Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Moon Appearances
Name: Daniel
Status: student
Age: 15
Location: N/A
Country: N/A
Date: 1999 - 2000

Why does the moon appear large over the horizon, but small in the sky? What are the hypothesis that scientists come up with to answer this question?

First of all, the moon does not appear larger at the horizon than high in the sky. If you don't believe this, *measure* it with a protractor next time you have the opportunity.

What you are experiencing is an optical illusion. Why is the human brain subject to this one? Probably because we judge the size of objects by what is near them, the size of which we know. When you see the Moon high in the sky, nothing is near it, and you have no real clue to its size. Your brain assigns it a size based on some "default" distance at which it assumes faraway things lie, which is probably not much farther than your binocular vision is good for, about 20 to 40 feet. When the Moon is near the horizon, you see it next to mountains, trees, or buildings the size of which you know (or rather the visual processing part of your brain knows). Of course the Moon is bigger than they, and so the Moon suddenly looks much bigger.


Click here to return to the Astronomy Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (, or at Argonne's Educational Programs

Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory