"Parallax" is a seemingly obscure trigonometric concept that astronomers use to measure distances to nearby stars, but it derives from an earthly optical phenomenon that is easily grasped. The operative principle is that the location of nearby objects will appear different against a distant background when the position of the observer changes. In Lestrygonians Bloom thinks of it as a "Greek" word that "I never exactly understood," comparable to "metempsychosis." In this hellenic book, both terms promise to hold multiple applications to ordinary life, just as the adventures of Odysseus do.

JH 2016

Parallax as demonstrated by closing first one eye and then the other. Source: quillandpad.com.

Parallax as demonstrated by looking out the window of an automobile at two different points on the road. Source: www.eg.bucknell.edu.

Parallax as demonstrated by looking at a star in January and July. Source: hyperphysics.phy-astr.gsu.edu.

The parallax angle (p) used to calculate distance (d). Source: www.atnf.csiro.au.

Degrees of difference in parallax angles seen in relation to different distances. Source: csep10.phys.utk.edu.