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iOptron Skytracker polar alignment question

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#1 Mako72

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Posted 03 February 2016 - 11:56 PM

I recently purchased an iOptron Skytracker V2 and want to try it tomorrow as it looks like the night sky will finally be clear. I'm new to astrophotography and need some help with doing the polar alignment on the Skytracker. I don't have a smart phone so I can't do the iOptron app for iPhones. I did find Michael Covington's excellent paper on doing the Skytracker polar alignment here: http://www.covington...hael/blog/1302/

 

I live in the St. Louis area (CST) so the lattitude for St. Louis is 38.627 degrees.

I want to try a 200mm lens on my Canon T3i with the Skytracker so I would like my polar alignment to be better than just sticking Polaris in the middle of the Skytracker reticle. If I understand Michael Covington's chart from the above link correctly here:

Reticle1.jpg

 

it means that during the month of February at 8pm, I should put Polaris on the 40 degree ring at 5 oclock on the reticle for proper Skytracker tracking as I have indicated here:

Reticle3.jpg

 

Will my Skytracker be correctly polar aligned for tomorrow night? Is it as simple as that? Thanks 

 

 

 

 



#2 bobzeq25

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Posted 04 February 2016 - 12:44 AM

Pretty much.  That will be close, maybe close enough.  There are a variety of small programs that give more precise numbers, don't know how much difference it makes.

 

Just be sure to check it immediately before exposing, it's really easy to shift it while pointing the camera.

 

You can see how well you did by checking it at the end of the exposures.  If you're still on the three rings, that's good.



#3 Mako72

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Posted 04 February 2016 - 01:00 AM

Bob, thanks for the reply.

That's good news.

I'm really looking forward to trying this tracker out tomorrow night.

I hope the cloud forecast holds up.

I should probably start out with a wide angle first but I really want to try out M31 first.

 

Regards, Charles 



#4 ChristianG

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Posted 04 February 2016 - 01:30 AM

Hi Charles.

 

Your little red arrow is on the right circle: currently Polaris is off from the North Celestial Pole by about 40 minutes of arc, or about 0.65 degree. And it moves on the little circle such that a given position occurs almost 4 minutes earlier every day. This is because there are 365.24 solar days in one year but 366.24 sidereal days, hence the 4 minute per day change: 1 part in 365.24. And since it changes by only this much every day, you can re-use the data for a few days, since it amounts to a change of about 1 degree around the circle per day...

 

If you want more info/precision on this, you can digest what's in this recent discussion...

 

http://www.cloudynig...airs-vs-circle/

 

By the way, with a 200 mm lens, if you limit your single shots ("subs" as they are called) to 30-60 s exposures, alignment does not need to be that accurate, since stacking software will take care of registering the different shots on top of each other. Assuming you want to stack many shots (20 or so for M-31 should do at first), which is recommended. Good luck and cheers!

 

--Christian


Edited by ChristianG, 04 February 2016 - 01:51 AM.


#5 Mako72

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Posted 04 February 2016 - 02:33 AM

Hi Christian,

 

I see what you are saying. In looking at the chart:

 

If on Feb. 1, the red dot is at 5 o'clock at 8pm, then for a more accurate polar alignment on Feb.15, at 8pm, one would position the red dot halfway between 5 and 4 o'clock. 

 

Thanks for the suggestions on shooting M31 with the 200mm lens. I'm really looking forward to using the Skytracker tomorrow night.

 

Regards, Charles



#6 S.Boerner

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Posted 04 February 2016 - 09:10 AM

A program called Polar Finder Scope (Polar 204) that has been around forever may be of help to see the "hour angle" you need to set:

http://myastroimages..._by_Jason_Dale/



#7 17.5Dob

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Posted 04 February 2016 - 11:50 AM

A program called Polar Finder Scope (Polar 204) that has been around forever may be of help to see the "hour angle" you need to set:

http://myastroimages..._by_Jason_Dale/

+1
That's what I use as well, no need to buy an "app".



#8 Mako72

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Posted 04 February 2016 - 12:45 PM

A program called Polar Finder Scope (Polar 204) that has been around forever may be of help to see the "hour angle" you need to set:

http://myastroimages..._by_Jason_Dale/

 

Thanks guys, I'll check that link out. 



