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SkySafari "Measure From Selection" in Arc-seconds

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#1 Rustler46

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Posted 04 January 2020 - 12:23 AM

In the past I have found in SkySafari Pro 6 the "Measure From Selection" tool to be quite useful when double star observing. It would supply angular separation and position angle between two stars of interest. I could just select the first star, choose Selection, then Measure From Selection. Clicking on the second star would then give separation in arc-seconds and position angle - quite helpful for identifying components of double or multiple stars.

 

Now something has changed. The same procedure gives separation in light years, not angular separation. So perhaps I've inadvertently changed something in Settings.

 

Does anyone one know what might be amiss? Any help would be greatly appreciated.

 

Best Regards,

Russ



#2 csa/montana

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Posted 04 January 2020 - 12:26 AM

Moved to Astronomy Software & Computers for better fit of topic.



#3 Jon Isaacs

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Posted 04 January 2020 - 12:56 AM

Russ:

 

When I do a measure from, it seems to provide the separation, the position angle as well the distance between the two in appropriate units.

 

I haven't upgraded my phone yet to the latest system but one of my tablets has been.  I will see what it does.

 

Jon


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#4 hcf

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Posted 04 January 2020 - 01:00 AM

This is on SS6 Pro. I just tried ...

For some pairs of stars I see both angular separation and distance (Albireo,Mintaka), and for others I see only angular separation.

 

Which particular stars show you only distance?



#5 Rustler46

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Posted 04 January 2020 - 02:23 AM

This is on SS6 Pro. I just tried ...

For some pairs of stars I see both angular separation and distance (Albireo,Mintaka), and for others I see only angular separation.

 

Which particular stars show you only distance?

I was just looking at BU 449, an interesting multiple star in Cygnus. Between that star and HD 206225 (in the vicinity) I get 701 light-years. 

 

I'll try Albireo. Measuring between Beta-1 and Beta-2 Cygni I get 34.6 LY. So it must be some setting that has been changed. It used to always give angular separation and position angle. Now it gives light-years. I must have changed a setting somewhere.

 

Looking at the Help topic "Measure From Help" it doesn't mention any option other than angular separations. I'll  try restoring defaults. In Settings > User Data > Save & restore Settings > Revert Chart to Factory Defaults - I did this. Still Albireo gives 34.6 light-years separation. 

 

Edit:

This is strange! The separation in arc-seconds is given for A-B in the Info screen as 34.6 arc-seconds. This is suspiciously like the 34.6 light-years given by the measure-from function. Hmmmmm.


Edited by Rustler46, 04 January 2020 - 02:45 AM.


#6 Rustler46

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Posted 04 January 2020 - 03:36 AM

Russ:

 

When I do a measure from, it seems to provide the separation, the position angle as well the distance between the two in appropriate units.

 

I haven't upgraded my phone yet to the latest system but one of my tablets has been.  I will see what it does.

 

Jon

I've tried resetting screen settings to factory defaults. And I still get light-years not arc-seconds. There is something I've done to get it off kilter. I'll keep looking. Interestingly I checked SkySafari on my iPhone-6 and it acts the same. So behavior is linked on both my iPad Mini-1 and iPhone-6.



#7 Jon Isaacs

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Posted 04 January 2020 - 05:36 AM

Russ:

 

I checked my tablet and it also shows angular separation, position angle and linear separation.  

 

I am using the Android version so maybe you can find someone also using the iOS version.  Sometimes issues like this are mistakes that have slipped in during an upgrade and were not caught by the programmers.

 

Jon



#8 Michael2

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Posted 04 January 2020 - 06:48 AM

Russ, I just checked in SkySafari 6 Pro on my iPad and it shows in light years only. Could not find anything in settings that could be changed.

 

Mchael.



#9 The Ardent

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Posted 04 January 2020 - 07:04 AM

Same here. 

 

Russ, I just checked in SkySafari 6 Pro on my iPad and it shows in light years only. Could not find anything in settings that could be changed.

 

Mchael.



#10 Jon Isaacs

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Posted 04 January 2020 - 07:46 AM

This is strange! The separation in arc-seconds is given for A-B in the Info screen as 34.6 arc-seconds. This is suspiciously like the 34.6 light-years given by the measure-from function. Hmmmmm.

 

I noticed that too.  I checked Castor and it gave a reasonable number.  

 

It occurred to me that Albireo could be an optical double and that the distance given is actually the distance between the two components in the Z direction.

 

Looking Albireo up on Wikipedia indicates this could be the case.

