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HST images of Uranus and Neptune
titanicrivers
post Feb 14 2019, 09:16 PM
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Amazing new images from Hubble Space Telescope (HST) of Uranus and Neptune! https://earthsky.org/space/hubble-space-tel...-uranus-neptune
Here are the Hubble site images: http://hubblesite.org/images/news/release/2019-06
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antipode
post Feb 15 2019, 06:56 AM
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Uranus especially continues to surprise - Voyager IIs flyby timing and its camera's filterset certainly misled people about how dynamic its atmosphere can be.
In the continuing absence of the followup probes the two ice giants so badly deserve, I look forward to what the ELTs and next gen adaptive optics will achieve.
GMT arrival = 6 years with any luck.

P

Actually, considering the large portion of the visible globe of Uranus covered by that seemingly bright cloud (I presume this is a near IR image), has it had any
effect on the planet's magnitude in the visible?
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dolphin
post Feb 17 2019, 06:30 AM
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QUOTE (antipode @ Feb 15 2019, 07:56 AM) *
Uranus especially continues to surprise - Voyager IIs flyby timing and its camera's filterset certainly misled people about how dynamic its atmosphere can be.
In the continuing absence of the followup probes the two ice giants so badly deserve, I look forward to what the ELTs and next gen adaptive optics will achieve.
GMT arrival = 6 years with any luck.

P

Actually, considering the large portion of the visible globe of Uranus covered by that seemingly bright cloud (I presume this is a near IR image), has it had any
effect on the planet's magnitude in the visible?



That was my question. Does Uranus have such complexity in the visible range? If so, that would be markedly different from the uniformity we saw during the Voyager flyby.
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JRehling
post Feb 18 2019, 06:26 PM
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QUOTE (dolphin @ Feb 16 2019, 11:30 PM) *
That was my question. Does Uranus have such complexity in the visible range? If so, that would be markedly different from the uniformity we saw during the Voyager flyby.


I think Uranus may have been cheated a bit by the design decisions of Voyager.

The color filters on the Voyager cameras are described in wonderful detail here:
http://www.planetary.org/multimedia/space-...r_response.html

There was no red. The orange filter zeroed out at 650 nm, with a peak around 580nm.

I've taken many multispectral photos of Uranus including B, G, R, and near IR. I can expect easily to resolve the polar hood if nothing else. It is blank as can be in B and G, but the polar hood is easily visible in IR (>685 nm) and dimly in R (595 – 680 nm).

It's a near certitude that an orange filter missed out on a lot of the needed sensitivity for seeing this feature, if it were the same in 1986 as it has been 2016-2018.
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JRehling
post Feb 18 2019, 07:38 PM
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Here are pictures I personally took with a 235mm Schmidt–Cassegrain and the aforementioned filters on October 18, 2018. The contrast is evident in the IR image, discernible but subtle in R, and completely absent in the G+B (it is absent in both of those, of course, for it to be absent in the sum of them).

At right is a composite where I used the luminance of the IR image, then colored it with the RGB image but with the red plane doubled. It's a nice appearance, but a bit past the bounds of "true color." The fact that both the hue and the brightness of the cap are different from the rest of the planet speaks to the fact that both IR and R show the hood.

There is also a thin equatorial belt that other observers captured but I did not.

But green does not. So we should expect the Voyager camera, were it taking an image of Uranus today, to turn up something blank because of the lack of a proper red filter.
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