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t0ny

How easy should Polaris be to find through Polarscope?

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Havingg read and followed this thread I am really glad I bought a dobsonian mount. But I do understand the need for this alignment especially if AP is involved. Is there any mileage in using an app on a mobile/I pad to find Polaris thereby removing any doubt as to which star you are looking at to align the mount ?

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Polar aligning is really easy and takes a minute when you know how. A well aligned equatorial mount is great to use once set up. Like all these things it is a learning curve and a little practice. 

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Please pardon my apparent blunt tone, but getting on Polaris is not difficult.

1.  Buy a magnetic compass.

2.  Call the nearest airport, or check Google to determine the magnetic declination for your area.

3.  Using the compass (with magnetic decclination applied) determine the line of TRUE NORTH.

4.  Set your tripod with the "north leg" directly point at TRUE NORTH (as determined above).  You can validate this by using the compass to check that the two back legs are lined up east/west (again, with the mag dec applied).

5.  Now, that your tripd/scope are pointing to TRUE NORTH, simply set your latitude on the latitude scale.  This will point your scope directly at the North Celestial Pole which can be at most 0.7o from Polaris.  The star that should be centered in your eyepiece is Polaris.  If you have to adjust anything, only move the azimuth screw(s) on the MOUNT, and/or only move the latitude adjustment.  DO NOT MOVE THE SCOPE RA or DEC.

Lastly, use the polar alignment scope to get Polaris in the tiny circle that is etched in the lens.  AGAIN, do not move the scope... just the mount.

Clear, Dark Skies

Good idea, great idea actually,  but - 

Tripods and scopes &c are usually metal. Any metal can throw a compass off especially the ferromagnetic ones: iron, nickel, cobalt, (forget gadolinium because it's liquid at room temperature) and then aluminium and a few others can repel a magnet, and any electric current generates a fairly strong magnetic field. Electric motors invariably contain magnets, bad enough but if they run then you get really strong swirling magnetic fields.

If I'm on the patio in the back yard there's an old well underneath the paving slabs somewhere with a cast iron grating cover, the magnetic compass goes haywire.

The iPhone has a compass, not sure if other mobiles do, it only shows magnetic north but it does show lat and long. Not sure how accurate GPS is these days but it's good enough.

So, off to iTunes Store and yes there are True North Compasses available :grin:

In the UK we do not need to phone an airport (to be put on hold) we have Ordnance Survey Maps which show us deviation of magnetic north from true north, it's in the corner of each OS map.

This UK site may be of use to find exactly where we are https://www.ordnancesurvey.co.uk/gps/transformation

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Btw in the UK declination of magnetic from true north currently 1° 7' west

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Wikipedia says it's "the 45th brightest star in the night sky" it's just in that small part of the sky it's the brightest and located in a useful spot.

Well yes to the naked eye it is but once I bring up the binocs or finder there's a veritable salt pot peppering of the pesky things, now which one is it?

Use the Plough's pointers and it's bracketed by the second Vee of Cassiopeia's "W" and on the end of Ursa Minor's tail.

I think the finder needs a gun sight to get ball park.

I don't know if it obvious but Polaris isn't on the pole, it orbits in a small circle. So we have to know where it is supposed to be at any given time and align on that.

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Well yes to the naked eye it is but once I bring up the binocs or finder there's a veritable salt pot peppering of the pesky things, now which one is it?

Use the Plough's pointers and it's bracketed by the second Vee of Cassiopeia's "W" and on the end of Ursa Minor's tail.

I think the finder needs a gun sight to get ball park.

I don't know if it obvious but Polaris isn't on the pole, it orbits in a small circle. So we have to know where it is supposed to be at any given time and align on that.

