What about the absent segments of the rainbow?

Do you know the composition of the sun?

Unfortunately, we can't physically travel to the scorching star to collect samples, like we did with the moon. However, there's a way to study its composition without venturing so far away. Instead of relying on a traditional rainbow, we use a more precise tool called a Fraunhofer spectrum, which consists of dark lines in the spectrum of light. These lines are akin to the mysterious dark marks observed in the spectra of stars, including our very own Sun. They appear because certain gas elements in the atmosphere selectively absorb the Sun's radiation at specific wavelengths. The first person to notice these lines was an English physicist named William Hyde Wollaston in 1802. However, it was the German physicist Joseph von Fraunhofer who made these lines famous by plotting over 500 of them and assigning some letters from A to G to the brightest ones. Even today, we use these letters to identify the lines. In our solar system, we've identified about 25,000 Fraunhofer lines.

Now, let's delve into the three main types of spectra. First, there's the continuous spectrum, which displays all the colors of the rainbow and all the wavelengths of visible light without any gaps. This occurs when white light is dispersed by a prism.

The second type is the emission spectrum, which is generated when atoms become excited and release light at specific wavelengths. Different elements have their unique signature wavelengths, creating distinct colors. For instance, sodium emits yellow light, neon gives off red and orange hues, and Mercury contributes blue and green wavelengths. These emission lines act like fingerprints for each element, allowing us to identify them.

Lastly, we have the absorption spectrum. In this scenario, when sunlight passes through a gas, certain colors are missing from the spectrum. This happens because atoms in the gas selectively absorb light at specific wavelengths, the same wavelengths they would emit if they were excited. As a result, we observe a continuous spectrum with black lines, which are caused by chemical elements in the Sun's outer layers absorbing specific wavelengths of light. By measuring the wavelengths of these lines and their intensities, we can determine the elements present and estimate their quantities. This method is akin to assembling a complex puzzle to decipher the Sun's composition.

Interestingly, in 1870, scientists discovered a set of lines, including a strong yellow one, that didn't match any known element. A scientist named Norman Lockyer proposed that this might be a new element, and he named it helium after the Sun deity Helios. Twenty-five years later, helium was indeed discovered on Earth.

This technique, known as spectroscopy, allows scientists to gather detailed information about materials both on Earth and in space by studying their colors. It relies on the relationship between light and matter, where different substances interact with light in distinct ways based on factors like temperature and composition.

Light, a form of electromagnetic radiation, behaves like a wave, with characteristics such as wavelength, which determines its color. Shorter wavelengths appear blue, while longer ones appear red. This property makes it possible to observe and measure the differences in wavelengths of light emitted or absorbed by various substances.

Spectroscopy involves separating light into its constituent colors, which can be done using tools like prisms or diffraction gratings. Spectroscopes and spectragraphs help scientists capture and measure these spectra. Spectra can be displayed as images, but to analyze the details, they are plotted on graphs. Spectrum graphs reveal variations in brightness and wavelength that may not be visible to the naked eye.

Spectra can be classified into different types based on how light and matter interact. The continuous spectrum is a smooth flow of colors without gaps and is used to determine surface temperature and other properties of objects, like stars.

The absorption spectrum appears as a continuous spectrum with certain colors dimmed or missing. These missing colors are absorption lines, which result from starlight passing through materials like dense gases that absorb specific wavelengths. Each element in the gas has its unique absorption pattern, allowing for the identification of elements and compounds and the estimation of their quantities, as well as information about the temperature and density of the gas.

In summary, spectroscopy is a powerful technique that helps us understand the composition and properties of celestial objects, including the Sun, by analyzing the patterns of light they emit or absorb. It is a crucial tool for studying the cosmos and the materials within it.