by alter-ego » Tue Dec 29, 2020 2:50 am
Chris Peterson wrote: ↑Sun Dec 20, 2020 3:55 am
alter-ego wrote: ↑Sun Dec 20, 2020 3:39 am
Chris Peterson wrote: ↑Sat Dec 19, 2020 7:32 pm
But you did need the date to narrow it down. And a degree of luck. Plenty of opportunities for ambiguities in an image of Jupiter with two moons showing.
Nope. I knew nothing a priori - neither date, time nor location. Simply put, it was educated trial and error. The only the 16th works to locate the moon, and, though not necessary, identifying HIP 98575 helped fine tune the time for Jovian moon certainty. For fun, I roughed in a location to match the image. This is a challenge because I have to assume camera orientation.
Location is irrelevant. But you depend upon more information than just Jupiter and two moons in an image, for which there are an infinite number of possible times, all the more given that you can't reliably identify which of the four Galilean moons make up the two dots.
Certainly there are images for which what you say is true. However, this particular image has enough analyzable information to not only reliably identify the Callisto as the second moon, but also identify a 2000km path within which the image could have been taken over roughly a 10-minute time window.
- Only looking at Jupiter and the two moons, it can be determined that Callisto is the only solution for the second moon:
→ A measured 8.4' separation between the two moons corresponds to an Image time ~12/16 23:30 UT
→ Moon's separation =97% of the maximum possible. Of the 4 Jovian moons, Callisto and Ganymede are the only pair that reach separation.
- Identifying Dec 16th UT as the day is determined from the moon position wrt the planet
- Comparing the plot of Jovian moons orbital positions over time against the measured 8.4-arcmin separation between Ganymede and the second moon in the image, it's readily apparent that Callisto must the moon
→ Given the measured 50% diameter of Jupiter's over-exposed disk ≈ 2.7' (5x larger than actual size), the plot shows the inner moons, Io and Europa, are essentially buried by Jupiter's oversized disk when the image was captured.
→ Given 1) A reasonable image measurement accuracy of 1', and 2)That either Io and Europa would be visible if they were located far enough outside of Jupiter's glare (Callisto is the faintest of the 4 main Jovian moons), I estimate that the capture-time window ≥10 hours that the inner moons would not be visible.
There is no doubt in my mind that Callisto is the only reasonable candidate for the second moon.
Lacking observer location and image details, this method is the easiest and most direct approach to establishing Callisto is the moon in question. Even the large, 10-hr uncertainty in the capture time does not change the answer.
- To predict observer locations, I did a another, totally independent (and more tedious), analysis to also find the image-capture time:
For many input image-times, the closest observer locations (Lat & Long) were empirically solved such that, as viewed from each location, the Moon at the same apparent RA & Dec as in the image (I used identifiable stars in the image to more accurately determine the imaged lunar coordinates, and thus observer locations) The results:
- A 2000-km path cutting across South America (Argentina) where twilight conditions existed, as well as an image-capture window of ~10 minutes, and
- Best estimate solution time ~ 12/16/23:53UT
→ Regarding location on Earth, it is irrelevant wrt Jovian moon positions and timings. However, when extracting an observation time from the apparent lunar RA & Dec, observer locations are relevant. The primary reason why there's a locus, instead of a single-point location, is because the image did not have a horizon reference. The specific time shown assumes a horizon parallel to the horizontal image frame edge.
I was quite surprised by only a ½-hour difference in image-time. Even though much more tedious, the more involved location search method resulted in a much smaller image-capture time uncertainty.
[color=#000000][/color][quote="Chris Peterson" post_id=309105 time=1608436535 user_id=117706]
[quote=alter-ego post_id=309104 time=1608435558 user_id=125299]
[quote="Chris Peterson" post_id=309100 time=1608406328 user_id=117706]
But you did need the date to narrow it down. And a degree of luck. Plenty of opportunities for ambiguities in an image of Jupiter with two moons showing.
[/quote]
Nope. I knew nothing a priori - neither date, time nor location. Simply put, it was educated trial and error. The only the 16th works to locate the moon, and, though not necessary, identifying HIP 98575 helped fine tune the time for Jovian moon certainty. For fun, I roughed in a location to match the image. This is a challenge because I have to assume camera orientation.
[/quote]
Location is irrelevant. But you depend upon more information than just Jupiter and two moons in an image, for which there are an infinite number of possible times, all the more given that you can't reliably identify which of the four Galilean moons make up the two dots.
[/quote]
Certainly there are images for which what you say is true. However, this particular image has enough analyzable information to not only reliably identify the Callisto as the second moon, but also identify a 2000km path within which the image could have been taken over roughly a 10-minute time window.
[list=1][*][color=#0000FF][b][i]Only looking at Jupiter and the two moons, it can be determined that Callisto is the only solution for the second moon:[/b][/color][/i]
→ A measured 8.4' separation between the two moons corresponds to an Image time ~12/16 23:30 UT
→ Moon's separation =97% of the maximum possible. Of the 4 Jovian moons, [u]Callisto and Ganymede are the only pair that reach separation[/u].
