Author Contributions
Conceptualisation, Y.T. and J.C.; methodology, Y.T., A.P. and S.T.; software, Y.T., A.P. and S.T.; validation, Y.T. and J.C.; formal analysis, Y.T.; investigation, Y.T. and J.C.; resources, Y.T.; data curation, Y.T.; writing—original draft preparation, Y.T.; writing—review and editing, Y.T., M.L., A.P., E.W. and J.C.; visualisation, Y.T. and J.C.; supervision, J.C. All authors have read and agreed to the published version of the manuscript.
Figure 1.
The MW observed under a rural sky in South Australia.
Figure 1.
The MW observed under a rural sky in South Australia.
Figure 2.
A 360 degree panoramic image covering the southern and northern celestial spheres of the MW created by joining multiple images. Photo: Courtesy of the European Southern Observatory (ESO) under Creative Commons Attribution-ShareAlike 4.0 International license.
Figure 2.
A 360 degree panoramic image covering the southern and northern celestial spheres of the MW created by joining multiple images. Photo: Courtesy of the European Southern Observatory (ESO) under Creative Commons Attribution-ShareAlike 4.0 International license.
Figure 3.
Simplified depiction of apposition (Left) and superposition (Right) compound eyes. The clear zone (cz) found in superposition eyes is labelled. Illustration adapted from [
11].
Figure 3.
Simplified depiction of apposition (Left) and superposition (Right) compound eyes. The clear zone (cz) found in superposition eyes is labelled. Illustration adapted from [
11].
Figure 4.
Stellarium location setting, Lincoln National Park, SA.
Figure 4.
Stellarium location setting, Lincoln National Park, SA.
Figure 5.
Left: Stellarium image (light pollution level: 1, MW brightness: 4, saturation: 1) with the azimuthal grid (green). Middle: Stellarium image (light pollution level: 1, MW brightness: 4, saturation: 1) with the celestial equatorial coordinate grid (blue). Right: Stellarium sky image (light pollution level: 5, MW brightness: 1, saturation: 1).
Figure 5.
Left: Stellarium image (light pollution level: 1, MW brightness: 4, saturation: 1) with the azimuthal grid (green). Middle: Stellarium image (light pollution level: 1, MW brightness: 4, saturation: 1) with the celestial equatorial coordinate grid (blue). Right: Stellarium sky image (light pollution level: 5, MW brightness: 1, saturation: 1).
Figure 6.
Bortle scale levels.
Figure 6.
Bortle scale levels.
Figure 7.
Flow chart for angle calculation steps from MW images.
Figure 7.
Flow chart for angle calculation steps from MW images.
Figure 8.
Thresholding method comparison for real sky images.
Figure 8.
Thresholding method comparison for real sky images.
Figure 9.
Left: RGB image. Middle: binary image. Right: edge image.
Figure 9.
Left: RGB image. Middle: binary image. Right: edge image.
Figure 10.
Test image from Stellarium with the following settings: location: SA, Australia, FOV: 120°, date: 1 February 2022, time: 02:30:17 (UTC+10:30).
Figure 10.
Test image from Stellarium with the following settings: location: SA, Australia, FOV: 120°, date: 1 February 2022, time: 02:30:17 (UTC+10:30).
Figure 11.
Projection integral in the direction, .
Figure 11.
Projection integral in the direction, .
Figure 12.
Radon transform, indicating the maximum value of .
Figure 12.
Radon transform, indicating the maximum value of .
Figure 13.
Left: angle calculation result for
Figure 10.
Right: angle result for rotation to vertical.
Figure 13.
Left: angle calculation result for
Figure 10.
Right: angle result for rotation to vertical.
Figure 14.
First column: In order to illustrate the results clearly, this column shows the MW with increased brightness (Stellarium MW brightness set as 5). 2nd–7th columns: Detection and angle calculation results for simulated sky images. The light pollution level for the test images is 3.
Figure 14.
First column: In order to illustrate the results clearly, this column shows the MW with increased brightness (Stellarium MW brightness set as 5). 2nd–7th columns: Detection and angle calculation results for simulated sky images. The light pollution level for the test images is 3.
Figure 15.
Top row: All Sky Camera images from Mount Burnett Observatory; bottom row: the simulated sky images with the increased brightness of MW area (Stellarium MW brightness set as 5).
Figure 15.
Top row: All Sky Camera images from Mount Burnett Observatory; bottom row: the simulated sky images with the increased brightness of MW area (Stellarium MW brightness set as 5).
Figure 16.
First column: Real sky images that are used for angle calculation test. 2nd–6th columns: Detection and angle calculation results for real sky images.
Figure 16.
First column: Real sky images that are used for angle calculation test. 2nd–6th columns: Detection and angle calculation results for real sky images.
Figure 17.
Moving angle calculation test images from Stellarium.
Figure 17.
Moving angle calculation test images from Stellarium.
Figure 18.
Moving angle calculation: Location: Melbourne Observatory (MELO), date: 27 February (start time 23:50). Location: Australia Astronomical observatory (AAO), dates: 25 May (start time 22:30), 1 July (start time 22:00).
