Interesting with the shortwave IR is that we can see the bright daylit side by reflected sunlight, and some emitted light on the nightside (right).

I aspire, later this year, to become part of the small group of amateurs to make this observation from Earth. Christophe Pellier first did this in 2004; it's the glare from the dayside that makes this challenging. From Earth, there is the additional challenge that such an observation entails that the Sun is close to Venus in any such situation, making the day sky an additional source of noise (though minimized in IR, if sky conditions are good). That's no issue for Akatsuki.

It's an interesting issue for IR imagery at ~1-5 microns of Venus and, for that matter, Io, that reflectance/absorption and emission all play a part.

For Io's volcanoes, the thermal signal is much stronger at shorter wavelengths, but the reflectance signal is still stronger yet, so effective thermal imagery of Io (the dayside, which is all we see from Earth) has to be done at longer IR where the signal is weaker but the competition with reflectance is weaker still.

With Venus' nightside, reflectance does not occur except in that the sunlit crescent can offer noise. At somewhat longer (≥2 microns) wavelengths, the clouds block the radiation coming up from the surface, so we end up measuring cloud thickness as backlit by the surface glow, and ~1 micron, we see the surface itself.

As far as I know, there's no groundbreaking science to be done in imaging the surface at regional-scale resolution, but it certainly is a neat accomplishment to do so from Earth. The clouds, meanwhile, offer a lot of science opportunities. However, I don't know of any amateurs with gear for 2 micron imaging.

Some new pictures I made today

Superb, Ant! Some of the best Venus images that exist. It really brings out how the equatorial regions look more chaotic on this scale than do the higher latitudes.

I've attempted to make some pseudo-true color views using the 360nm UV and 0.90 μm IR cameras. I realize these are poor approximations of the actual visible spectrum appearance of Venus, but those are kinda boring anyway!

These are wonderful. A similar palette is being used by many amateurs making IR/UV images at much lower resolution.

A couple of attempts to merge the sunlit cloud deck imaged in near-UV and near-IR with nighttime thermal data taken at the 2.26 micron wavelength, which appear to be the least overexposed of the 2 micron camera images. The two sets of images were taken up to 2 hours apart, so the geolocation of these images probably isn't super accurate but should be fairly representative. I've also added a heat colormap to colorize the thermal infrared data - the scale doesn't correspond to specific temperatures or anything, it's just there to enhance some of the detail present in those images while also emphasizing that it's thermal data.

Nice display of IR! It certainly gives the impression that we should not touch Venus without protective gloves.

It's hard to tell from just a couple of images, but I'd like to see a global average of limb darkening. There should be some limb darkening but in any single image, the regional variations are a bigger factor.

I would guess the limb darkening has an interesting dependence on phase angle and location along the limb. A fun simulation project as well.

I'm curious whether any of the recent data or images would show how much limb darkening Venus exhibits at a low phase angle (fully lit). Is it possible to assess this with an image using only visible wavelengths?

That's an issue that I would love to see addressed. It certainly seems in all images that I've seen that this has at least some difference, though subtle, across the visible spectrum.

Venus Express imaged a glory on Venus, which implies that such a thing is perhaps in their data, unless the whole disk was not imaged. I haven't seen any such image that captures such a wide view.

Over the last few months I've been extremely eager to get a terrestrial photo of Venus at its fullest. I captured an image just four days ago with Venus at a phase angle of 18.5°. (And immediately thereafter, an image of Mercury.) I wish it'd been less, and/or that the quality were higher, but weather has not been helping me out. I've seen few terrestrial images of a relatively "full" Venus in color. Perhaps what you are looking for can be approximated with this or a better terrestrial image.

Click to view attachment

How nice ! Thanks very much jccwrt (and also to Ant103) : I'm feeling the heat too

Indeed now's a good time to get low phase angle images from Earth as JRehling did 2 posts up. I found this reasonably low phase angle view from MESSENGER (sorry this isn't Akatsuki) posted at The Planetary Society and processed by ugordan. Looks like there's some darkening even on the brighter limb. Interesting to see also how the subtle details look with the visually realistic processing.

http://www.planetary.org/multimedia/space-...01387b94_o.html

I have been thinking, ever since, and I may be going mad...?

If Akatsuki managed to enter whatever orbit it is in now with only chemical thrusters, then all future missions may benefit from not having
a large main engine. Instead, they can carry more instruments?

It will also be cheaper to make?

P

The main engine was most efficient, it was expressly designed to be good at Venus orbit insertion; the minor thrusters used much of the fuel and had to burn for much longer, to barely get into a much larger, less scientifically optimal orbit around the planet.
Ion thrusters so far have worked well for reaching small bodies (like Hayabusa 2, Dawn, etc.) New generations of ion engines might make them more usable at planets (see the Bepicolombo mission for an example).

