Unihedron SQM-LU, Operator'S Manual

Page: 13 / 67

2.1 Getting accurate readings
Figure 2.2: Mpsas vs NELM
Convert NELM (V mags) to MPSAS (B) sky brightness [3]
B
mpsas
= 21 . 58
−
5
×
log (10
(1 . 586 − N ELM/ 5)
−
1) (2.2)
Convert MPSAS (B) sky brightness to NELM (V mags) [4]
N ELM = 7 . 93
−
5
×
log (10
(4 . 316 − ( Bmpsas/ 5))
+ 1) (2.3)
NSU
A newly proposed term to define “Natural Sky Units”:
In “natural sky units” (radiance relative to an assumed natural radiance of 21.6 magSQM/arcsec
2
, see
methods), the range was 0.22 - 2200 NSU. Before the introduction of anthropogenic light, the radiance of a
patch of sky near zenith on moon-free nights is likely to have been nearly always within the range 21 (galactic
center near zenith) to 24 mag/arcsec2 (very thick clouds), or 0.1 - 1.7 NSU.[1]
Unihedron SQM-LU Operator’s Manual -
20170728
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