#9 ChristianG

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Posted 04 February 2016 - 12:52 PM

Hi Christian,

 

I see what you are saying. In looking at the chart:

 

If on Feb. 1, the red dot is at 5 o'clock at 8pm, then for a more accurate polar alignment on Feb.15, at 8pm, one would position the red dot halfway between 5 and 4 o'clock. 

 

Regards, Charles

 

Unless I am wrong, a bit more than that. 14 days off means about 55 minutes earlier. So almost 4:00. Make sure you use 2016 ephemeris! Michael's article is 3 years old...

 

I get my data here:

 

http://www.cadastral.com/2016feb.htm

 

But it's for Greenwich longitude! Needs to be tweaked a a bit if you are halway around the world from there...

 

--Christian



#10 Mako72

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Posted 04 February 2016 - 04:16 PM

 

Hi Christian,

 

I see what you are saying. In looking at the chart:

 

If on Feb. 1, the red dot is at 5 o'clock at 8pm, then for a more accurate polar alignment on Feb.15, at 8pm, one would position the red dot halfway between 5 and 4 o'clock. 

 

Regards, Charles

 

Unless I am wrong, a bit more than that. 14 days off means about 55 minutes earlier. So almost 4:00. Make sure you use 2016 ephemeris! Michael's article is 3 years old...

 

I get my data here:

 

http://www.cadastral.com/2016feb.htm

 

But it's for Greenwich longitude! Needs to be tweaked a a bit if you are halway around the world from there...

 

--Christian

 

I was afraid of that. I had seen that it had a date of 2013 on it but thought that it would not make a difference.

To be honest, I don't understand the info on the link you provided yet, I'm new to this astro stuff. I guess I'll put Polaris at 5 o'clock on the 40 degree ring unless someone can suggest a better clocking location. I'm headed out the door in about 2 hours with a 1 hour drive to get to a darker location so I don't have the time to figure it out myself right now. I'll keep the exposures on the shorter side since my alignment won't be perfect and maybe I'll get some keepers.  :undecided:



#11 S.Boerner

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Posted 04 February 2016 - 04:31 PM

Just wondering... 

 

I'm over in Chesterfield and go to Whiteside or Danville for dark sky.   Over on the east side where do you go for dark sky?

 

Tks



#12 Mako72

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Posted 04 February 2016 - 04:41 PM

Just wondering... 

 

I'm over in Chesterfield and go to Whiteside or Danville for dark sky.   Over on the east side where do you go for dark sky?

 

Tks

Tonite I'm headed up north to a friends home. He's in a rural area with much better skies than where I am ( I live in a subdivision).

I have been to Council Bluff campgrounds in the Mark Twain forest. It is rated pretty dark and they have an area leveled out for astronomers. It's an 1 1/2 hr drive for me but I intend to return when I get this Skytracker figured out tonight.



#13 Michael Covington

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Posted 04 February 2016 - 04:50 PM

 

Hi Christian,

 

I see what you are saying. In looking at the chart:

 

If on Feb. 1, the red dot is at 5 o'clock at 8pm, then for a more accurate polar alignment on Feb.15, at 8pm, one would position the red dot halfway between 5 and 4 o'clock. 

 

Regards, Charles

 

Unless I am wrong, a bit more than that. 14 days off means about 55 minutes earlier. So almost 4:00. Make sure you use 2016 ephemeris! Michael's article is 3 years old...

 

I get my data here:

 

http://www.cadastral.com/2016feb.htm

 

But it's for Greenwich longitude! Needs to be tweaked a a bit if you are halway around the world from there...

 

--Christian

 

 

I will check that, but I'm inclined to stand by the original chart.  The full circle is 12 months, so half a month would be half of 1/12 of the circle.

 

I actually use Polar Scope Align Pro for the iPhone 5, which is slightly more accurate than iOptron's app and costs the same ($1.95) and haven't used my own chart in a while.  But Polaris has not moved enough since 2013 to affect things.



#14 Mako72

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Posted 04 February 2016 - 05:34 PM

 

 

Hi Christian,

 

I see what you are saying. In looking at the chart:

 

If on Feb. 1, the red dot is at 5 o'clock at 8pm, then for a more accurate polar alignment on Feb.15, at 8pm, one would position the red dot halfway between 5 and 4 o'clock. 

