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I am still very new to this hobby and have run into a situation where my goto is consistently off by 8 to 10 degrees. Is this a problem with not finding true north.  Can I enter a different value to correct for this? Any suggestions would be appreciated.

 

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Hello Older Padawan, and welcome to SGL.

If you tell us which type of telescope system you have, perhaps one of our members with the same, or a similar, system could give you a few suggestions. Each system has slightly different requirements to get good initial alignment.

Geoff

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4 hours ago, Older Padawan said:

I am still very new to this hobby and have run into a situation where my goto is consistently off by 8 to 10 degrees. Is this a problem with not finding true north.  Can I enter a different value to correct for this? Any suggestions would be appreciated.

 

When using a magnetic compass you simply add or subtract your local Variation to find true . If you have west variation subtract and add for east. 

Also be aware of Deviation this is where a magnetic compass will be attracted by metal objects electrical interference near to it i.e telescopes and mounts power cables etc.

Magnetic north is continuing east year by year. If you are in the UK its not very much in the SW at the moment. Here is a link to a useful table. I don't think that variation will account for you 8-10 deg maybe 1 or 2 deg (again depending where you are)

https://www.ordnancesurvey.co.uk/blog/2019/03/magnetic-north-continues-its-march-to-the-east/

Steve

Edited by Steve Clay
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4 minutes ago, Steve Clay said:

When using a magnetic compass you simply add or subtract your local Variation to find true . If you have west variation subtract and add for east. 

Also be aware of Deviation this is where a magnetic compass will be attracted by metal objects electrical interference near to it i.e telescopes and mounts power cables etc.

Magnetic north is continuing east year by year. If you are in the UK its not very much in the SW at the moment. Here is a link to a useful table. I don't think that variation will account for you 8-10 deg maybe 1 or 2 deg (again depending where you are)

https://www.ordnancesurvey.co.uk/blog/2019/03/magnetic-north-continues-its-march-to-the-east/

Steve

Just noticed you are in Colorado so could make a significant difference.

Steve 

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If u mean your alignment stars being off by that and then u have to center it and push ok or align?

In that case 7 or 8 degrees is good I have gotten wider 10 to 15 degrees off.

I think its normall. The computer is just going off by the time date later and long it's not gonna be closer than that.

That's y it needs u to align on 1 2 or 3 stars to get 100% in the ep

Joejaguar 

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Just sight on Polaris and you won't be far off true North.    🙂

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Thanks for the input everyone. I have a Skywatcher 250P 10" with a SynScan GOTO and I am in Colorado. I have been using the 2 star alignment I think I will use Polaris next time and see if that takes care of the situation. I love all there is to learn about this hobby and I love the information on the site.

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As was said by Peter use Polaris. For visual that will be adaquate and the Synscan should be able to account for the difference.

Do you have a polar scope with the mount. If so then the next task is working out how to perform the polar alignment better with that and Polaris.

Polaris is something like 1 degree off of True North. I have seen values of 0.8 degree and 1.2 degrees. Not sure which one it actually is but 1 degree is in the middle.

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I agree start off with Polaris aligned first and do the 3 star align . As mentioned true north is less than 1* off center . 

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when i used to set up in the garden, I used to do an 3 star align,then pick a star[in named stars] slew to a nice easy bright star see where that was in a low power E.P centre in a high power E.P,then realign the scope and go to the star that was used to see where it in the low power E.P it should be near the centre but to improve the goto add 3 extra re-align stars and this should bring the star bang in the middle of a low power E.P. it seems long winded but its really worth it. Des

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Older Padawan

First of all welcome from Land Down Under

If you are not aware, we actually have three Norths, where I am South

1. True North, which is the line drawn along the meridian  between North and South Poles

2. Magnet North  This is the direction a compass points towards the Magnet North Pole

Depending on where you are on the earths surface, Magnet North can be either East or West of true north

Where I am, magnetic north is 12deg east

3. Grid North This is the direction of lines drawn on a map

Before adaption of GPS, we all used to use a street directory to work out where we wanted to go

The lines drawn on a street directly run North/South, East/West

The top of the map is always North

On a geographical map, in the margin, there is printed a 5 pointed star showing grid north, and magnetic north

What I have to do, when setting up my ED80 with my EQ5Pro mount, is face the North leg of mount south, then use a compass, allowing for magnet variation to set mount facing south

Then do a two star alignment

You will find what you been doing with two star alignment, once have base of your Dob aligned to true north, be more accurate than relying on alignment with Polaris

Hope everyone is more knowledgeable now with respect to different types of north

John

 

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I haven't had a clear night lately but I have found out the compass I was using was messed up. It would show a different north each time I tried to use it. Sometimes off by as much as 15 degrees. Obviously I no longer use that so next time out I will use Polaris and go from there. Thanks for all the help it is greatly appreciated

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I just got in after a couple of hours gazing at the universe and I have to say thank you guys all of you. I lined up on Polaris then did a 2 star alignment and it worked great. I was very close to dead center on everything I went to. Man I love learning from experienced people.

