73 replies to this topic

[rehling]

That's a superb answer Darin. I've noticed, though, that some of the better images of Venus in UV used larger SCTs. In particular, Damian Peach has posted some great ones taken in 2007 with a C9.25. I suppose the upshot here is that they are good but could have been better with a similar aperture Newtonian?

 

Here's a great result with a larger Newtonian:

 

http://www.astropix....in-ultraviolet/

 

And Phil Miles did some great work with a huge mirror and without the pesky SCT corrector:

 

https://www.cloudyni...c/553932-venus/

 

Still, I'm thinking that the C9.25 might be my next telescope… Though that can change by the hour.

[evan9162]

Another session this morning.  Decent seeing. 

 

[evan9162]

Pretty good seeing this morning.  Getting closer to the sun, so the sky is a bit more washed out (harder to locate visually)

 

[rehling]

Now that we're past the solstice, I can get Venus significantly before sunrise, which is a huge relief, just to have the time pressure relieved.

 

This was at 20170708 UTC 1245. As a small bit of post processing, I subtracted a Lambertian sphere with the matching phase angle from my image, which made the contrast more consistent as a function of longitude… only noticeable near the limb and near the terminator.

 

The current phase gives me useful data covering about 75° of longitude. The mean cloudtop rotation per day is 81°, so there's still a wait until about July 21 before the gibbous Venus is wide enough that two consecutive days (with very good seeing) could show an overlap of features. Hopefully, the weather on Earth (clear, good seeing) and Venus (for the winds not to speed up, as they can) will deliver.

 

Darin, this looks like it aligns quite well – surprisingly well – with your (clearer!) photo taken four days earlier, probably shifted a bit east, so the rotation is a bit less than 90° per day. But it's nice to see the patterns in a consistent way after one rotation. We're just about ready to do some serious meteorology.

 

Edited by rehling, 08 July 2017 - 12:35 PM.

[evan9162]

Seeing just mediocre this morning.  There was also a thin haze in the air.  Venus is starting to get difficult to locate visually, as the sky is quite washed out in its vicinity in the morning.  This may be one of my last Venus images this year.

 

[rehling]

I've gotten into a pretty good routine of imaging Venus right before sunrise, and, weather permitting, I should be able to continue for about another month. After that, I'll have to choose between low-altitude before sunrise or better altitude after sunrise. I rarely get more than two good days in a row, with seeing and/or fog obliterating the others.

 

The following images were all taken around 1245 UTC on the following dates:

July 12, 15, 16, 19, 20.

 

 

[evan9162]

Got another unexpected chance this morning. Seeing wasn't too good...

 

[rehling]

Darin, I'm extremely glad you got that, because I also got a pic, though my seeing was excellent, and it looked so symmetrical, I was suspicious about the veracity. We definitely saw the same thing. This was 20170722, 1245 UTC, about two hours before your picture.

 

 

And here was the day before, 20170721. Not as good seeing, but when I divide the UV by an IR image (which is featureless), I get greatly improved detail; this is the raw UV, and I'll post the UV/IR later.

 

 

I now have Venus four days in a row, and therefore theoretically a complete 360° view. It seems like the patterns may have changed substantially, though, and don't match what was up four days ago.

 

The forecast indicates I should likely be able to continue the streak. I'll make a map projection from my pictures and see how it comes out.

Edited by rehling, 22 July 2017 - 03:49 PM.

[R_Huntzberry]

Hi All,

 

Here's my humble submission, no UV filter (man, those things are expensive!) just a one shot color image using a ASI224MC, TeleVue 2.5x, ZWO ADC and a APM 152ED on the morning of July 22nd.

(My 1st Venus image)

 

 

-Richard

 

[evan9162]

Managed to get in another shot this morning.  Seeing was quite poor.

 

[rehling]

My streak ends at five days because it was too drizzly last night to leave my gear outside and I didn't get up at 4am to let it cool off. Here's my picture from 20170723. Seeing not good; failed to resolve the northern band seen in Darin's picture.

 

[rehling]

On two consecutive mornings, I had very scant breaks between fog. On the 27th, I had just enough time to set everything up and not get a picture. On the 28th, I had just enough time to get the picture.

 

 

It seems like the marine layer fog is good for seeing when you get breaks in it. Through the eyepiece, Venus seemed very still both days. Of course, when there are no breaks in the fog, the seeing is a moot point.

 

I also need to reconsider my frame selection / wavelet options that I'd come to settle upon through experiments using Jupiter and nights of good seeing. This Venus case may be worth trying very different parameters; today, I found that my usual parameters were distinctly worse than another value. Namely, Lynkeos gives an option of rejecting values outside of some z-score (standard deviations) from the mean. I was using 0.1 as a tough threshold, but today I tried 1.0 and it worked strikingly better. I need to revisit the old data I've archived.

 

 

[stanislas-jean]

Hi,
Did you get a picture on 30th?
The 2 bright streaks near the dark band on equator is a matter of a follow-up.
Stanisls-Jean

[rehling]

I've been shut out the last three days due to fog. Stanislas, is there a link to discussion of these white streaks? If the forecast is accurate, I may be able to get regular observations again the first week of August, and the opportunities when weather is good will continue for me at least until late August.

