2.1 Getting accurate readings
Nobody has performed the task of defining a relationship between the two methods of sky brightness (
x
magnitude
skies and magnitudes per square arcsecond) -- probably because one is subjective and the other is objective and a wide
variety of people would have to be polled.
An approximation exists for the conversion between NELM and MPSAS. You can use an NELM converter[5] created
by SQM user K. Fisher to do that conversion, or the chart shown in Figure 2.2 and Equations (2.2) and (2.3).
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”:
Unihedron SQM-LU-DL-V Operator’s Manual -
20211013
17
Summary of Contents for SQM-LU-DL-V
Page 2: ......
Page 104: ...14 Glossary 104 Unihedron SQM LU DL V Operator s Manual 20211013...