Compare the apoapses of various Venus orbiters:

Venera 15: 72,078 km
Pioneer Venus: 66,630 km
Venus Express: 63,000 km
Magellan: 7,762 km
Akatsuki (planned): 80,000 km
Akatsuki (actual): 330,000 km

All had relatively low periapses, so the Magellan orbit was somewhat circular, but the others were all highly elliptical, with Akatsuki's orbit being by far the most elliptical.

The greater the apoapsis distance, the more time that the orbiter spends far away from the planet, reducing resolution of imagery. That is why a closer orbit is more desirable. (Although an orbit that is too close would be unable to image large portions of the planet at a time.) The energy requirements for getting into a low-apoapsis orbit are much greater than for a high-apoapsis orbit.

For this reason, it is expensive to get into a low-apoapsis orbit, but it is still desirable, to increase the science return. Measuring the value of science, though, depends upon the goals. Akatsuki can still perform great observations, but it gets fewer of them in a given amount of time at high resolution because of the engine failure. Maybe for some science goals this is not that important, but generally, mission planners have valued the higher rate of return of the most detailed imagery.

Venus, Earth and the Moon:
https://i.imgur.com/xiF7aZx.png

Source:
http://darts.isas.jaxa.jp/pub/pds3/staging...174_l2b_v10.fit
http://akatsuki.isas.jaxa.jp/en/topics/news/001085.html

Some new pictures I made yesterday from a new batch of RAW imagery.



http://www.db-prods.net/blog/2018/10/28/no...s-par-akatsuki/

Anorther remarkable view of the Venusian atmosphere Damia!
The level of detail is impressive here.
Can you imagine a Zeppelin in the highly dynamic upper atmosphere of Venus?

courtesy of this forum's Ralph Lorenz

Listen to the radio wave passing through Venus' atmosphere

Following the inspiring work of Damia on the basis of Akatsuki data, I've recently represented Venus and the Earth at scale.
Here is the outcome:

I love the comparison. Every now and then I'll look at some hills (on Earth) and imagine how there's some Venusian equivalent up there, of comparable size but different in so many details. Your picture captures the mystery those clouds hid for so many centuries.

Our sister planet!
It could have been a tropical world with mean temperatures comparable to the temperatures they are encountering in Australia at the present time but that's far from being the case!
Even at the top of Maxwell Montes, it is a hell!

some nice animation of the Venusian clouds from this most neglected mission:

Venus puts on variety show among its cloud-tops

Those animations are magnificent and suddenly make understandable the dynamics that cause the famous Y shape.

This is a great mission.

UV Venus animation from this dataset: https://atmos.nmsu.edu/PDS/data/vcouvi_1002/data/l2b/r0100/

some important new result from Akatsuki (the article, unfortunately is paywalled)

How waves and turbulence maintain the super-rotation of Venus’ atmosphere

This de-rotated animation shows the night side of Venus in IR.
Near the center you can see a giant, previously unknown planet-scale wave feature.
The animation covers about 14 hours of observations

Beautiful work, Roman. I have photographed Venus in UV regularly and it's nice to see the cloud motion occur on this time scale. From Earth, one can see about 3 hours maximum in sequence, and then the change a day later, after which the planet has rotated 90°. Many of the details here are moving on a scale of minutes and it both beautiful and illuminating.

I'm unsure what the planet-scale wave feature is: Is that dark curve across the middle the feature, or an artifact?

Akatsuki found a gigantic planet-scale wave running north to south early in its mission, but the imagery didn't look much like this. Is this another example of that phenomenon?

Lightning caught on Venus finally?

https://www.nationalgeographic.com/science/...ngonvenus::rid=

P

An animation of Venus I produced on the basis of ultraviolet data acquired from the Akatsuki probe on October 30, 2021.
25 images mobilized to generate an animation via extrapolations...
Time scale: 5 seconds in the sequence = 1 hour real time.

https://www.youtube.com/watch?v=btJ7AmXGWOw

Current amateur UV studies of Venus are amazing.

One correction: the rotation period of Venus is 243 days and the superrotation of the atmosphere is 96 hours, so that "day later" was a view of the atmosphere.

Lovely animation.
Has that N-S wave been corellated with a topo feature?

I have seen several papers associate this feature or others like it with Aphrodite Terra. Here is an example:

https://www.nature.com/articles/ngeo2873

(Large stationary gravity wave in the atmosphere of Venus, by Fukuhara et al., 2017.)

Phil

A caveat there – the cloud rotation may average about 96 hours but that varies quite a bit, so in any particular span of 3 to 5 days, you might get just about exactly one rotation of the clouds, but you might also have quite a bit of error. Venus Express had some results characterizing this variation, which I think remains unpredictable.

Yes, the upcoming explorations of Venus will be quite exciting. Not only modern radar imaging of the surface, but also detailed IR imaging. And by itself Venus has one of the more fascinating atmospheres. Robotic probes floating in the "habitable zone" of the atmosphere could be a reality.

--Bill

JAXA announced that they lost contact with the Akatsuki orbiter in late April, and have been unable to re-establish communications (though they will continue to try)
With the end of the Akatsuki mission, there are no longer any operating spacecraft orbiting Venus.