Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.

sgl_imaging_challenge_banner_solar_25_winners.thumb.jpg.fe4e711c64054f3c9486c752d0bcd6f2.jpg

Recommended Posts

POLAR ALIGNMENT IF THE POLE STAR IS OBSTRUCTED (e.g. OBSERVING ON A S-FACING BALCONY!!!) Set up your scope on the floor (assuming it's reasonably level) in equatorial mode, with a rough guess at North. Put the tube into whatever 'home' position the instructions specify, or that you have chosen. Now choose an easily recognisable bright star at mid altitude. Pretend you HAVE polar aligned, and tell the scope to go to this star. When the slewing stops lift the scope very gently and turn the mount round till the star is in the centre of the field of view and you should have a fairly good polar alignment. If you are for example videoing planets and can also autoguide, this alignment may be all you need. But you can now refine it by the drift method if you need to - see https://www.skyandtelescope.com/astronomy-resources/accurate-polar-alignment/ This method should be quite useful for Southern hemisphere observing, where the 'south pole star' - Sigma Octantis - is difficult to find especially in light polluted skies. And of course my advice here applies if you have a North-facing balcony!

 

Edited by Sun
Extension of advice to southern hemisphere observers

Share this post


Link to post
Share on other sites

Another method is using the polar alignment procedure is some mounts.. my CGEM has the ASPA (All Star Polar Alignment) and it's very accurate for a start... get within a few arc minutes... 

Surely the CGEM is not the only mount with such a feature.

 

Share this post


Link to post
Share on other sites

The Skywatcher handsets come with a polar align feature. I haven't used it for a while but I'm sure it uses 2 different stars for adjusting both alt and az axis. Pretty accurate for goto commands.

Share this post


Link to post
Share on other sites

Good point, David. I have Skywatcher mounts now but like you had forgotten about their refinement procedures! I quite like the Skywatcher, but in my opinion no modern mount is anything like as good as the now unobtainable and now almost unrepairable Vixen Skysensor - but that's another topic!

 

Share this post


Link to post
Share on other sites

For visual I found north and level worked ok even on a 2000fl sct...you could drift align if you can see south and east or west..

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Recently Browsing   0 members

    No registered users viewing this page.

