The moon illusion: I. How high is the sky?

Area of Science:

• Psychology
• Visual Perception
• Astronomy

Background:

• The moon illusion, where the moon appears larger near the horizon, is often explained by the flattened-dome hypothesis.
• This hypothesis suggests the sky is perceived as a flattened dome, altering perceived distance and size.

Purpose of the Study:

• To investigate the validity of the flattened-dome hypothesis as an explanation for the moon illusion.
• To test whether perceived distance to the sky changes with elevation and correlates with perceived moon size.

Main Methods:

• Experiment 1: Participants estimated the distance to the night sky at various elevations.
• Experiment 2: Participants estimated the distance to the sky around the horizon and correlated it with building distances.
• Control Experiment: Participants estimated the physical distances of horizon buildings.

Main Results:

• Perceived distance to the sky did not decrease with increasing elevation, contradicting the flattened-dome hypothesis.
• Sky distance estimates near the horizon correlated with physical building distances.
• Power functions described the relationship between estimated and physical distances, with different exponents for sky vs. building estimates.

Conclusions:

• The study's findings disconfirm theories attributing the moon illusion to a "sky illusion" like the flattened-dome hypothesis.
• The results indicate that perceived distance to the sky does not vary systematically with elevation in a way that explains the moon illusion.