At the time of its discovery, it was the galaxy with the lowest known surface brightness, Σ 26.8mags arcsec, and the faintest galaxy known from its intrinsic absolute brightness.

Its companion is a type F4 star of apparent brightness 5.2 and absolute brightness 3.5, designated alpha-1 Librae (α1 Lib).

But Hubble could not have done this without Harlow Shapley's earlier calibration of the absolute brightnesses of these key lighthouses.

Absolute magnitude is a measure of a star's absolute brightness.

Eigengrau is perceived as lighter than a black object in normal lighting conditions, because contrast is more important to the visual system than absolute brightness.

Astronomers have long established a correlation between the pulsations of these stars and their absolute brightness.

Like many of the author's works, the title story is set at an astronomical observatory and refers to a star's absolute brightness, connecting that phenomenon with the relationship between two individuals in the story.

Since this absolute brightness is supposedly known, the measured brightness (or degree of dimming) of a Cepheid as seen from Earth affords an estimate of its distance.

They found that when the luminosity, or absolute brightness, of a star is compared with its color, the star usually fits into a simple graphic pattern now called the Hertzsprung-Russell Diagram.

The period of these fluctuations varies inversely with luminosity, or absolute brightness.