File:Twilight illumination by sun depression luxes 1 r 1.svg
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Captions
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Summary[edit]
| Description |
English: Outdoor illumination of twilight, by altitude on sun. Angle of sun altitude in degrees, illumination in luxes (lx). |
| Date | |
| Source | Own work |
| Author | Merikanto |
Source of equations is
https://www.hnsky.org/sqm_twilight.htm The brightness (SQM) value of the twilight sky NSSKY planetarium program
Python 3 source code
-
- illumination of twilight
- luxes from sun altitude
- sun altitude between -18 ... 0
- 15.8.2023 0000.0000
import math
import numpy as np
import matplotlib.pyplot as plt
- The brightness (SQM) value of the twilight sky
- estimation of illumination grom threshold magnitude
def calculate_illum_from_alt(alt1):
sqm1=999
if(alt1<0):sqm1=-1.057*alt1+6.7489
if(alt1<-12):sqm1= -0.0744*alt1*alt1-2.5768*alt1-0.5845
if(alt1<-18):sqm1=-999
sqm0=-1.057*0+6.7489
sqm6=-1.057*-6+6.7489
deltasqm1=sqm0-sqm1
deltalog1=deltasqm1*0.4
illumcoeff1=math.pow(10,deltalog1)
illum1=illumcoeff1*450 ## assumed sunset 435 lx
return(illum1)
def np_calculate_log_illum_from_alt(alts1):
sqm1=999
#if(alt1<0):sqm1=-1.057*alt1+6.7489
#if(alt1<-12):sqm1= -0.0744*alt1*alt1-2.5768*alt1-0.5845
#if(alt1<-18):sqm1=-999
sqm1=np.copy(alts1)
sqm2=np.copy(sqm1)
sqm1=np.where(sqm1>-12,-1.057*sqm1+6.7489, 0)
sqm2=np.where(sqm2<-12.001, -0.0744*sqm2*sqm2-2.5768*sqm2-0.5845,0)
sqm1=sqm1+sqm2
sqm0=-1.057*0+6.7489
sqm6=-1.057*-6+6.7489
deltasqm1=sqm0-sqm1
deltalog1=deltasqm1*0.4
illumcoeff1=np.power(10,deltalog1)
illum1=illumcoeff1*450 ## assumed sunset 435 lx
logillum1=np.log10(illum1)
return(logillum1)
alt1=-7
illum1=calculate_illum_from_alt(alt1)
print(alt1, illum1)
alts1=np.linspace(-18,0,180)
logillums1=np_calculate_log_illum_from_alt(alts1)
- print (illums1)
plt.xlabel("Altitude of Sun, degrees", size=18)
plt.ylabel("Log10 of illumination lx", size=18)
plt.yticks(fontsize=18)
plt.xticks(fontsize=18)
plt.title("Illumination of twilight, luxes", fontsize=22)
plt.plot(alts1, logillums1, linewidth=6, color="#ff7f00")
plt.grid()
plt.axvline(x = 0, color = '#FFFF00', label = 'Sunset')
plt.axvline(x = -6, color = '#7f7f00', label = 'Civil twilight ends')
plt.axvline(x = -12, color = '#3f3f00', label = 'Nautical twilight ends')
plt.axvline(x = -18, color = '#1f1f00', label = 'Astronomical twilight ends')
plt.text(-5, 0, "Civil twilight", size=17)
plt.text(-11.5, -1, "Nautical twilight", size=17)
plt.text(-17.5, -2, "Astronomical twi.", size=17)
plt.show()
Licensing[edit]
- You are free:
- to share – to copy, distribute and transmit the work
- to remix – to adapt the work
- Under the following conditions:
- attribution – You must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use.
- share alike – If you remix, transform, or build upon the material, you must distribute your contributions under the same or compatible license as the original.
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| Date/Time | Thumbnail | Dimensions | User | Comment | |
|---|---|---|---|---|---|
| current | 12:21, 15 August 2023 | | 902 × 616 (34 KB) | Merikanto (talk | contribs) | Uploaded own work with UploadWizard |
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