[list=•][*]Identifying Dec 16th UT as the day is determined from the moon position wrt the planet[*]Comparing the plot of Jovian moons orbital positions over time against the measured 8.4-arcmin separation between Ganymede and the second moon in the image, it's readily apparent that [u]Callisto must the moon[/u][/list]
[float=left][img3=]https://lh3.googleusercontent.com/yow17jKxVX47JQME949KFVxvQeQQGdzbabpIVR9XBzKzgjmHAHYs2risalkfajfhNrupz7rMM661s-slpDSCJjFoIFSGZMpTAcauhfw2lFTw3A-LdHn_yk8eilNSoOsZkA0tEY5xWABPQFTQglDriM71gkGLl3UXZwjLn255Sck_2jPb08aTzoRxlCsj9eyYPMZKGTFY1tLwC1TOGdKyWUoIISZRa-b5UtoV_pv4x2yKZint6lnodFojPVpqebBgINRn4ZX5y5YRRkO_t9lhwsqJKXY-Juk6wCoHRg6pV4qx7fXFHKjcsOo3xLC2Ll1Kgt0sYGcVpKxYxZw0o62sxZvHd03TitcSho7ccESPkoNxsCV5uLV3wSecDES4w7Nwv6pXXQ0g9DSuSUh4exyqq8xRhXMr3gsUZ4YPB9vlksiV9a2TMse9RCj5BMwZDFIlj53GEGiRB36wp-kzIQddTUCSzkTa3wIhE8m0Lc1Y2tG9JkIegcAeW5z0sl9SawBHg-e7zKXG4RQ2Y4HtBXacwX4wraWjtjBg-n43mdI8ewiVunWMiyossP8jV0sIs8HA1aZ3Wv-_ZV4vkPEphsScIJrOfHHIRVCw2Eitu8qO0Gjok6CuK1I-p6zwqq1TCBgw3sMlZUqK2WIR3py26_f7m2n6-kXXPR539tiBUFy4TqNMmyI9qUL2SoB753Kz=w837-h588-no?authuser=0[/img3][/float] → Given the measured 50% diameter of Jupiter's over-exposed disk ≈ 2.7' (5x larger than actual size), the plot shows the inner moons, Io and Europa, are essentially buried by Jupiter's oversized disk when the image was captured.
→ Given 1) A reasonable image measurement accuracy of 1', and 2)That either Io and Europa would be visible if they were located far enough outside of Jupiter's glare (Callisto is the faintest of the 4 main Jovian moons), I estimate that the capture-time window ≥10 hours that the inner moons would not be visible.
[color=#0000FF][b]There is no doubt in my mind that Callisto is the only reasonable candidate for the second moon.[/b][/color]
Lacking observer location and image details, this method is the easiest and most direct approach to establishing Callisto is the moon in question. Even the large, [u]10-hr uncertainty in the capture time does not change the answer[/u].
[*][i]To predict observer locations, I did a another, totally independent (and more tedious), analysis to also find the image-capture time:[/i]
For many input image-times, the closest observer locations (Lat & Long) were empirically solved such that, as viewed from each location, the Moon at the same apparent RA & Dec as in the image (I used identifiable stars in the image to more accurately determine the imaged lunar coordinates, and thus observer locations) The results:
[list=•][*]A 2000-km path cutting across South America (Argentina) where twilight conditions existed, as well as an image-capture window of ~10 minutes, and[*]Best estimate solution time ~ 12/16/23:53UT[/list]
[float=left][img3=]https://lh3.googleusercontent.com/TbniOPn1VF0vv0eHcEDO9MakLbl75-Y7o3aWzKXSaFJRKsbHjKa7HhQ0pqPKKxkkiU-U6c2x_5cy8uyaRDFXjCXWgfQ9cKpfhhOmh9OhYTuhtGjAJcIL2q_H6GHUTv-RANYjklMp0PHAuOeOKRSW9pa57uG_KxSvCrtxxvDJ9L_T1CEU7lUK7c7cp5MZ4nBoyx_vzhnE8X-fRmLuX0YuckrgRslOmdRmPa7noIAlcQswb31ohnnrXUoDAp0_Co00WDAjytycikmKRIFq6Ra6VKufeHjJT6vjJ_XW1Sk_EYoSeh3C6qn9qaGVGF3QYo44qIbl6eYwETft_xKv3xuNR3HlPTPhbCiAZS-OSiAOboyFCa5rb4OTi2rgxn7heDDtBhaJ34g-vFZmrkAfTviWDuMrnJ9hFgYuA4oFTr9r2OF8o7NFMk-I1kTyWiKyJpeGX-GDfoX-RpEZav9ccnHFup8NcgwXZJ64QKXUmLnLZsywlJi2OANxnk8KVtWuKlV-ir9pme6wS3wvnfIuGWRboM6d8cWL-C2Aj_wboFYESWhNAWd4yeZn6EJ2APOXl_HWinhTZdG9FFFeUIC9I-tO-kvMDmKR-UAxWGptgiAvYRN05EFJajReKJoIcYLts03k7U1zKfOuC6cBXG2MinEiEPrSJveeQsHloqO-Dkqr-re3wXy10vyG0FsF1-9V=w753-h519-no?authuser=0[/img3][/float]
→ Regarding location on Earth, it is irrelevant wrt Jovian moon positions and timings. However, when extracting an observation time from the apparent lunar RA & Dec, observer locations are relevant. The primary reason why there's a locus, instead of a single-point location, is because the image did not have a horizon reference. The specific time shown assumes a horizon parallel to the horizontal image frame edge.
I was quite surprised by only a [size=130]½[/size]-hour difference in image-time. Even though much more tedious, the more involved location search method resulted in a much smaller image-capture time uncertainty.