Best App for depicting position of Jupiter's GRS?

[JeremyS]

I was observing Jupiter last evening and was enjoying a transit of the GRS. However, I notice its position on Sky & Telescope's "Jupiter's Moons" App was incorrect.  It was out by about 45 mins (estimate). I notice that several online sources, including S&T each give a different time, sometimes markedly different. I assume this is because the longitude of the GRS drifts with time and some Apps/programs don't update with the correct longitude.

Has anyone come across a decent iPhone App that accurately displays Jupiter with the GRS?

I have Sky Safari Pro, which lists transits times. Is there a way of getting it to display a real time image of Jupiter with the GRS?

[johninderby]

I use the iPad version of Luminos which I found to be the best of any I’ve tried. Settings allows you to set it up to your lo your local observing location. I compared Sky Safai Pro and Luminos and deleted Sky Safari after comparing it to Luminos.

Think the iPhone version is a bit different but here’s a couple of screen grabs from the iPad version. 

Edited August 19, 2020 by johninderby

[Captain Scarlet]

I wonder if it's a coincidence that "light time" from Jupiter is around 45 minutes

[Stu]

28 minutes ago, JeremyS said:

I have Sky Safari Pro, which lists transits times. Is there a way of getting it to display a real time image of Jupiter with the GRS?

Just zoom into the image of Jupiter and GRS position is displayed correctly Jeremy. EDIT when I say correctly....... that may not be the case. It differs from the JupiterMoons app and I guess depends on when the meridian point was updated in the app. It has always seemed fairly reliable to me, but the other day I noticed it was a bit off when observing GRS. Treat with caution I guess.

Also, if you go to the information page, you can tap on the clock symbol on the right hand side of each event and it automatically takes you to that time.

@Captain Magenta light time seems to be 36 mins currently. I recall one of the apps, possibly JupiterMoons or was it Stellarium, there was a tick box to say allow for light travel time which then showed it correctly as seen on earth.

[markse68]

9 minutes ago, Stu said:

@Captain Magenta light time seems to be 36 mins currently. I recall one of the apps, possibly JupiterMoons or was it Stellarium, there was a tick box to say allow for light travel time which then showed it correctly as seen on earth

SS seems to have it too

 

[JeremyS]

Many thanks @Stu: indeed zooming in works - thanks 🙂 .

Now I'm left with the issue that Sky Safari  predicts a GRS transit today at 17.46. This is the same time as predicted by the S&T App, which is wrong.  Note that I have "Light Time" setting as On (green")

Luminos as suggested by @johninderby predicts 18.26, i.e. 40 mins later. This sounds as if it might be correct given  my experience last night.

S&T website predicts 18.16

I suspect the differences are due to using the incorrect (i.e. not updated longitude of the GRS. Has anyone found a way of doing this?

 

Edited August 19, 2020 by JeremyS

[JeremyS]

10 minutes ago, markse68 said:

SS seems to have it too

Thanks Mark. However, I find the same predicted GRS time whether "Light Time" is On or Off in Sky Safari

[johninderby]

I have found Lumnos seems to be accurate. The 18:26 transit is below the horizon though.

[Geoff Barnes]

I've always found this website useful and accurate for Jupiter...https://shallowsky.com/jupiter/

[markse68]

6 minutes ago, JeremyS said:

Thanks Mark. However, I find the same predicted GRS time whether "Light Time" is On or Off in Sky Safari

It still happens at the same “time” but the display does change- on mine anyway. First pic is with it on, second with it off for same time

[JeremyS]

11 minutes ago, markse68 said:

It still happens at the same “time” but the display does change- on mine anyway. First pic is with it on, second with it off for same time

So it does, Mark! Turning Light time off makes it appear that the GRS has rotated further across the disc. So I need light time "on", which is how I have used it. But I'm pretty sure it still shows the GRS has rotated further than what reality tells me it has 🤔

It's also curious (and not helpful) that it doesn't change the predicted transit time in the events list 

Edited August 19, 2020 by JeremyS

[markse68]

3 minutes ago, JeremyS said:

So it does, Mark! Turning Light time off makes it appear that the GRS has rotated further across the disc. So I need light time "on", which is how I have used it. But I'm pretty sure it still shows the GRS has rotated further than what reality tells me it has 🤔

It's also curious (and not helpful) that it doesn't change the predicted transit time in the events list 

I’ll have to check again next time we get a clear patch but I’ve always found it pretty accurate esp with moon transits

Mark

[JeremyS]

16 minutes ago, Geoff Barnes said:

I've always found this website useful and accurate for Jupiter...https://shallowsky.com/jupiter/

Many thanks Geoff. The webpage doesn't list GRS transits in the events lists (only moons). The animation shows the moons moving, but only indicates the GRS as a "GPS" text below the pic of the planet. Does the App version show the actual planetary disc with the GRS location in real time? And do you know if the predicted position is correct?

[JeremyS]

1 minute ago, markse68 said:

I’ll have to check again next time we get a clear patch but I’ve always found it pretty accurate esp with moon transits

Mark

Thanks Mark. As far as I can see the S&T App is spot on regarding moons and shadows etc, too. It's just the GRS that's a problem. Which makes me think some of these programs don't use its correct longitude.

