Brightness scale
(Section 2.6.3.3.2)The brightness of noctilucent clouds can be estimated according to the five-point scale given in Table 11.
Table 11. Scale for the brightness of noctilucent clouds
|
Scale |
Description |
|
1 |
Very weak noctilucent clouds, barely visible against the background of the twilight sky; detected only through very careful examination of the sky |
|
2 |
Noctilucent clouds easily detected, but having low brightness |
|
3 |
Noctilucent clouds clearly visible, standing out sharply against the twilight sky |
|
4 |
Noctilucent clouds very bright, attracting the attention of casual observers |
|
5 |
Noctilucent clouds extremely bright and noticeably illuminating objects facing them |
The forms of noctilucent clouds are classified as follows.