Where does halo collide?

A halo is a ring or arc of light that appears around the sun or moon when their light is refracted and reflected by ice crystals suspended high in the atmosphere, the most common being a bright circle at about 22 degrees from the light source. Bravais's 1847 Mémoire sur les halos et les phénomènes optiques qui les accompagnent gave the earliest systematic study, working out the geometry of the ring from refraction through hexagonal ice prisms and reproducing the effect with a spinning glass prism. Greenler's 1980 Rainbows, Halos, and Glories collected the modern optics of the whole family of arcs. This referent is an optical event in the sky, measured by its angular radius, and it is not a disc of light painted around a saint's head, a bias in judgment, or an invisible envelope of matter around a galaxy.[1][2]

Unit

One optical ring or arc in the sky, described by its angular radius from the sun or moon

Recovery means

Not applicable

Measured by

Measured by the angular radius of the ring and by photometry of the arcs, and reproduced with prisms in the laboratory

The halo effect is a cognitive bias in which an overall impression of a person, or one salient positive trait, colors judgments of that person's other and unrelated qualities. Thorndike's 1920 A constant error in psychological ratings coined the term after finding that officers who rated a soldier highly on one attribute tended to rate that soldier highly on all others, as though a single halo spread across the ratings. Nisbett and Wilson's 1977 The halo effect: Evidence for unconscious alteration of judgments showed that people are often unaware the bias is operating. This referent is a measured error in human judgment, quantified by correlations among ratings, and it is unrelated to a ring of light in the sky, a golden disc in a painting, or a halo of dark matter.[3][4]

Unit

One rater's inflated agreement across traits traced to a single impression

Recovery means

Not applicable

Measured by

Detected by inter-trait rating correlations and by experiments that vary one salient attribute and measure the shift in unrelated judgments

A dark-matter halo is the massive, roughly spherical envelope of unseen matter that surrounds a galaxy and reaches well beyond its visible stars, dominating the galaxy's total mass and gravity. Ostriker and Peebles's 1973 A numerical study of the stability of flattened galaxies argued from simulations that a cold disc of stars cannot stay stable on its own and needs a massive surrounding halo to hold it together, an early quantitative case for the dark halo. This referent is an inferred gravitational structure, measured by its effect on rotation and dynamics, and it shares only the word with a ring around the moon, a saint's nimbus, or a bias in judgment.[5]

Unit

One galaxy's surrounding mass envelope, scaled by its total mass and radius

Recovery means

Not applicable

Measured by

Inferred from flat galaxy rotation curves, stellar velocity dispersions, gravitational lensing, and N-body stability simulations