 

https://en.wikipedia.org/wiki/Albireo

 

"It is not known whether the two components β Cygni A and B are orbiting around each other in a physical binary system, or if they are merely an optical double. If they are a physical binary, their orbital period is probably at least 100,000 years.[32] Some experts, however, support the optical double argument, based on observations that suggest different proper motions for the components, which implies that they are unrelated.[33] The primary and secondary also have different measured distances from the Hipparcos mission – 434 ± 20 light-years (133 ± 6 pc) for the primary and 401 ± 13 light-years (123 ± 4 pc) for the secondary.[9] More recently the Gaia mission has measured distances of about 330–390 light years (100–120 parsecs) for both components, but noise in the astrometric measurements for the stars means that data from Gaia's second data release is not yet sufficient to determine whether the stars are physically associated.[34]"

 

Apparently, the distance between A and B has not been clearly established.  It is possible that Sky Safari is using the Hipparcos data and is estimating the distance at 34.6 light years.

 

As far as your troubles.  My version of Sky Safari 6 pro measures the distance between A and B as:

 

34.6" @54.3 deg  34.6 ly

 

Jon



#11 ascii

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Posted 04 January 2020 - 08:05 AM

I noticed that too.  I checked Castor and it gave a reasonable number.  

 

It occurred to me that Albireo could be an optical double and that the distance given is actually the distance between the two components in the Z direction.

 

Looking Albireo up on Wikipedia indicates this could be the case.

 

https://en.wikipedia.org/wiki/Albireo

 

"It is not known whether the two components β Cygni A and B are orbiting around each other in a physical binary system, or if they are merely an optical double. If they are a physical binary, their orbital period is probably at least 100,000 years.[32] Some experts, however, support the optical double argument, based on observations that suggest different proper motions for the components, which implies that they are unrelated.[33] The primary and secondary also have different measured distances from the Hipparcos mission – 434 ± 20 light-years (133 ± 6 pc) for the primary and 401 ± 13 light-years (123 ± 4 pc) for the secondary.[9] More recently the Gaia mission has measured distances of about 330–390 light years (100–120 parsecs) for both components, but noise in the astrometric measurements for the stars means that data from Gaia's second data release is not yet sufficient to determine whether the stars are physically associated.[34]"

 

Apparently, the distance between A and B has not been clearly established.  It is possible that Sky Safari is using the Hipparcos data and is estimating the distance at 34.6 light years.

 

As far as your troubles.  My version of Sky Safari 6 pro measures the distance between A and B as:

 

34.6" @54.3 deg  34.6 ly

 

Jon

There is a bug in the iOS version of SkySafari 6 Pro (don't know about the non-pro). It has been reported on their support forum.  I never get the angular separation anymore, just the distance in light-years. For Albireo, all I get is the 34.6 ly measurement.  I expect that there will be an update to fix this.


Edited by ascii, 04 January 2020 - 08:07 AM.

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#12 Jon Isaacs

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Posted 04 January 2020 - 08:25 AM

There is a bug in the iOS version of SkySafari 6 Pro (don't know about the non-pro). It has been reported on their support forum.  I never get the angular separation anymore, just the distance in light-years. For Albireo, all I get is the 34.6 ly measurement.  I expect that there will be an update to fix this.

 

As I had said in my first post, I am using Android so it all makes sense... 

 

Bill and Tim were iOS guys so over on this side, we tended to suffer a bit, not unexpected.  When they decided to port Sky Safari to Android, that was just super and I expected we would suffer a bit, I was just grateful that they had decided to make the effort to do the port. 

 

Tim did say at one point that he finally felt that the Android version was the equal of the IOS version, that might have been Android version 5.. 

 

Whatever the issue, I'm sure they'll get it fixed. 

Or maybe in the interest of equality, they'll just put the same bug in the next Android update.. :lol:

 

Jon  



#13 Carbstone

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Posted 04 January 2020 - 08:38 AM

Russ,

 

On my MacBook Air (MacOS Catalina 10.15.4 & SkySafari 6 Pro 6.4.0): separation & position angle.

On my iPad Air (Software version 12.4.4 & SkySafari 6 Version 6.6.1): since the update of 27 Dec 2019 light years only!  

 

In both versions it is not possible I to change the settings.

 

Regards,

Dirk


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#14 ordep

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Posted 05 January 2020 - 12:41 PM

Thank you for the report.  The Dev team will take a look at this.  Pedro


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#15 Rustler46

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Posted 05 January 2020 - 06:00 PM

Thank you for the report.  The Dev team will take a look at this.  Pedro

Nice to see you are looking into this problem - great customer service! If possible an option to choose arc-sec/angle or L.Y. would be nice. If not possible, then the angular measurement is most useful. Thanks!

 

Best Regards,

Rustoleum


Edited by Rustler46, 06 January 2020 - 02:00 PM.

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#16 Michael2

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Posted 13 January 2020 - 05:09 AM

I think they have fixed it!

 

Michael.


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#17 ascii

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Posted 13 January 2020 - 07:13 AM

I think they have fixed it!

 

Michael.

 

I'm running SkySafari 6.6.3 released yesterday for iOS.  The release notes say that the angular separation feature has been fixed.  I checked a handful of measurements and the angular separation readout worked fine for all of them.


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#18 alphatripleplus

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Posted 13 January 2020 - 08:54 AM

Sounds like good news!




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