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I recall this very point coming up at a lecture at last year’s Winchester weekend. Of course, it is well known that these camera images are enhanced. And some quite odd-looking colours can result from the combination of certain narrowband filters. Because news media are often uncritical, enhanced images can easily appear in print or on websites without any technical explanation of which filters have been combined. And members of the public think that the planet really looks like that. Sometimes the eyepiece view can help, and as I have been observing these planets since the 1970s I make a few comments.
The colours of Uranus and Neptune are similar when examined in the eyepiece. I have always described Uranus as slightly bluish-green, in reflectors of up to 1 metre aperture. That was again my experience several times late in 2023 using a 254 mm reflector. To my eye Neptune is just a little more bluish, but not much more so than Uranus. Of course, without a close conjunction, one cannot compare them in the same field of view!
I wonder if someone can work out when such an opportunity will occur? Doubtless it has already been done!
Dear Richard,
I fear we’ve got a while to wait for such a conjunction. By my calculations, the next will be in 2164-6 (0.8-degree separation). A graph of the angular separation of the pair around this time is here: https://in-the-sky.org/graphs.php?gtype=8&startday=7&startmonth=1&startyear=2162&duration=8&obj1type=1&obj1txt=Uranus&obj2type=0&obj2txt=Neptune
However, my calculations also suggest there was a recent conjunction of the pair (less close; 1 deg separation) in 1993: https://in-the-sky.org/graphs.php?gtype=8&startday=7&startmonth=1&startyear=1992&duration=7&obj1type=1&obj1txt=Uranus&obj2type=0&obj2txt=Neptune . I’m a few years too young to have observed that, but I’m sure there are plenty of others here who would have done!
Cheers,
Dominic
Surely comparing the low dispersion spectrum of Uranus with that of Neptune would seal the discussion pretty well?
We have Uranus spectra in the BAA database but Neptune only in the IR
I remember a comparison of the spectra by Christophe Pellier using a Star Analyser
https://www.cloudynights.com/topic/645833-neptune-full-spectrum-comparison-with-uranus/
(Very similar but Uranus has slight red/green bias compared with Neptune )Cheers
RobinThis might be worth a read: MNRAS 527, 11521–11538 (2024)
18 fun packed pages… https://academic.oup.com/mnras/article/527/4/11521/7511973
Figure 1 is interesting.
Figure 1 is interesting
That pretty much matches what Christophe saw with the Star Analyser. If you normalise the spectra in the red/green then Neptune shows a slight blue excess and both planets have similar depth Methane absorption bands
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