 

Regards, Charles

 

Unless I am wrong, a bit more than that. 14 days off means about 55 minutes earlier. So almost 4:00. Make sure you use 2016 ephemeris! Michael's article is 3 years old...

 

I get my data here:

 

http://www.cadastral.com/2016feb.htm

 

But it's for Greenwich longitude! Needs to be tweaked a a bit if you are halway around the world from there...

 

--Christian

 

 

I will check that, but I'm inclined to stand by the original chart.  The full circle is 12 months, so half a month would be half of 1/12 of the circle.

 

I actually use Polar Scope Align Pro for the iPhone 5, which is slightly more accurate than iOptron's app and costs the same ($1.95) and haven't used my own chart in a while.  But Polaris has not moved enough since 2013 to affect things.

 

Thanks Michael.

I give it a try at 5 o'clock on the 40 degree ring.

My son's been pushing me to get rid of my flip phone, looks like it's time! lol.

Truck is packed, headed out.

 

Charles 



#15 ChristianG

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Posted 05 February 2016 - 06:48 PM

Hi guys.

 

First--my apologies--I made a mistake in my message #9 above:

 

"Unless I am wrong, a bit more than that. 14 days off means about 55 minutes earlier. So almost 4:00."

 

My brain farted and I didn't realize that the the polar scope has only 12 divisions, but there are 24 hours in a day. So yes, 14 days means about 1/2 of an "hour" on the dial, so halfway between 4 and 5 o'clock. Why didn't they put 24 divisions instead, to match what is actually happening?

 

That said, it's not that hard to undestand Michael's chart in the context of the epehemeris data. Have a crack at it, you might be interested! As for 2013 vs 2016 data: they are so similar that differences can be ignored. For instance:

 

--In the 2013 ephemeris for February 1st (http://www.cadastral.com/2013feb.htm) Polaris is directly above the NCP at 18:00:07 (TUC on table), so 6:00 pm in Greenwich.

 

--In the 2016 ephemeris for February 1st (http://www.cadastral.com/2016feb.htm) Polaris is directly above the NCP at 18:06:52.7, so 6:07 pm in Greenwich.

 

Not enough of a difference for our purposes.

 

As for the difference between data for Greenwich and for St-Louis, you are about 6 hours difference from Greenwich, so events happen 1/4 of a day later than Greewich. Since Polaris events are earlier 4 minutes per day, the equivalent Polaris position with respect to the NCP where you are will be earlier by 1/4 of that, or 1 minute of time compared to the data for Greenwich, not a significant amount: Polaris doesn't move that much in 1 minute: there are 60 X 24 = 1440 minutes in a day, so it would be off 1/1440 th of the circle, or 0.25 degree in the sky!

 

As for the polar scope: Upper Culmination means directly above the NCP, this would mean at 12 o'clock visually. But since the polar finder scope inverts the image, this actually means at 6 o'clock on the circle.

 

So at 6 pm on February first, you put Polaris at 6 o'clock on the circle. Two hours later, at 20:00, put it at 5 o'clock.

 

On February 5th, Upper Culmination occurs at 17:51:02, so at 17:51 pm, put Polaris at 6 o'clock on the circle. Two hours later, at 19:51, put it at 5 o'clock. Would waiting for 8 pm instead of 19:51 make a difference? Not really.

 

Quantitative astronomy can be fun too!

 

--Christian



#16 Mako72

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Posted 07 February 2016 - 02:16 PM

Hey guys, thanks for the above information.

I was able to get some pictures with the Skytracker. As was suggested above, I kept the exposures shorter to cover up any misaligment errors I may have had with the Skytracker.

It was frustrating to line up Polaris and have it move as I tightened the lock down screw.

But I finally got it close and the pictures came out decent at least to my eye. Now for the post processing part but I'll leave that for another thread, lol.



#17 Alex McConahay

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Posted 07 February 2016 - 03:35 PM

You know, if you go to your local app store and search ioptron polar ....something, you will find what I believe is a free app that uses your phone gps and such to tell you right where to put Polaris.

 

I think it is free.....anyway.

 

Alex




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