In smaller scales, parallax is used directly to find the distance of celestial bodies (stars) from Earth (geocentric parallax) and from the Sun (heliocentric parallax). Visible light is used in parallax measurements. Parallax is effective over relatively small scales.
However, observing galaxies as old as the universe involves much larger scales, and visible light cannot reach us beyond a certain distance. This is because the shorter wavelengths of visible light are scattered by dust, vapor, and gases. Therefore, infrared signals with longer wavelengths are used to observe distant objects such as ancient galaxies. The longer wavelengths of infrared signals can penetrate dusty or gaseous environments.
The James Webb Space Telescope (JWST) uses near-infrared and mid-infrared cameras to observe very distant galaxies.
The above image shows the respective distances corresponding to the increased wavelengths of infrared signals, helping to determine the distances of galaxies based on the wavelengths of the signals received. Additionally, the expansion of space increases these wavelengths further, in addition to the normal increment with light-travelled distance.
Furthermore, by analysing these signals using a spectrograph—an instrument that disperses electromagnetic radiation into a spectrum and photographs or maps it—we can understand the composition of the observed object. The spectrograph converts signals according to their frequencies and corresponding wavelengths.
Therefore, by measuring the wavelengths of these signals, the distance to the object can be determined, not by using the parallax of visible light but by using infrared.
#InfraredSignals #JWST #JamesWebbSpaceTelescope #Spectrograph #GalacticDistances
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