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3 star alignment - suggest stars to choose


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Hi guys!

Can someone recommend which three stars should I choose while aligning my telescope? SynScan Go-To manual says:

  • One Star: Choose a star closer to the Celstrial Equator (smaller declination absolute value).
  • Two Star: Choose two stars that are on the same side of the meridian, and at least 3 hours apart in RA and 3° apart in Dec. If you suspect that the polar alignment is off by 1° and above, choose two stars that are well more than 3° but less than 60° apart in Dec.
  • Three Star: For the first two alignment stars, follow the same guideline as choosing for the Two Star Alignment. For the third alignment star, choose a star that is on the opposide side of the meridian of the first two stars. Both first alignment star and third alignment star should have an absolute value of 30° to 70° in Dec. If the first chosen star has a small Dec (<30°), the Dec of the third star should be at least 50°. The following formula can be used as a guideline when determining the correlation between the first and third stars in Dec:
    140°>Abs(Dec1)+Abs(Dec2)>60°


I live in Lithuania, my coordinates are roughly 55°N, 24°E and from my window these nights I can clearly see Regulus, Pollux, Castor, Capella. What stars comply with the given formula best knowing my location? Of course when I go outside the city for better sky, I can choose from whatever stars are visible from 55th parallel North, so what are the best three stars out there for best accuracy?

Edited by Thelonious
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In reality you can use any 3 stars.

However your alignment and therefore tracking will be best if you use stars spread across the sky and not just 3 stars in the same area.

We can only use what we have access to and to get the best you can try to use 3 well spaced out stars at varied heights in the sky.

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......I'm very new to astro having got an EQ6 in Feb/Mar this year.

......When I first tried to set it up, I ran into a similar issue - I knew the name & location of two stars - one of which I had used for polar alignment (Polaris!) & the other was in Orion & below the horizon........this made 3 star alignment a bit challenging ;-)

.......luckily for me, I had a laptop close to hand & a mobile broad band connection so I started looking up the star names givne to me on the mounts handset - it was a slow process. Half way through I realised I had planetarium software on the laptop - & that was much quicker!!!

Next time out I had printed up sheets of the major over head constellations with the star names on, plus I had a list of star names & their constellation in both star name order & a separate list in constellation order. This helped alot.

In the space of a couple of days i decided to memorise the major stars i could see, plus all the stars in the plough. this helped even more.

.......I recently moved to full laptop control over the mount (using ASCOM) & it is now a breeze doing the alignment - click on a star in the planetarium software & select 'slew to' - nudge it into the center using the controls on the laptop & 'accept'. Select next star on the planetarium software & repeat. It is much faster & you can pick stars on the same side of the meridian easily (meridian is drawn in the software). It is so much faster, & you are not limited to 'only' 3 stars if you want to do more. Note that the first star is usually a fair bit out - I was alarmed at this initially, but subsequent stars are far more accurate, often need little or no nudging to centrally align (must be my good polar alignment ;-) - joke!!!)

It is a bit of a learning curve going to full laptop control, but it is worth the short term pain - I can recommend it!

......sorry if this does not direct answer your question......when I was manually selecting stars from the handset, my choice was usually based on those that I knew or could find on my list. For me those in the plough proved convenient, but may not be separated far enough apart for really critical work, but it was good enough for me.

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.......I should maybe add that the plough (part of Ursa Major in case 'the plough' does not translate too well into your country) is pretty much over head for me, & I've only been imaging over head, so picking stars relatively close together over head has not presented too much of an issue.......& now I am autoguiding, it is even less of an issue.

So before I went laptop, I used to use Alkaid &/or Alioth (as they are both close to each other on the alpha sorted star list on the handset), then Mizar &/or Megrez &/or Merak. & Then maybe Dubhe - but I'd try & pick only from the same side of the meridian. I found this saved handset button pushing time (picking stars close together in the list) & it saved slewing time........occassionally I'd pick an out lying star, maybe Caph in Cassiopia, or something like that - almost as a 'test' to see how good the alignment was (or wasn't!). It may not be the best way to 3 star align, but for me it was okay & speeded up things a bit - but I tend not to whizz about the sky every few mins - I've pretty much limited myself to what is almost overhead to image - going through less atmosphere that way, & as I've been imaging, I tend to be glued to the same patch of sky for most of the evening so tracking accuracy rather than goto accuracy has been more important to me.

I don't know how your handset star list compares to mine on the EQ6 - maybe yours is sorted differently than mine.......maybe you know more star names than me (not hard!).

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Doesn't your manual also go on to say:

"In the Synscan version 3.10 or later, these criteria is implemented in the software. The list of alighnment stars contains only the appropriate stars"?

I will also be trying PAE to see what difference it makes but to be honest, I use an illuminated reticle to 'centre' the stars on a 3 star align and the mount is pretty much 'spot on' after that.

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To: m.tweedy - now that link woudl have been VERY handy to me mid March!!! ;-) I ended up making my own verison up!! Still, don't need it now I control the mount from Carte Du Ciel planetarium software & feed the laptop images from both DSLR & guidecamera & use those to center everything up.......

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Thanks guys! Chart in m.tweedy's link is very useful.

I've now got to known most of the constellations and their brightest stars that I see every night from my window. Those that are not visible will have to wait when months change and they drift into my view. :)

So there is no real problem of not recognizing the stars as I usually take my smartphone with planetarium app to my observing nights. But regarding the choice of three stars for the "triangle" they cover, would this choice for example be a good one for a start? The triangle covrs some eight constellations and parts of something like another five or six constellations. I presume accuracy is best withing the boundaries.

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Thelonious,

You don't say which version of SynScan you have, if it is above 3.10 then the software sorts out the stars for you so that, by the 3rd star, your choices might be more limited in order for you to be 'within the boundaries'.

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.......isn't that choice of stars going to give you a potential issue?

Vega is on the other side of the meridian to Spica & Capella.

I just put your location into a planetarium, turned on the meridian, turned on star & constellations & 'looked' at your sky.

Everything I've read, suggests using 3 stars from the same side of the meridian for alignment.........but that could be because I am trying to image & have to worry about things like backlash in the gears as the head moves over the meridian.

If I change sides of the meridian during the evening, I would consider re-doing a 3 star alignment on 3 stars just on the new side of the meridian before I started imaging.

......I guess if you are visually observing, you don't have to worry so much.

......capella looks very low in your sky for me to want to use it as a guide star though......

.......maybe others with greater experience might comment further as I'm new & learning too......

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Interested - what you have advised has probably just answered an puzzle I always had with teh handset when I used it - why the suggested alignment star list would change while I was using it - I never worked that out, & now it doesn't matter as I don't use the handset! ....but thanks (mine is the latest firmware I believe).

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I've just checked it today and the version is 3.27 so the feature of selecting best stars for aligning should already be implemented.

Yes.

I have noticed that if I pick a different 1st star for alignment then the subseqent choice of stars (I always do a '3' star alignment) changes. I assume that is because the SynScan software is keeping alignment within the boundaries it sets.

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