Yes my point was really that I thought the OP was expecting Polaris to be a noticeably bright star, like the brightest star in the sky.  My point was it isn't. - but star hopping like you say is the way to go and then a rdf helps get it pointed right (for which you need to be able to spot the constellations - not as easy in urban LP conditions as you might think  :mad:  ). - other's methods of working out the approximate position from compass and latitude probably works but I like my way better - less hassle.  Anyway, you need to know the constellations when you get to the next step - 3-star alignment.

I don't know if it obvious but Polaris isn't on the pole, it orbits in a small circle. So we have to know where it is supposed to be at any given time and align on that.

perhaps not immediately obvious but anyone who doesn't know it needs to read up some more on polar alignment (e.g. start with reading the manual for the mount).  OP was concerned about getting polaris in the fov of the polarscope at all, so worrying about the hour angle comes next (and the HEQ5 handset will tell you that) - however it might not even necessary if you do a few iterations of the polar alignment routine with the handset software.

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Yes my point was really that I thought the OP was expecting Polaris to be a noticeably bright star, like the brightest star in the sky.  My point was it isn't. - but star hopping like you say is the way to go and then a rdf helps get it pointed right (for which you need to be able to spot the constellations - not as easy in urban LP conditions as you might think  :mad:  ). - other's methods of working out the approximate position from compass and latitude probably works but I like my way better - less hassle.  Anyway, you need to know the constellations when you get to the next step - 3-star alignment.

perhaps not immediately obvious but anyone who doesn't know it needs to read up some more on polar alignment (e.g. start with reading the manual for the mount).  OP was concerned about getting polaris in the fov of the polarscope at all, so worrying about the hour angle comes next (and the HEQ5 handset will tell you that) - however it might not even necessary if you do a few iterations of the polar alignment routine with the handset software.

Yes indeed.

But I don't have an HEQ, I have a Star Adventurer with a little disc on a graticule which you have to hang upside down like a bat to see. Motorised equatorial mount (EQ) can't use 3-point, polar align only: these things used to be wind-up clockwork.

By comparison the 3-point on the 130SLT is a doddle (or 2-point, or even 1-point if needs must)

Now, for Polaris there are indeed cool Apps for aligning on it because it so does not go in the centre of the finder but on the ring at the hour angle which in turn should be set for date and time offset. The latter bit is read the manual :eek:  The App I was recommended from SGL is "PolarAlign" of which two versions by GV out there, I find "Astro-Physics PolarAlignAP 2.1" can find our location on the GPS but sibling "PolarAlign 5.1" cannot. The latter is as much use as a chocolate teapot but the former is dead simple and works really well.

If you use the Star Adventurer manual method then you have to set the date on a dial not calibrated in days and then set the time offset and the hour angle and keep it time adjusted whilst dancing around the rig by the light of the moon: you then align Polaris at the 6 o'clock position.

If you use the App then you turn the graticule upright and aim Polaris to the position on the circle indicated: this still means hanging upside-down or rather kneeling on a wet deck with a craned neck. With my spondylitis this means arranging the tripod so I can best get at the eyepiece; that means I can't have a "north leg". I need to fashion a tube hood for the finder because I have an inconvenient street lamp at home, or stick a photo brolly on a stand :cool:

The native iPhone Compass App is nice but I cannot tell whether it is true or magnetic north, there is only 1° 7' declination here and these compass Apps jiggle about. My magnetic compass points to the motor in the Star Adventurer, not ok. There are other iPhone Apps but most look like some steam punk nightmare, I need easy to see and read in the dark, that means BIG numerals please if you ever read this.

So having set the alignment accurately on Polaris at a dark field site, I should only need to align it with a compass other than checking or if it is not tracking.

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Good idea, great idea actually,  but - 

Tripods and scopes &c are usually metal. Any metal can throw a compass off especially the ferromagnetic ones: iron, nickel, cobalt, (forget gadolinium because it's liquid at room temperature) and then aluminium and a few others can repel a magnet, and any electric current generates a fairly strong magnetic field. Electric motors invariably contain magnets, bad enough but if they run then you get really strong swirling magnetic fields.

I wasn't clear in my post.

