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Blues

Main articles: Radiation astronomy/Blues and Blue astronomy

This picture from the Voyager 2 sequence shows two of the four cloud features which have been tracked by the Voyager cameras during the past two months. Credit: NASA.

Blue astronomy is focused on the wavelength range 450-475 nm.

Stars are often referred to by their predominant color. For example, blue stragglers are found among the galactic halo globular clusters. Blue main sequence stars that are metal poor ([Fe/H] ≤ -1.0) are most likely very different in origin from blue stragglers.

"[G]round-based UV [and blue astronomy] is a powerful facility for [the] study of [the] chemical evolution of [the] early Galaxy." UV and B astronomy use radiation over the wavelength range 355.0-500.0 nm.

“To date, all of the reported hypervelocity stars (HVSs), which are believed to be ejected from the Galactic center, are blue and therefore almost certainly young.”

A trace amount of methane is also present. Prominent absorption bands of methane occur at wavelengths above 600 nm, in the red and infrared portion of the spectrum. As with Uranus, this absorption of red light by the atmospheric methane is part of what gives Neptune its blue hue, although Neptune's vivid azure differs from Uranus's milder cyan. Since Neptune's atmospheric methane content is similar to that of Uranus, some unknown atmospheric constituent is thought to contribute to Neptune's colour.