Figure 18.
Moving angle calculation: Location: Melbourne Observatory (MELO), date: 27 February (start time 23:50). Location: Australia Astronomical observatory (AAO), dates: 25 May (start time 22:30), 1 July (start time 22:00).
Figure 19.
Comparison for the Canny and LRWEEDA edge detection methods that were tested on a full rotation circle of the test images from Stellarium with the following settings: Location: Australia Astronomical Observatory (AAO), date: 25 May (start time 22:30).
Figure 19.
Comparison for the Canny and LRWEEDA edge detection methods that were tested on a full rotation circle of the test images from Stellarium with the following settings: Location: Australia Astronomical Observatory (AAO), date: 25 May (start time 22:30).
Figure 20.
Comparison of the Canny and LRWEEDA edge detection methods tested on real sky images from the All Sky Camera, Mount Burnett, Australia.
Figure 20.
Comparison of the Canny and LRWEEDA edge detection methods tested on real sky images from the All Sky Camera, Mount Burnett, Australia.
Figure 21.
Comparison for the low-resolution images from Stellarium. Moving angle calculation: location: Melbourne Observatory (MELO), date: 27 February (start time 23:50).
Figure 21.
Comparison for the low-resolution images from Stellarium. Moving angle calculation: location: Melbourne Observatory (MELO), date: 27 February (start time 23:50).
Figure 22.
Comparison for the low-resolution images from Stellarium with pixel values for different resolution levels.
Figure 22.
Comparison for the low-resolution images from Stellarium with pixel values for different resolution levels.
Figure 23.
The MW area that was detected with light pollution levels set from 1 to 7 in Stellarium (date: 2 January 2022, time: 02:30 (UTC +10:30), location: SA, Australia).
Figure 23.
The MW area that was detected with light pollution levels set from 1 to 7 in Stellarium (date: 2 January 2022, time: 02:30 (UTC +10:30), location: SA, Australia).
Figure 24.
The MW area that was detected with light pollution Levels set from 1 to 7 in Stellarium (date: 2 May 2022, time: 02:30 (UTC +09:30), location: SA, Australia).
Figure 24.
The MW area that was detected with light pollution Levels set from 1 to 7 in Stellarium (date: 2 May 2022, time: 02:30 (UTC +09:30), location: SA, Australia).
Figure 25.
Moving angle calculation for light pollution is set as 4 and 6, location: Melbourne Observatory (MELO), date: 27 February (start time 23:50).
Figure 25.
Moving angle calculation for light pollution is set as 4 and 6, location: Melbourne Observatory (MELO), date: 27 February (start time 23:50).
Table 1.
Light pollution levels.
Table 1.
Light pollution levels.
Level | Title | SQM (mag/arcsec) | NELM |
---|
1 | Excellent dark sky site | 21.7–22.01 | 7.6–8.0 |
2 | Typical truly dark site | 21.5–21.7 | 7.1–7.5 |
3 | Rural sky | 21.3–21.5 | 6.6–7.0 |
4 | Rural/suburban transition | 20.4–21.3 | 6.1–6.5 |
5 | Suburban sky | 19.1–20.4 | 5.6–6.0 |
6 | Bright suburban sky | 18.0–19.1 | 5.1–5.5 |
7 | Suburban/urban transition | 18.0–19.1 | 5.0 at best |
8 | City sky | <18.0 | 4.5 at best |
9 | Inner City sky | <18.0 | 4.0 at best |
Table 2.
Night sky brightness values.
Table 2.
Night sky brightness values.
Condition | Illuminance (mlux) | Zenith Sky Luminance (mcd/m) | Zenith Radiance (mag/arcsec) |
---|
Overcast natural night | <0.6 | <0.2 | >21.8 |
Natural starlit night | 0.6–0.9 | 0.2–0.3 | 21.4–21.9 |
Bulge of the MW | N/A | 2.71 | 20.5–21.0 |
Rural night sky (clear, no moon) | 0.7–3 | 0.25–0.8 | 20.3–21.6 |
Rural night sky (overcast) | 0.7–9 | 0.25–0.7 | 19.0–21.6 |
Table 3.
Information about the All Sky Camera, Mount Burnett, Australia.
Table 3.
Information about the All Sky Camera, Mount Burnett, Australia.
All Sky Camera Information | |
---|
Location | Mount Burnett, Victoria, Australia |
Latitude | 37.9725 S |
Longitude | 145.4955 E |
Camera | ASI224MC |
Exposure | 30 s |
Computer | Raspberry Pi 3B+ |
Table 4.
Summary of results from the MW compass method and corresponding LP levels.
Table 4.
Summary of results from the MW compass method and corresponding LP levels.
Sequence | LP | Mean Error | Maximum Error |
---|
AAO 01 Jul | 4 | | |
AAO 25 May | 4 | | |
MELO 27 Feb | 4 | | |
MELO 27 Feb | 6 | | |