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Odd Stellarium problem


Tommohawk

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I have the HEQ5 hooked up to the lappy with Stellarium 15.0 using Lynx FTDI cable - all works fine except...

I've always noticed that when imaging planets the target seems to drift all the time - it needs constant correction by small amount mostly EW but also a bit NS. I always assumed my PA was a bit off and just lived with it. But tonight I notice for the 2nd time that the scope "target" on Stellarium doesnt stay with the planet - in this case Jupiter. Its drifting all the while and seem to match roughly the actual drift on the live view screen.

I don't understand that at all - any ideas please?? 

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2 thoughts come to mind:

Jupiter being a planet is moving, that is how they got their name. Not sure what the angular velocity difference is compared to sidereal for Jupiter. U/D might be owing to we are not all on the ecliptic.

The other one is that for a spell Jupiter will be moving in retrograde - going the wrong way - so your mount is moving L-R and Jupiter could be going R-L. I guess this occurs for a period after our closest encounter which was April 7th. So now I would half suspect that we are moving "faster" then Jupiter so it appears to be going the wrong way. The rate is not great but it likely could show up as it is a not sidereal to start with and is also moving in effect -ve.

From this chart (not overly easy) it looks as if from Feb 2017 until June 2017 Jupiter is in retrograde (going the "other" way).

http://www.nakedeyeplanets.com/jupiter.htm

 

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Hi Tom

I can't help really.... but are you guiding? I take it your using the C9.25 for Jupiter? You may be drifting for some reason which could be balance, or possibly PA. My experience of the belt drive is that good balance is required - in fact, very good balance, otherwise the scope can drift to one side even if guiding seems very good. You can tell this by where the cluster on the PHD2 bullseye target is. Of course, it should be around the centre but if it's to one side, I'd look at the scope balance.

Louise

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If you are using EQMOD try clicking on one of the TRACKING RATE Icons near the bottom of the control panel ( Stars, Moon, Sun, Comet symbol )

Failing that I would look at PA. Make sure you have good polar alignment.

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7 hours ago, ronin said:

2 thoughts come to mind:

Jupiter being a planet is moving, that is how they got their name. Not sure what the angular velocity difference is compared to sidereal for Jupiter. U/D might be owing to we are not all on the ecliptic.

The other one is that for a spell Jupiter will be moving in retrograde - going the wrong way - so your mount is moving L-R and Jupiter could be going R-L. I guess this occurs for a period after our closest encounter which was April 7th. So now I would half suspect that we are moving "faster" then Jupiter so it appears to be going the wrong way. The rate is not great but it likely could show up as it is a not sidereal to start with and is also moving in effect -ve.

From this chart (not overly easy) it looks as if from Feb 2017 until June 2017 Jupiter is in retrograde (going the "other" way).

http://www.nakedeyeplanets.com/jupiter.htm

 

Hey that's a really good point! Of course Stellarium can always find Jupiter on a go to basis, but tracking will be off if sidereal.

I'll try and track Jupiters position on Stellarium relative to the background stars and see if there's a discrepancy and if so whether it matches.

Also I should be able to replicate this just by hooking up the mount without the scope and see if the same error recurs. I can repeat the operation on a nearby star and presumably no error will show.

I'll try this later - had a late night and early start so not quite awake yet!

 

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18 minutes ago, Tommohawk said:

Hey that's a really good point! Of course Stellarium can always find Jupiter on a go to basis, but tracking will be off if sidereal.

It is not only off sidereal but at this time I believe it is actually going the other direction, so would be be sort of (Sidereal+RV) where RV = Retrograde Velocity. All the planets outside of our orbit display this but the further away the lesser the extent. Mars would be worse, Saturn less. But Jupiter is the only one around at present and from what I could find is actually in its retrograde phase.

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Actually looks like I was wrong about it being less on more distant planets. If you select Saturn from that link then it spends about two thirds the time moving forward and a third going backwards.

Suppose that is us (earth) catching up with Saturn then overtaking it and seeing it move backwards against the rest of the sky.

Maybe more time in "reverse" but less angular shift.

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Just now, ronin said:

It is not only off sidereal but at this time I believe it is actually going the other direction, so would be be sort of (Sidereal+RV) where RV = Retrograde Velocity. All the planets outside of our orbit display this but the further away the lesser the extent. Mars would be worse, Saturn less. But Jupiter is the only one around at present and from what I could find is actually in its retrograde phase.

 

59 minutes ago, ronin said:

Actually looks like I was wrong about it being less on more distant planets. If you select Saturn from that link then it spends about two thirds the time moving forward and a third going backwards.

Suppose that is us (earth) catching up with Saturn then overtaking it and seeing it move backwards against the rest of the sky.

Maybe more time in "reverse" but less angular shift.

Yes, take your point - it could be out in either direction but from what you its its retrograde now. As you say the differences between planets is probably due to their different respective "year" lengths / relative angular speed cf Earth.

Re Stellarium - the plot thickens!

If I go to any star near Jupiter (or any star in fact) on Stellarium and centre it, and then wind the time forward, its position shifts away from the centre. This makes it difficult to judge if Jupiter is moving WRT the stellar background.

Maybe I'm missing something obvious - again! - but why doesn't Stellarium maintain the centre position? Its very obvious when zoomed in. The same problem is evident even if going to sensor or ocular view, and selecting the NCP. The location seems to change. How can this be?

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