When I referred to establishing a line, I meant with the rig removed... the "line" (for me) is a piece of tape laid down north/south.

I do my backyard alignments on a concrete pool deck that is filled with rebar and God knows what else.  Obviously, one doesn't fool around with a compass near ferrous objects. :rolleyes:

Clear, Dark Skies

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I also spent my first effort at polar aligning crouched on the floor staring up a polar scope with the counterweight pole in the way! It was also a total disaster as well, don't lose heart. You should also ensure that the polar scope is aligned with the mount, and this can be done during the day - I found astronomyshed's youtube videos for the NEQ6 very useful. The advice to dim the illumination is spot on. You can't see anything with it on full glare. Mine is right down.

These days, my setup is pretty streamlined. Put in date/time, and because the mount it pretty close form the time before in terms of altitude, Polaris is obvious. I think you were off in terms of the latitude and this caused the issues (once the bbar was moved out of the way!).

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I wasn't clear in my post.

When I referred to establishing a line, I meant with the rig removed... the "line" (for me) is a piece of tape laid down north/south.

I do my backyard alignments on a concrete pool deck that is filled with rebar and God knows what else.  Obviously, one doesn't fool around with a compass near ferrous objects. :rolleyes:

Clear, Dark Skies

Yes, that makes complete sense :grin: and please do not for a moment think I was criticising you or anyone else, I thought it a good idea, just throwing more ideas up;

Right pond an airport is not going to help and may refer you to security :eek:

The iPhone is not bothered by magnetic fields but does seem to be bothered by electrical fields and we can get a "move away from interference" message. Folks are more likely to have a mobile in their pocket than a compass.

Wife is so not going to let me inscribe lines on the patio even for "her" telescope; I'm not lifting the slabs to find the well spring but can hear the stream below which feeds into a storm drain under the street now.

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my tripod mark so getting back in same place were small indents made with a masonry drill so the tripod feet dropped in them......they have faded now back to the normal colour....

2012-02-25124200.jpg

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I've been astro-ing for a few years now, and I STILL can have a spot of bovver with finding Polaris, sometimes. It's not actually that easy.

  • I make sure that my Alt scale is at 52 degrees, after adjustments last session - NOTE: it's in 2-degree increments, not one!
  • I level the mount with a spirit level (there's no integral one) to make sure I'm not tilted forward or back.
  • I have a brilliant stick with an attached compass that a friend did for me - but try the suggestions on here to find north.
  • If I'm having a bad night and still can't find Polaris (not often now) I attach a laser pointer to an old tripod using duct tape then find Polaris through the polarscope using the beam.

Good luck!

Alexxx

Edited by Astrosurf

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Those who have been observing for some little time, the brain should remember some of the star patterns for the Constellations and of course the position of Polaris in relation to Cassiopeia and Ursa Maj, your eyes should locate it without hesitation and its relation to Constellation member stars Kocab, Pherkad etc, depending on your quality of seeing of course, If not, then give it a bit of practise, observing for just few minutes every clear night, the same goes for the major Constellations, if you are unsure. If you now invest in a decent RDF with a good mirror window and centre it in with your finder scope cross hairs. There should be no further problem, as you can now put your system onto Polaris with both eyes open, this goes for anything else you want to star hop from, for those that are manually finding your way about the sky that is :)

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I had to check acronym RDF in the sticky since the commonest meaning is "Radio Direction Finder" not "Red Dot Finder" but the olde marine and aircraft radio beacon systems are obsolete having been replaced by GPS.

- not many people want to know that  :wink: 

On wedge scales -

The Star Adventurer scale for example is marked in 3° increments (there are 5 marks between 45° and 60°) but it is possible to set it within 0.5° by interpolation, you estimate where the third divisions are and then halfway between that. However the scale is probably not be particularly accurate in the first place; having worked a calibration laboratory for years, I consider it to be "For Indication Only" as labelled on anything not calibrated.

