astronomy Astronomy is a natural science that studies celestial objects and the phenomena that occur in the cosmos. It uses mathematics, physics, and chemistry in order to explain their origin and their overall evolution. Objects of interest includ ...

, dropout is a

radiation In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or a material medium. This includes: * ''electromagnetic radiation'' consisting of photons, such as radio waves, microwaves, infr ...

source whose radiation intensity falls off sharply below a specific

wavelength In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats. In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...

. The source will be easily visible when its light is filtered to wavelengths longer than the cutoff value, but will "drop out" of the image when it is filtered to wavelengths shorter than the threshold. This is a standard method for locating distant galaxies in deep field images. Because the

hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

that surrounds the galaxies absorbs light with a wavelength around 100 nanometers, the galaxies have a natural dropout threshold. The exact wavelength of this threshold is

redshift In physics, a redshift is an increase in the wavelength, and corresponding decrease in the frequency and photon energy, of electromagnetic radiation (such as light). The opposite change, a decrease in wavelength and increase in frequency and e ...

ed and can be used to determine the distance to the galaxy.

References

Extragalactic astronomy {{physical-cosmology-stub

See also

References