parallax

Everyday

The way an object seems to move against a far background when you look at it from two different places, such as with one eye and then the other. tree →

In the lessons

In science lessons parallax explains why a nearby thing jumps when you close each eye in turn, and astronomers use it to measure how far away stars are. In maths and science it is also why you must read a ruler or measuring jug with your eye straight in front, to avoid «parallax error». Phrases: «parallax error».

Examples

• Hold up your thumb and close one eye, then the other — that jump is parallax. tree →
• Read the measuring cylinder at eye level to avoid parallax error. tree →
• Astronomers use parallax to measure distances to stars. tree →
• Video games use parallax to make backgrounds look far away. tree →
• Parallax helps our two eyes judge depth. tree →

Note

Uncountable. Stress: PA-ra-lax. In measuring: look straight at the scale or your reading may be wrong.