 

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On ‎02‎/‎12‎/‎2019 at 16:09, Older Padawan said:

 I have a Skywatcher 250P 10" with a SynScan GOTO and I am in Colorado. I have been using the 2 star alignment I think I will use Polaris next time and see if that takes care of the situation.

It looks like we both have the same system; mine has the extending optical tube. The good news is that you do not have to find North; it is much more important to have the base level. I have added a bubble level, and use a small wedge under one of the feet to get the bubble in the centre. With the base level, the cross-axis errors are effectively eliminated.

I use "Brightest Star" 2-star alignment, and this works well at dusk, when only the brightest stars are visible - avoiding the error of picking an adjacent star. If the planets Venus, Jupiter or Saturn are visible at a sensible altitude, the Brightest Star option will give these for a very simple 'Planet + 2-star' alignment, with an auto-slew to both stars. 

I used the free (on PC) planetarium program "Stellarium". By advancing time, the program adds the names of the stars that would be visible as the light fades. By changing date and time, I produced a table of 14 of the brightest stars, visible from my back garden (avoiding trees, fences and houses), for dusk in the middle of each month of the year. For each month, I highlighted 3, 4, or 5 of these stars, with the aim of having them separated by about 90 degrees in azimuth and 30 degrees in altitude (and in an altitude range between 20 and 75 degrees). For these stars, I noted the rough direction (N, NW, W etc.) and the altitude angle (the mount has an altitude scale, that should be accurate if the base is level).  This is where a few hours homework, on a cloudy night, will save you several minutes each time when the sky is clear.

As soon as you can see the first star with the naked eye, you can manually set the mount to the required altitude, and standing behind it, slew to line up the rough azimuth. This should get the star visible in the finder, and with small adjustments, in the eyepiece. Once centred, the mount suggests the second star. This is where the table is handy, to avoid stars hidden by your surrounding structures; and by having the base level, the Synscan software should make an accurate slew to your chosen second star, with it visible in the finder or even in a 25mm eyepiece.

I find that if I do the alignment at dusk, I can leave the mount tracking, go in for tea and a warm-up, and wait for the sky to get really dark. When I come out again, the final alignment star is close to the centre of the eyepiece.

For me, at 51.4 degrees N, Vega is a good target as a first star from October to January, and May to July. This is the star that I can pick out first as the Sun sets. A good alternative is Arcturus, which works for me from April to October.

If the sky is fully dark, Vega and Arcturus are obviously very bright in a 10" OTA, but I also use the double stars Mizar and Pollux.

Geoff

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Thanks Geoff some great information. I do have the 250P flex tube and after many frustrating nights of horrible alignment I went to Polaris and then did a 2 star alignment from that point. It worked really well as the scope slewed right where it was supposed to the rest of the session. I like your idea of preplanning with Stellarium and finding stars that aren't hidden from view by local obstacles. I will be putting that method into use immediately

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Hi and welcome to SGL.

The key to getting the alignment right is to not rush.  Accuracy in everything is what counts, the better your accuracy, the better the alignment.  This goes for every scope that I've used or helped with.  The same basic things work for me every time.

1. use Polaris (I've no experience in the southern hemisphere) as the point to set your tripod up, making sure that you align the north so that is points to polaris, that's always good enough.

2. setup the tripod, and make sure that it's level "BEFORE" adding the EQ head (if it's an EQ scope).    Getting the Alt-Az platform level will help when it comes to the polar alignment phase.

3. Add the EQ Head, and if you have a polar scope, now is the time to use it to get polaris roughly centered in the FoV.    (I use a guide scope to do PA, so there's still no need to 100% perfection at this point)

4. Add Telescope, and other stuff that you are going to be using for that session.  Balance the scope at this point.

 

For Manual equipement only (no camera and computer involved)

5. go back to the polar scope and make sure that the hour angle is set correctly.

6. use an app on your phone to figure out where polaris should be in your polar scope FoV, then adjust the mount.

7. put the telescope into it's correct home position.

8. do a 2 star alignment (or whatever works best for your scope)

 

 

I personally have two telescopes one is a goto scope, which I control from a laptop.  For this I use SharpCap Pro to perform a polar alignment.

For the other telescope I have an ASI Air, and use the polar alignment tool in that.

Both ways work roughly the same way.

 

1. turn on guide scope camera and attach to the software.

2. use the PA tool in the software.

3. the software will platesolve the camera location.

4. rotate the scope manually 60-90 degrees

5. platesolve the new location

6. move on to the correction phase

7. use the alt-Az knobs on the mount to shift the scope by the distance indicated to correct the PA error.

8. Repeat this, to double check that it's spot on.

9. use the scope for the rest of the night without worrying.

 

With my two scopes,  (one is a 51mm refractor, the other is an 8" SCT) following these steps gets me great polar alignment every time.  Actually until I switched to using SharpCap or the ASI Air to do the PA my aligments were generally not good.  The software has improved things no end and makes life so much easier.

 

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