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Tricky doing polar alignment?

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#1 mooresaw

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Posted 18 May 2021 - 09:47 AM

Hello

 

I am running my celestron CGEM II mount and noticed a recurring phenomenon this summer as I try to polar align...

 

My house faces 56o NE and I scope in the backyard, so Polaris is always obstructed until late at night. I align my mount to point north and set the latitude on the mount and do my 4+2 and then go to the All Star Polar Align.

 

I've been using Spica as it is fairly south, almost due south and not too low on the horizon. Earlier in the spring I used Regulus and Procyon  to polar align but in any event it I notice the same thing:

 

Picking the star and aligning it with the hand controller is no problem but the mount REALLY skews far away when aligning the mount. Often I have to adjust the Azimuth knob to the maximum and it still comes up short...I feel like this shouldn't be the case? Anyone else run into this? can I do something to offset this in the initial setup?

 

In the winter I didn't seem to have this problem, I'd just use Sirius and it seemed to go off without a hitch but I am wondering now if I accidentally had my scope setup facing south lol.



#2 mooresaw

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Posted 18 May 2021 - 09:57 AM

like is it ok to physically move the mount to achieve the polar alignment? that's a newb question I'm sure...



#3 Couder

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Posted 18 May 2021 - 10:09 AM

Without being able to see Polaris, it will be difficult to align. However, it doesn't look like you're doing photography, so you don't need to be perfectly aligned. Get or borrow a decent compass. Use it to roughly align with Polaris. do remember to set your latitude for your location. I have set up many times in the daytime using just a compass. Then at night, if I'm off, all it takes is a nudge with the buttons to re-center. If you're way off, either rotate the mount on the tripod if you can. Otherwise, you will have to be careful to move it without tipping it over. After you get it aligned to where you can live with it, try putting 3 pins or something in the ground so it will be easier next time. If you can't do that, pick a door frame, window, piece of siding or something to sight on to get it roughly aligned next time.



#4 spereira

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Posted 18 May 2021 - 10:13 AM

Moving to Mounts.

 

smp



#5 mooresaw

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Posted 18 May 2021 - 10:24 AM

I am doing some AP...I was under the impression the mount cannot be picked up and moved...but seems like it can?



#6 pyrasanth

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Posted 18 May 2021 - 10:27 AM

Make the pain go away- invest in the Ioptron Ipolar alignment camera- makes polar alignment a breeze- you don't even need to be able to see the pole star.



#7 rgsalinger

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Posted 18 May 2021 - 11:10 AM

I have to ask. Are you using a compass to find north? Is it possible that you are finding magnetic rather than true north? I moved from a location where the two coincided to a location where they are separated by 20 degrees. First few nights out, I could not figure out why Polaris was way way off. 

 

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#8 DuncanM

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Posted 18 May 2021 - 11:33 AM

Hello

 

I am running my celestron CGEM II mount and noticed a recurring phenomenon this summer as I try to polar align...

 

My house faces 56o NE and I scope in the backyard, so Polaris is always obstructed until late at night. I align my mount to point north and set the latitude on the mount and do my 4+2 and then go to the All Star Polar Align.

 

I've been using Spica as it is fairly south, almost due south and not too low on the horizon. Earlier in the spring I used Regulus and Procyon  to polar align but in any event it I notice the same thing:

 

Picking the star and aligning it with the hand controller is no problem but the mount REALLY skews far away when aligning the mount. Often I have to adjust the Azimuth knob to the maximum and it still comes up short...I feel like this shouldn't be the case? Anyone else run into this? can I do something to offset this in the initial setup?

 

In the winter I didn't seem to have this problem, I'd just use Sirius and it seemed to go off without a hitch but I am wondering now if I accidentally had my scope setup facing south lol.

Use google earth and identify a land feature that is due north (or south) of your setup spot and use that to orient the mount during setup. That should allow the use of ASPA with minimal need for azimuth adjustment using the PA adjusters.


Edited by DuncanM, 18 May 2021 - 12:53 PM.


#9 mooresaw

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Posted 18 May 2021 - 12:15 PM

I have to ask. Are you using a compass to find north? Is it possible that you are finding magnetic rather than true north? I moved from a location where the two coincided to a location where they are separated by 20 degrees. First few nights out, I could not figure out why Polaris was way way off. 

 

Rgrds-Ross

I use a compass app set to find true north. I set up the tripod, put the mount on throw the phonei n the dovetails and get it to true north and set latitude for my area. Then I put on the OTA and do the 2+4 and attempt the All Star Polar Align.



#10 starbug

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Posted 18 May 2021 - 12:55 PM

I just have to ask this quetion.  You wrote "My house faces 56o NE and I scope in the backyard, so Polaris is always obstructed until late at night". Polaris, however, does not move that much. So are you sure yuu're pointing at Polaris?


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#11 mooresaw

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Posted 18 May 2021 - 01:31 PM

I just have to ask this quetion.  You wrote "My house faces 56o NE and I scope in the backyard, so Polaris is always obstructed until late at night". Polaris, however, does not move that much. So are you sure yuu're pointing at Polaris?

It doesn't move much, If I move around the yard I can see it in between houses. The sunsets here 9:30 - 10 PM. I also have an esaement on my property, a 9 foot acoustic fence (YAY). So any where I set the scope up that could potentially see Polaris (will try again tonight) is usually blocking off much of the by being close to the back corner and close to the fence. Just because I can see it between the houses doesn't mean the scope can pick it up, I like being in the center of the yard for a wider FOV. I just feel like this is much harder than it has to be haha so most likely something I'm doing wrong.