We are about 51.5°N here but Polaris got aligned at 54° on the scale. So don't set the scale and expect to find Polaris spot-on.

It can be a pain finding Polaris. The southern sky can be crystal clear but the north veiled in cloud. If you have sufficient patience the north may clear and the south will then cloud over.

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Hope t0ny doesn't mind my asking a dumb question on his thread but it is related:

I hope I'm right in saying that the HEQ5 polar scope gives an inverted (i.e. upside down but not reflected) image, so my question is: do I need to get the diagrams of Cassiopeia and Ursa major to match what I see in the sky (correct way up), or inverted (upside down)?

Am assuming I put Cassiopeia to the west and Ursa major to the east (as they are at present around 8pm UK), with 'upside-down' Polaris in the middle.

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The Plough's pointers (Ursa Major) are the olde skool method of finding Polaris but Cassiopeia's lopsided "W" is usually brighter, it is further away than The Plough.

Being lopsided it should be easy to check it it is right way up or base over apex in the scope.

Charts and planispheres usually "what you see" with naked eye, we invert them on the fly.

Patrick Moore and Pete Lawrence "The 21st Century Astronomer" ISBN978-1-78177-125-9 is well worth a read anyway and has a nice set of charts in the back and a big pull-out sky map

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Hope t0ny doesn't mind my asking a dumb question on his thread but it is related:

I hope I'm right in saying that the HEQ5 polar scope gives an inverted (i.e. upside down but not reflected) image, so my question is: do I need to get the diagrams of Cassiopeia and Ursa major to match what I see in the sky (correct way up), or inverted (upside down)?

Am assuming I put Cassiopeia to the west and Ursa major to the east (as they are at present around 8pm UK), with 'upside-down' Polaris in the middle.

This realy confuses me too so I tend to rely on the "polar finder" app that shows polaris as seen through the polarscope if I require more accuracy then I use the polaris hour angle in stellarium remembering that the 24hr clock zero hour is at the bottom.

Alan

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Hope t0ny doesn't mind my asking a dumb question on his thread but it is related:

I hope I'm right in saying that the HEQ5 polar scope gives an inverted (i.e. upside down but not reflected) image, so my question is: do I need to get the diagrams of Cassiopeia and Ursa major to match what I see in the sky (correct way up), or inverted (upside down)?

Am assuming I put Cassiopeia to the west and Ursa major to the east (as they are at present around 8pm UK), with 'upside-down' Polaris in the middle.

Just position them as they appear in the sky for a rough alignment.

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Thanks - have got PolarFinder going for Polaris itself, but putting Cassiopeia and Ursa major in the right places helps me find Polaris - and then get it into the circle etc.

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How about pointing your camera North and up a bit, take a pic. of say 5 second exposure to get plenty of stars. Then take several longer exposures to get star trails that will revolve around the north star. Lay one over the other, North star inentified. Would that work?

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If you have a Synscan Handset do a 2 star align, then a Polar Align using any star that easy to see, do this 2 or 3 time with different stars and your be as near as your ever get.....

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The scale can be out on the mount. Bit of trial and error should sort this. You won't be more than a couple of degrees out. It's the left right bit that usually puts Polaris out of view in the polar scope once you've got the right latitude dialled in. Like the idea of the camera right angle finder though. Very useful tip. Persevere, make sure you level the mount. Mark its position if you can. I have mine on three small paving slabs set in the lawn. Eventually it will be a 2 minute job.

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The scale can be out on the mount.

Good point, as can the bubble if you have one.  

Make sure your polarscope is orthogonal with the polar axis of the mount.  I think this has been described above and can be done in the daytime.

PA is only easy when you have conquered it, up until then it can be really difficult for a beginner especially if you happen to have an unlit reticule as I had in my first mount.  

Prize tricks, forgetting to rotate the dec axis, or forgetting to lower the counterweight bar and wondering why i can't see anything Duh!

Carole 

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