[Geoff Barnes]

Yes @JeremyS I've just noticed the GRS is missing on the image, it always used to be there. I haven't used the app since last year because Jupiter hasn't been in view but it was there last time I used it and was always pretty accurate. I shall investigate!  

[Geoff Barnes]

I've just sent an email to the website designer enquiring about the missing GRS, will report any result as and when...

[markse68]

18 minutes ago, JeremyS said:

Thanks Mark. As far as I can see the S&T App is spot on regarding moons and shadows etc, too. It's just the GRS that's a problem. Which makes me think some of these programs don't use its correct longitude.

Interesting observation Jeremy. Here’s a thought- what with it being a huge vortex storm in a really huge ball of gas could it be moving about a bit of its own accord? Like our own weather does? It’s never going to be as predictable as a crater or mountain on a rocky planet? The image/model they’ve used in SS looks like it could be quite out of date as GRS looks smaller now through my scope, and redder/orangier

Edited August 19, 2020 by markse68

[JeremyS]

Just now, markse68 said:

Interesting observation Jeremy. Here’s a thought- what with it being a huge vortex storm in a really huge ball of gas could it be moving about a bit of its own accord? Like our own weather does? It’s never going to be as predictable as a crater or mountain in a rocky planet.

Yes it certainly does move around, Mark - and quite a bit. Hence the longitude needs to be updated regularly. I really wonder how many Apps actually do this.

I now see the SS GRS issue has been discussed on CN too. One person suggested updating the following:

"Try this:    Settings/solar system/update minor body orbit data. It's at the bottom of the page. I update this setting frequently. Not sure if the rotation updates but that's where I would assume it to be."

I just did that update (takes a while), but the predictions of transits are the same as before, so i doubt if the GRS longitude was updated.

[markse68]

Does Jupiter count as a minor body? 😳

edit- didn’t make a difference to displayed position on my phone either

PS I thought you were talking about our longitude- doh 🤦‍♂️😂

Edited August 19, 2020 by markse68

[Guest]

I've got an app on my laptop called Jupiter 2, I think it's written by someone from France.

http://www.astrosurf.com/rondi/

Edited August 19, 2020 by Guest

[JeremyS]

11 minutes ago, markse68 said:

PS I thought you were talking about our longitude- doh 🤦‍♂️😂

This plot shows how significant the longitudinal drift of GRS is.

[markse68]

11 minutes ago, JeremyS said:

This plot shows how significant the longitudinal drift of GRS is.

Help me understand what i’m looking at there Jeremy- is it the wobbles in the plot or the overall slope? If the latter, what are they using as a datum to measure drift from?

[JeremyS]

23 minutes ago, markse68 said:

Help me understand what i’m looking at there Jeremy- is it the wobbles in the plot or the overall slope? If the latter, what are they using as a datum to measure drift from?

The slope shows the drift relative to system 2 Jovian longitude (shown on the X-axis at the bottom). This is the "datum".

The plot suggests that from Feb to Aug this year, the GRS will drift 16 degs in longitude from the average system 2., or about 4.4% of a full rotation. System 2 rotation is about 9 h 55 mins, so the drift equates to 26 minutes between Feb and Aug. Quite alot! Hence any software should allow for this.

From Project Pluto software:

The second complication is that Jupiter has three different systems of longitude. This problem arises because Jupiter doesn't rotate as a solid object; clouds near the equator rotate a little faster than those closer to the poles. So System I is used for measuring features close to the equator, and System II for features in the temperate regions. And when radio bursts were detected on Jupiter, it was found that they rotate at yet a third rate, so a System III had to be created. This is the rate of rotation of the core of Jupiter, and is of essentially no interest to visual observers. The GRS is far enough from the equator to be measured in System II.

[JeremyS]

So a bit more digging. I think the S&T online calculator shows the most correct GRS transit time. They claim to update the GRS longitudinal drift and last did so in June:

"These predictions assume the Red Spot was at Jovian System II longitude 333° in June 2020 and continues to drift 1.75° per month, based on historical trends noted by JUPOS. If the GRS moves elsewhere, it will transit 12⁄3 minutes late for every 1° of longitude greater than that used in this tool or 12⁄3 minutes early for every 1° less than the longitude in this tool."

Annoying the App (that they link to from that page), doesn't seems to have been updated with the correct longitude of the GRS. And neither, I assume, has Sky safari, since it shows the same transit time as the S&T App. Its a good 30 minutes out, which is easily visible in the telescope. 

Edited August 19, 2020 by JeremyS

[Geoff Barnes]

Hi @JeremyS, here is the reply to my enquiry regarding the missing GRS...

You're right! Apparently the way clipPath works in browsers has
changed (not too surprising, it was never really documented and I
was always guessing at how to make it work) and that's making the
GRS invisible. I'm working on it; hopefully will have something
working by tomorrow.

Thanks for the report. I'll let you know when it's fixed.

Sounds hopeful!