We call the distribution of electromagnetic waves at various wavelengths a spectrum. The rainbow made when sunlight passes through a prism is the spectrum of visible light. It is classified as a continuum spectrum because it has a broad wavelength range.
However, looking closely at the solar spectrum, we can find several dark lines cutting into the spectrum which appeared continuous. These are called absorption lines. These appear because the atoms and molecules comprising the Sun’s atmosphere absorb part of the light emitted as a continuum spectrum from the surface of the Sun. Based on their species and state, the atoms and molecules absorb electromagnetic radiation at characteristic wavelengths. Together these absorption lines corresponding to the various characteristic wavelengths are called a line spectrum.
The wavelengths of the absorption lines found through spectral analysis can reveal what kinds of materials a star is made from, even when the star is so distant that even seen through a telescope it appears as nothing more than a point of light. Moreover, by measuring the Doppler Effect exhibited by the wavelengths of the absorption lines, it is even possible to know the velocity and motion of the star. Various messages from stars are contained in the spectrum.image credit：Hida Observatory, Kyoto University / PaoDST WG, PAONET

SXDF-NB1006-2, discovered by the Subaru Telescope, is one of the most distant galaxies ever observed. The faint light of the spectral line emitted by hydrogen atoms arriving at the Earth from 129.1 billion light-years away was observed in the near infrared.
However, it is known that this spectral line originated as ultraviolet rays with a wavelength of 121.6 nanometers. Why was a spectral line emitted with a wavelength in the ultraviolet region observed as near infrared?
The reason is that the expansion of the Universe has been continuing since the Big Bang. Because the space the electromagnetic wave is traveling through is itself expanding, the wavelength of the electromagnetic wave is also stretched. This is called red shift. It is found that the more distant the origin of the electromagnetic wave, the larger the effect of red shift is.
Actually, the distance to SXDF-NB1006-2 was calculated by using this red shift. By calculating how much the spectral line has stretched from the original wavelength, the distance the electromagnetic wave has traveled, in other words the distance to the object, can be estimated. image credit：NAOJ

Each species of atom or molecule contained in the gas floating in space emits electromagnetic waves at characteristic wavelengths. These are called emission lines, and it is known that various molecules emit electromagnetic waves with radio wave wavelengths.
For instance, carbon monoxide emits radio waves of 2.6 millimeter wavelength, and by detecting these we can see the distribution of molecular clouds that cannot be observed at other wavelengths. A molecular cloud is a region of dense gas consisting mainly of molecular hydrogen. Stars are born from these collections of gas.
Various other emission lines are also detected in the molecular clouds. By investigating what molecules emit emission lines at which wavelengths in laboratory experiments on Earth, we can determine the molecules which exist in the distant Universe. Now, various molecules, such as ammonia and methanol, have been discovered through observations.
ALMA is able to detect amino acids, which are the material for life, with high sensitivity. If we find that amino acids are created at the sites of planet formation, new discoveries about the relationship between life and the Universe will be possible.