#12 WadeH237

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Posted 18 May 2021 - 01:43 PM

Picking the star and aligning it with the hand controller is no problem but the mount REALLY skews far away when aligning the mount. Often I have to adjust the Azimuth knob to the maximum and it still comes up short...I feel like this shouldn't be the case? Anyone else run into this? can I do something to offset this in the initial setup?

Proper polar alignment is a physical positioning of the mount.  It doesn't matter how you do it, whether you do ASPA, drift alignment, PoleMaster, Sharpcap, or whatever.  If you have insufficient azimuth adjustment travel, it's because your mount was oriented too far away from true not when you tried to polar align it.

 

If you are really good with a magnetic compass, and understand the magnetic variation in your location, it is certainly possible to get really close on the initial setup.  But it doesn't take much error to exceed the azimuth adjuster travel.  When this happens, your only recourse is to physically move the entire mount, tripod and all, so that you are close enough for the azimuth adjuster to reach.  This is no big deal.  Most of us have to do it once in a while.  I have had to shift my couple-of-hundred-pounds rig by a few degrees before when setting up at a dark sky site.  Fortunately, it's pretty rare.  I have magnetic variation references for each of the sites that I use, and I have a compass that allows me to dial in the variation to find true north.

 

Once the mount is polar aligned, then you don't want to move it again.



#13 godelescher

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Posted 18 May 2021 - 05:28 PM

First off, ignore the people here who think your problem is solved by investing in new equipment. Nothing pleases the denizens of cloudy nights more than spending money.

 

Here's a link to the drift method of polar aligning you scope: http://www.astrosurf.com/re/polar.html

 

However, if you're viewing visually, North-ish works fine. I'd sell the $2000 goto mount and buy a $200 polaris for visual use. You'll be happier, see more, and have a bunch of money you can spend on things that actually matter


Edited by godelescher, 18 May 2021 - 05:29 PM.

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#14 rgsalinger

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Posted 19 May 2021 - 07:17 PM

Polaris moves in a circle around the pole that's less than 1 degree in radius every 23 hours and 56 minutes. So, it's not going to become suddenly visible as it revolves around the pole at a particular moment in time each night. So, I'm figuring that the issue is that you can't see it from your preferred imaging location at all.

 

If that's the case you have many options. If you are a visual observer, you should be able with the right magnetic to true north adjustment to get close enough for that use case. Then just do a 2x3 star alignment and you should find objects. What bothers me about this is that a CGEM supports the ASPA method of polar alignment documented here. That does not require being able to see Polaris at all. 

 

If you are imaging or just using a computer connected to the mount you can use PHD which is free guiding software but has an assisted drift alignment method that works quite well. That would be the bargain choice, IMHO.

 

Since you are having trouble seeing Polaris, using a polar scope of any kind is not useful. You've got a really nice mount but I think that your precise problem is (at least to me) not quite clear.

 

Rgds-Ross



#15 KLWalsh

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Posted 19 May 2021 - 10:24 PM

When you say ‘obstructed’ until late at night - do you mean you live in a very northern latitude and Polaris isn’t visible until late because twilight lingers long past 9 or 10 o’clock at night?
Because, as others have pointed out, Polaris barely moves. It’s practically in the same place all day long.

I have a CGEM on a backyard pier (no observatory yet), and I have a seasonal tree that blocks Polaris 6 months of the year. I aligned fairly close to Polaris and then used ASPA to fine tune the alignment. If your initial alignment is close, you should have plenty of adjustment with the azimuth knobs.

You should start with a star map or sky app on your phone showing the sky at night to be sure you’re on Polaris and not a nearby star.

#16 Phil Sherman

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Posted 20 May 2021 - 09:44 AM

.......

 

If you are imaging or just using a computer connected to the mount you can use PHD which is free guiding software but has an assisted drift alignment method that works quite well. That would be the bargain choice, IMHO.

 

.........

 

Rgds-Ross

If you're imaging, a free alternative to using PHD's polar alignment is to do a photographic drift alignment. This process takes a little over a minute for each measurement.

 

1. Rough align your mount using a compass and level.

2. Set your slew rate to 1x sidereal, your camera for a 70 second exposure, and point the mount to the first alignment point, the celestial equator near the meridian. Disable guiding.

3. Start the exposure. Let the mount track for 5 seconds then slew E for 30 seconds then W for 35 seconds.

 

Your image should show bright stars (the 5 second tracked portion) with a "V" shaped tail. Adjust the mount using the azimuth adjustments and repeat the test until the 'V' collapses into a line that passes back through the star. Repeat this process at the second drift alignment point, 25-30° above the E or W horizon along the celestial equator to adjust the altitude of the mount.

 

If you level the tripod before attaching the mount, it will decouple these adjustments. If the tripod isn't level, the adjustments will interact and you'll need to do more than one iteration of drift alignment to properly align the mount.



#17 starbug

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Posted 21 May 2021 - 01:33 AM

Not sure how familiar you are with geometry, but if you have a spot where you canalign your mount using polaris, you can relatively easily translate the position/orientation of the tripod to any spot using the parallelogram principle, like the old drawing machines did. Leveling the tripod is essential, but should not be a big deal.



#18 duck

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Posted 21 May 2021 - 10:48 AM

I made a template with my latitude so that when placed against the RA housing the top surface is level.  Then I use a small carpenter's level to set the altitude (where did this term come from.  It's elevation.  Altitude is measured in units of length.)  There's a method on the internet to set the azimuth alignment in the daytime using the sun's shadow.  However, if the declination of the sun can be set accurately on the mount, the azimuth alignment of the RA axis can be set by pointing at the sun.  This stuff can be done in daytime.  Once stars are visible, use the drift method to improve the azimuth alignment.   




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