroscopy: identifying the composition of stars by analyzing the received light. The emission spectrum characteristics of some elements are plainly visible to the naked eye when these elements are heated. For example, when the platinum wire is dipped into a strontium nitrate solution and then inserted into a flame, the strontium atoms emit a red color. Similarly, when copper is inserted into a flame, the flame becomes green. These definite characteristics allow elements to be identified by their atomic emission spectrum. Not all emitted lights are perceptible to the naked eye, as the spectrum also includes ultraviolet rays and infrared lighting. An emission is formed when an excited gas is viewed directly through a spectroscope”.
Emission spectrum of hydrogen
“The above picture shows the visible light emission spectrum for hydrogen. If only a single atom of hydrogen were present, then only a single wavelength would be observed at a given instant. Several of the possible emissions are observed because the sample contains many hydrogen atoms that are in different initial energy states and reach different final energy states. These different combinations lead to simultaneous emissions at different wavelengths”. Wikipedia
A continuous spectrum is that emitted by a radiator of a black body. This is a theoretical concept used in physics to define an object that absorbs all the light hitting it. It could be as well a white-hot piece of steel or the core of a star. It is called blackbody because it doesn’t reflect the light since it absorbs all the energy. The radiation emitted is said black body radiation and the density of energy emitted is said blackbody spectrum.
The blackbody spectrum is represented as a curve with a characteristic bell shape. This is a representation dependent only on the temperature. It is not on the material of the body. Generally, stars have a row absorption spectrum and, in some cases, an emission spectrum. Science says that black rows over the continuous spectrum are due to the presence of a colder atmosphere that absorbs in a selective way the continuous emitted by the star.
Considering the black body diagram, physics are able to determine that the sun has a surface temperature of 5700K. From the absorption diagram, they can understand the composition of the elements inside the atmosphere of the sun.
Now, the basic question is the following: can spectroscopy reveal the temperature of the stars? Traditionally science has been assuming that stars are like the sun, just because they consider the sun as a star. As all my readers already know, since many years, and from the beginning, I have been pondering the geometry of the Earth. For this very reason I can say that, for sure, stars are very different from the sun. Notwithstanding, academics postulate that stars are suns, that they are incandescent bodies and that their colors reveal their temperatures, according to the black body diagram. For each color, they link the proper temperature. But, Is it really like this? And what about, if stars would be cold and not white-hot? Would it be really possible to get an emission or absorption spectrum anyway? All bodies that are over the absolute zero emit some radiation.
When you examine a cold body, a white one, for instance, you could say that it has a very low curve on the black body diagram. It will be represented by a peak that is not in the visible range. This is the reason why a cold body has to get illuminated to be seen: it emits with lower frequency. So, when a body emits in the visible field, has it to be actually hot?
Think, for instance, of LED diodes light: they emit light radiation but are not incandescent. LEDs are made by semiconductors in which electrons pass from an excited orbit to a more stable one, thus emitting energy. This energy sets into motion a number of etherons and a light wave starts oscillating. LEDs light thus is not generated by a Joule effect and it doesn’t become incandescent.
How can we insert the light emitted by a LED in the black body diagram? It is cold light, so it is not dependent on temperature. Anyway, a continuous spectrum is emitted which is not related to the black body diagram. Below you can behold a spectrum of a light emitting diode.
Inside my blog, I have many times discussed both chemiluminescence as well as bioluminescence. Chemiluminescence occurs when one of the products of a chemical reaction is set into an excited state. When a similar chemical reaction occurs inside a living body, you call it bioluminescence. These reactions occur exothermically. They catalyze through an enzyme, the luciferase, that diminishes the necessary energy and consequently the final temperature.
The emitted light has a continuous spectrum with frequencies that are high enough even in the visible field. This is something you can observe by the aid of the nearby presented diagrams.
Spectroscopy thus, on the base of the black body diagram, assigns a temperature to the stars on the only basis of their colors.
With this prejudice, astronomers think that stars emit because they are incandescent. Is there any evidence supporting such affirmations? Not one. Stars emit colored radiations just because they are seen through many differently colored screens.
We know in fact that, on the Earth, there’s a vault filled with waters. Stars are biological amasses of bioluminescent critters living in the cosmic ocean. They keep on emitting light but they are cold. We can perceive them thanks to many amazing optical phenomena.