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Local Mean Siderail Time for Toronto w Polarscope

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#1 DuiA1

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Posted 16 April 2013 - 05:56 PM

Anyone kmow why the Local mean side rail time is different between ioptron app and the Scope Help app? It's off by almost 22 minutes. Wondering if this could be the error I'm experiencing with my vixen polarscope. What time should I use to set up my vixen polarscope? UTC, LMT or ET? Thanks in advance.
I'm using this with my new Polarie.

#2 DaveJ

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Posted 17 April 2013 - 06:29 AM

Anyone kmow why the Local mean side rail time is different between ioptron app and the Scope Help app? It's off by almost 22 minutes. Wondering if this could be the error I'm experiencing with my vixen polarscope. What time should I use to set up my vixen polarscope? UTC, LMT or ET? Thanks in advance.
I'm using this with my new Polarie.


Local sidereal time changes by about four minutes per day (actually, closer to 3 minutes, 56 seconds) compared to your local clock. Are you sure you were comparing on the same date and time? Here's what I mean with examples of both from my location: [color="white"]
[/color]
Date         Local clock    LST (Local Sidereal Time)
4/14/2013    21:00:00       09:07:43
4/15/2013    21:00:00       09:11:39
4/16/2013    21:00:00       09:15:36
4/17/2013    21:00:00       09:19:32
4/18/2013    21:00:00       09:23:29

It's the LST (Local Sidereal Time) that you want to use for the offset of Polaris from the NCP.

Edit: I should have added that the LST (Local Sidereal Time) offset calculation depends entirely on your longitude. Are you sure that both programs you're comparing have your correct longitude entered?

#3 DuiA1

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Posted 17 April 2013 - 07:34 AM

I believe I am as the longitude is from the GPS of my ipad. According to the Vixen manual I should be using an offset of 5 degrees but the location of Polaris on the Vixen reticle does not match the orientation on the ioptron app. It matches only if I use a 21 degree offset. Is 21 degrees the right offset for Toronto? Thanks in advance for your help.

#4 DaveJ

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Posted 17 April 2013 - 10:24 AM

I believe I am as the longitude is from the GPS of my ipad. According to the Vixen manual I should be using an offset of 5 degrees but the location of Polaris on the Vixen reticle does not match the orientation on the ioptron app. It matches only if I use a 21 degree offset. Is 21 degrees the right offset for Toronto? Thanks in advance for your help.


?? What offset are they talking about? I'm not familiar with the contents of the Vixen manual nor the iOptron app. Offset 5° of what from what?
I'm not intentionally being dense here, just totally confused as to what you're telling me. :question:

#5 DuiA1

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Posted 17 April 2013 - 04:05 PM

The offset is described in the manual as such: Meridian offset scale (Adjustable between E20 and W20 at 5-degree increments)
This is directly from the manual...
Check the difference between the standard time meridian of
your region and your observing site before you set up the Polarie.
If the observing site is east of standard time meridian, rotate the time meridian indicator in the direction as indicated E on the meridian offset scale.
3
If the observing site is west of standard time meridian, rotate the time meridian indicator in the direction as indicated W on the meridian offset scale.
Hope this helps....

#6 DaveJ

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Posted 17 April 2013 - 04:57 PM

Hope this helps....


Actually, I'm more confused now than before! Would you have a link to the manual, by chance? If I could see the manual along with the diagrams/illustrations of the mount itself, perhaps I'd be able to assist.

#7 DuiA1

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Posted 17 April 2013 - 05:24 PM

Dave, here is the link and thank you for your help. http://www.vixenopti...ARIE Manual.pdf
Sorry for the confusion. Page 24 summarizes this procedure but I just cannot get the reticle in the polar scope to match the orientation shown on the ioptron app on the ipad.

#8 DaveJ

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Posted 17 April 2013 - 05:31 PM

Dave, here is the link and thank you for your help. http://www.vixenopti...ARIE Manual.pdf
Sorry for the confusion. Page 24 summarizes this procedure but I just cannot get the reticle in the polar scope to match the orientation shown on the ioptron app on the ipad.


OK - one more question... is this the iOptron app you're talking about? If so, I'll install it on my wife's iPad when she gets home tonight and see if I can figure out what's going on.

#9 DuiA1

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Posted 17 April 2013 - 05:40 PM

Yes. Its very useful. The view is inverted. The other app I also use is Scope Help which is free. They both give the same result for orientation of Polaris. Unfortunately, I'm trying to replicate the reticle on the Polarie polarscope and I'm failing...operator error I'm sure. Thanks again for your help.

#10 DaveJ

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Posted 17 April 2013 - 06:15 PM

Yes. Its very useful. The view is inverted. The other app I also use is Scope Help which is free. They both give the same result for orientation of Polaris. Unfortunately, I'm trying to replicate the reticle on the Polarie polarscope and I'm failing...operator error I'm sure. Thanks again for your help.


Hi DuiA1, look for a PM which I'll send immediately after posting this reply...

#11 Cotts

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Posted 17 April 2013 - 06:59 PM

The offset is described in the manual as such: Meridian offset scale (Adjustable between E20 and W20 at 5-degree increments)
This is directly from the manual...
Check the difference between the standard time meridian of
your region and your observing site before you set up the Polarie.
If the observing site is east of standard time meridian, rotate the time meridian indicator in the direction as indicated E on the meridian offset scale.
3
If the observing site is west of standard time meridian, rotate the time meridian indicator in the direction as indicated W on the meridian offset scale.
Hope this helps....



The above adjusts for your distance from the 75th meridian in longitude. Toronto's longitude is very nearly 80 degrees so the difference is 5 degrees to the west. So now, when you tell the mount it is 2100 EST the mount will know the exact 'time'.

I'm not sure, however, where sidereal time comes into it. That is, you should not have to enter it ant any time. Your mount's software should take care of that automatically if you have input your time zone, your Daylight saving info, the offset info above and the time on your watch.

Other mounts (like my AP Mach 1) take care of the offset from the 75th meridian by asking me to input my exact longitude. The software then figures out the local sidereal time and points the scope as desired.

Helpful, I hope.

Dave, also in Toronto.

ps. what's a Polarie?

#12 DuiA1

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Posted 17 April 2013 - 08:20 PM

Vixen Polarie is a star tracker mount for DSLR. Here http://www.vixenopti...RIE Manual.pdf. I did just as you stated and with the 5 degree offset to the west on the polarscope dial, I still don't get the right orientation of polaris on the polarscope reticle when I dial in the EST. Thank you for confirming that the difference is 5 degrees west.






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