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As for the title. Although the scenic Blue Moon Jupiter Saturn combo of last week end wasn't really suitable for shooting with a G-cam in Astrophotography mode, I've nevertheless tried to see if I could have got more stars.

Just after the shooting I was astonished to see that even Jupiter lead to a reflection on the sea surface (no boats or lights were there!).

Later, a friend suggested that the reflection is an up side down ghost of the Moon's one. It seems so, as many features correspond, and one can see a cross shape formed by the little waves breaking on the shore.

I think that experienced photographers here can easily confirm this hypothesis or convertely push back to the astonishing Jupiter reflection (the astrophotography mode of G-cams is, among other things, a kind of long exposure).

Taken by Parrot gcam in astro mode with a redmi note 8t smartphone, compressed

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  • \$\begingroup\$ When I saw this question in the "Hot Network Questions" sidebar, I thought at first it might be on the skeptics.stackexchange.com site. \$\endgroup\$ Aug 25, 2021 at 15:22
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    \$\begingroup\$ @MarkStewart :)) click baiting not intended :))) \$\endgroup\$
    – Alchimista
    Aug 25, 2021 at 15:24

2 Answers 2

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The green streak in "Jupiter's reflection" makes it much more likely to be caused by a passing boat (going from left to right given the color):

enter image description here

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  • \$\begingroup\$ That would be the most straightforward answer. But as I have noticed the strike immediately after shooting there were no not boats around. Still, as I am from a sea town, this should be. I will check the entire sequence and come back to accept. For the moment just upvote as the answer totally makes sense. \$\endgroup\$
    – Alchimista
    Aug 25, 2021 at 8:55
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    \$\begingroup\$ @Alchimista: The boat might have been just a tiny moving point of light on the horizon, easily overlooked. It only looks so prominent in the photo because of the long exposure spreading it out and brightening what would otherwise have been a fairly dark scene. (Note that the Moon and its reflection, which would likely have been the brightest things in the actual scene, are almost completely saturated in the photo and so look relatively less bright compared to other lights in the image.) \$\endgroup\$ Aug 25, 2021 at 12:30
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    \$\begingroup\$ @IlmariKaronen yes, and anyway the colours fits with a boat. Accepted. I overlooked the colours pointing to a boat moving to the right indeed. \$\endgroup\$
    – Alchimista
    Aug 25, 2021 at 15:21
  • \$\begingroup\$ Are you saying you think the green streak is caused by a vessel, but the whitish reflection above and below it are caused by something else? Or that both the green streak along with the whitish reflection are both caused by a vessel? \$\endgroup\$ Aug 26, 2021 at 12:11
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    \$\begingroup\$ It looks like both the green streak and the white streak immediately above are some other light source (likely the surmised boat). The white streak in particular distinctly appears to be a source rather than a reflection, as it looks quite different from the top of the moon's reflection. It also appears much wider than Jupiter; more so, proportionally, than the Moon's reflection. It's also not quite centered. All of which points to a) a boat, and b) an unusual coincidence that the boat is almost directly below Jupiter. \$\endgroup\$
    – Matthew
    Aug 26, 2021 at 13:02
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While the reflection in your picture is probably not Jupiter's (see xenoid's answer), it is totally possible for stars and planets to be reflected off water, either as streaks like here or (if the water is still enough) as points.

Here's a nice example photo by Phil Plait (of Bad Astronomy fame) showing a conjunction of Venus and Jupiter, with both reflected off a lake:

Venus and Jupiter reflected off a lake (photo by Phil Plate, CC-By-SA 2.0)
(Photo © Phil Plait 2019, used under the CC-By-SA 2.0 license. See also original on Flickr and some context here.)

As can be seen in this photo, however, the reflections of stars or planets are not significantly wider or brighter than the actual star or planet itself. Of course, the actual brightness of a saturated point of light is hard to estimate from a photo, but it seems unlikely that the wide bridge of light in your photo could be a reflection of the small point that is Jupiter.

(Nor is it likely to be a ghost of the Moon's reflection, since there's no obvious optical mechanism that could produce such a ghost and make it line up perfectly with the horizon. It seems most likely to me that xenoid's explanation is right, and there in fact was a boat coincidentally passing through the scene when you took the image, and that its lights — smeared horizontally by the boat's movement during the long exposure — generated the reflection seen in your photo.)

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    \$\begingroup\$ Indeed. Jupiter is bright enough to cast shadows, BTW. discovermagazine.com/the-sciences/… \$\endgroup\$ Aug 26, 2021 at 8:46
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    \$\begingroup\$ @EricDuminil thanks. I have accepted the other answer as it must be the right one to the question as I have posed it... But this answer and your comment are well fitting the underlying question "do planets cast reflection?“. Upvoted both. \$\endgroup\$
    – Alchimista
    Aug 27, 2021 at 8:50

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