A scale of seeing conditions, used by amateur astronomers, that describes the effect of atmospheric motions on an image, usually that of the Moon or a planet. Its categories are:

1. I perfect, without a quiver

2. II slight undulations, but with calm periods lasting several seconds

3. III moderate, with some greater air movements

4. IV poor, with the image in constant movement

5. V very bad, making observations very difficult

It was devised by E. M. Antoniadi.