 

By chance, I notice that I have gotten pictures of Venus almost every fourth day of July, so I have a pretty good sequence that is, in theory, showing the same portions of Venus. But, important caveats: On days of bad seeing, the features appear washed out in my pictures, and the period of Venus' cloud rotation is not constant, although it seems to be pretty close to 4 days lately.

[stanislas-jean]

Thanks for you reply.

Some 22nd pictures allow us to have a look on Venus having the presence of 2 bright streaks near the dark equatorial band.

At the BAA we are thinking of some specific occurences merging into the atmosphere, but not surely gravity wave.

The british Body emitted an alert for performing a follow-up on the period commencing 22nd july.

I enclose here a link were it can be found some data results.

http://alpo-j.asahik...atest/Venus.htm

There is surely more results performed by outside observers, this is the case with your issues.

Your data are welcome and your 22nd picture had been sent to our Venus section being on a more conspiscious resolution power.

I am observing too visually with only 90 and 102mm.

One comment: the equatorial speed rotation  is commonly recognised to be 4 days. Just a mark.

In fact between 22nd and 30th data, the morphology pattern had considerably changed were the dark equatorial band is disappeared almost, the 2 bright streaks too. This means simply disappearation or banding dilution.

Data with more or less one day to be collected from the key date would be a must.

Hope this can be performed with the weather we have, here cloudy.

Good skies

Stanislas-Jean

[rehling]

Thanks for the reply, Stanislas-Jean. Very interesting.

 

A very timely break in fog opened things up for a picture this morning. Seeing above average.

 

20170801 1303 UTC

 

[stanislas-jean]

Thanks a lot.
Stanislas-Jean

[rehling]

After a long delay… In San Francisco, we have had an unusually persistent morning fog, which normally comes and goes throughout the summer, but has been relentless throughout August. Mid-day has often been clear, so today, I took pictures of Venus in UV and IR near noon. Tube currents in my hot telescope made the UV image almost featureless, but here is the IR image – also featureless, but you can see the phase quite nicely.

 

For UV images showing detail, I await the next clear morning, if we have one.

 

 

[rehling]

And here is an animation of Venus changing phases over a span of 11 months. I hope I can get several images to bridge the gap as it goes around the back side of the Sun and make this as close as possible to a complete orbit.

 

[rehling]

Cursed with morning fog for 24 days now, I tried to image Venus in the afternoon, and once again found that UV imaging with the sun warming up my telescope is a serious challenge. If I subtract a blue image from the UV image, I get a bit of detail, but at much less resolution than the Venus images taken at/before sunrise that I was taking last month.

 

My tactic was to align the telescope on the Sun, get Venus centered, then throw white towels over my telescope for >30 minutes, and come back to image as fast as I could. My hopes were that the telescope would be near thermal equilibrium as a result, and I have evidence that it helped at least a little, but not as much as I need.

 

I'll post my result as a matter of documenting the approach, with no pride in the quality of the result.

 

[rehling]

Finally, a clear morning, and Venus' geometry in the morning sky is still very favorable for me. Because the seeing was very good, I decided to follow Darin's lead and use my 2x Barlow, which increased my exposures from 6ms to 45ms. A new problem, however, was that the new version of oacapture that I installed did something to my frame rate, so I ended up with about 6000 frames instead of the 30K or so that I'd prefer. That may have cost me a little detail in the clouds, but it still likely matched or exceeded the resolution that I was getting without the Barlow.

 

 

After the streak of 24 days of morning fog, I hope I get a fraction of that number of clear mornings in a row now and take advantage of the rest of Venus' time in my morning sky.

[rehling]

The prodigal (good skies) has returned… Venus clear and bright in good seeing this morning. Again, using my Barlow. Here's the UV. Hopefully there'll be more chances in the week ahead.

 

[Stargazer3236]

Can you include info on your scope, mount and camera please?

[rehling]

Yes, sorry, David… I posted that earlier, but I keep posting new images without context.

 

I have a NexStar 6se, using a 2x Barlow, the Astrodon UVenus filter, and an ASI1600mm.

 

Until/before specified, I was not using the Barlow. Without the Barlow, I was using parameters, typically, of 6ms and a gain of 420 to 480. With the Barlow, I am using similar gain but an exposure of 45ms. My sense is that with better seeing, I'm best off using the Barlow and grabbing fewer frames, but with worse seeing, I need to grab more frames, which necessitates the faster frame rate and foregoing the Barlow. The factor of 7.5 difference in speed is owed to the change in focal ratio (worth ~4x) and how much UV is blocked by the glass (~2x).

 

All of the parameters vary depending upon conditions.

 

I have been trying to image right before sunrise, when the sunlight heats up the scope and creates tube currents, but the changing seasonal geometry is putting the sunrise behind a neighbor's garden, which is giving me flexibility there. Sometimes clouds block the sunrise, and on one occasion, I shot at about 11am, whipping a white towel off the telescope just in time to image, before the scope could heat up.

 

One of my overarching findings is that uncontrollable changes in weather and seasons (and my daily schedule) are preventing me from adopting a consistent methodology. The conditions have been favorable from about June 13 through now in mid-September, so I might say that Venus UV imaging is favorable for about six months per 19-month synodic period… a pretty good percentage of the time compared to Mars. I may say that Venus is the most rewarding object in the sky for me, and I may decide my next telescope based in large part on how it would perform on Venus.