  • Similar Content

    • By Eta Carina fan
      Hi. I live in Santiago, Chile, and on a recent trip back home to the US, bought a new Explore Scientific Exos100 PMC mount, to use here for AP with my DSLR and AT72ED scope. I have the ExploreStars app  installed on my iPad, and it links fine, with slewing controls working from the tablet. My problem is, despite the fact that the app displays correctly my southern hemisphere location, the mount tracks as if it were in the northern hemisphere. I cannot find a hemisphere switch on the unit (like found on my SW Star Adventurer). I have written to ES but so far, no response.  I am hoping to connect with EXOS100 users in So Africa, Australia or other southern hemisphere locations, to learn directly from them how they overcame this issue.  Thanks!
    • By antariksha
      Abstract :
      The topic of Polar Alignment is not at all new. Lot of approaches, automation tools are available. Yet, some aspects in all the current approaches drove me towards doing some more work. The key aspects of this approach are as follows.
      Ability to do the Polar alignment without polaris sited Relatively less complexity than drift alignment Ability to address to a good extent the atmospheric refraction to finally locate correct NCP / SCP position A good starting point for amateurs who wish to graduate towards sophisticated tools and techniques Ability to quickly verify if the polar alignment is intact after one object photographed or viewed, and the equipment is being pointed to another object. This point is mentioned in light of the fact that sometimes the polar alignment gets disturbed and the next object photographed shows star trails. This is especially true if payload is tweaked for next photo imaging. What is required?
      One should have a good understanding of the sky and ability to identify stars upto Mag 4.5 using star maps and basic concepts of RA and Dec. One should have Equatorial mount with ability to fine tune Azimuth and Alt adjustments. Availability of cross hair eye piece for the ability to locate the star exactly at the cross hair point. It is good to have finder scope attached and the finder cross hair is aligned with the main telescope eye piece cross hair. Please note this technique is not for the GoTo mounts which many times have Alt-Az mounts fitted with tracking motors. The GoTo alignment is done using 3 Star method.
      However, there are a few mounts which are equatorial design and also have GoTo tracking capabilities with RA and Dec motors. For these mounts, it is preferred to carry out polar alignment. The only point about these mounts, is that GoTo should have ability to start the RA motor ( tracking) without doing the 3 Star alignment, in other words, bypassing the steps for 3 Star alignment.
      The technique is based on the mathematics around the stellar current positions precisely computed. The technique suggests NCP or SCP alignment using specific pointing stars.
      Method
      The technique relies upon pairs of stars identified such that pair has same RA or same Dec. The details about finding such pairs, are given in the next section ( Mathematics).
      Step 1
      Try to do a very coarse polar alignment using your latitude and pointing the equatorial axis approximately towards a possible Polaris direction. This is only to reduce the iterations in the method below. There is no dependency to visually site Polaris. Step 2
      Select the pair of stars of the same RA from the table 1 below. Now, while choosing the pair, please select that pair which is closest to the zenith. This will reduce the error due to atmospheric refraction of siting those stars. Choosing such pair, will get better alignment. Note that the NCP and SCP lie on the same RA contour of the pair, you have just chosen. Locate the first star of the pair in the cross hair eye piece. Loosen the DEC knob of your Eq mount. Let the RA axis not to be loosened. Further, please start the RA motor and hence the tracking. In case of GoTo capability, please ensure the tracking is On, while the 3 Star alignment being bypassed. Rotate the telescope around DEC axis such that the second star of the pair is in the Cross hair eye piece. In the first attempt, the second star almost certainly will not be at the center of cross hair eye piece. And you need corrections. At this point, take the help of the finder with its wider field of view. Identify the position of the second star whether it is below or above the finder cross hair. Adjust the Azimuth of the mount through the coarse or fine depending on how off the second star has been. o   Tip : In case, someone is facing difficulty in finding which direction to move Azimuth of the mount for correction, the following tips may be of use. A simple way to determine is to locate where the second star lies with respect to cross hair. Assume it is on the lower side of cross hair. Then the correction in the Azimuth of the mount should be such that the star is moved upward. It may be noted that your finder can be either inverting or non-inverting. Now, to determine the movement, please hold the finger on the lower side in front of the primary of the finder. And slowly lift the finger towards the center of the primary to obstruct it and continue moving upward. While doing so, please observe from the eyepiece. The blackish ghost image of finger will be seen moving. If movement is lower to upward, the optics is non-inverting. If ghost image moves from up to down, it is inverting. With this small trick, you would know how to apply correction. Once the correction is done, please point the finder to the first and then second star alternately simply by rotating around Dec axis of the mount. Both stars will be seen at the cross hair. At this point, coarse polar alignment is done. Now, please use the main telescope cross hair to locate the first and then second star using Dec axis movement. If required, please carry out the necessary Azimuth correction. Again, please use the above small trick to find out more on how to apply correction. At this point, please note that at the telescope’s high power ( with cross hair eyepiece), the Dec axis is correctly tracing two stars in your pair. Note that NCP/SCP lie on the same Dec axis. The Azimuth alignment of NCP/SCP is achieved. No more touching of azimuth knob of your Equatorial mount now. Step 3
      Site the pair of stars of the same Dec from the table 2 below. Now, while choosing the pair, please identify roughly the midpoint of them. Now, select that pair whose midpoint is relatively closest to the Zenith. With this, one star is relatively East ward and other one almost at a same distance but Westward. This will reduce the error due to atmospheric refraction of siting those stars. Choosing such pair, will get better alignment In case you are unable to select a pair, please read Step 4. Note that the NCP and SCP lie on the centre of the Dec circle which the above pair inscribes. Locate the first star in the cross hair of finder. To locate the second star, please lock Dec axis. But loosen the Eq axis and rotate the telescope around Eq axis. Please carry out Alt adjustments of the mount. Please use similar procedure and tricks as in the step 2. Once the two stars are in the cross hair positions of the telescope, the polar alignment is completed. Step 4 ( only if you could not carry out Step 3)
      Site the pair of stars of the same RA from the table 1 below. Now, while choosing the pair, please select another pair which is off zenith. Please try to select such pair which has both stars approx same elevation from horizon, so that their atmospheric refraction is almost same. Effectively, we cancel the atmospheric refraction influence. Please note that in step 2, NCP/SCP is located to be on one of the RA lines. Now, we use another RA line with this newly selected pair. Again, for these stars to be centred, please keep Eq axis fixed and only move Dec axis ( similar to step 2). However this time, the mount corrections to be done are using Alt adjustments. Once the two stars are in the cross hair positions of the telescope, the polar alignment is completed. Mathematics
       
      The starting point was the star catalog where the Epoch 2000 is taken as baseline. Then I selected the stars brighter than mag 4.5. I applied the corrections due to Earth Precession and also the individual star’s proper motion. With the base data was ready for today's’ star positions. Then I programmatically picked up all pairs for same RA (within 0.001 difference) and later all pairs with same Dec (within 0.001 difference).
      I found mag 4.5 to be heuristically optimal. This magnitude is sufficient for visual locating these stars. Also, the number stars shortlisted from the main catalog is good enough to give sufficient number of required pairs.
      The pairs located today may not be valid after say couple of years due to Earth Precession and stellar proper motion. The below two tables will need fresh computation then.
      Disclaimer: I have tried few of the above mathematically found pairs from my location 19 Lat 73 Log. I use Bresser ExOS 2 mount. After the polar alignment, the tracking was tested for 10 min which was adequate for my current level of astrophotography.
      At different altitudes, different latitudes, this is not tested. I believe, the method will definitely work for small exposures. It is to be validated if this method works for very long exposures.
      Star Pairs
      Table 1 : Star pairs with same RA ( useful for Step 2 and 4)
       
      Sr No
      First star  (name)
      First star HD Id
      Second star ( name)
      Second star HD Id
      1
      Gam Cas
      5394
      37 And
      5448
      2
      Nu Per
      23230
      19 Tau
      23338
      3
      Ups Tau
      28024
      71 Tau
      28052
      4
      90 Tau
      29388
      53 Eri
      29503
      5
      Kap Lep
      33949
      Rho Ori
      33856
      6
      The Aur
      40312
      Del Aur
      40035
      7
      Gam Mon
      43232
      Eta Gem
      42995
      8
      Eps Gem
      48329
      30 Gem
      48433
      9
      13 CMa
      50013
      V0415 Car
      50337
      10
      Omi CMa
      50877
      The CMa
      50778
      11
      P Pup
      63922
      Xi Pup
      63700
      12
      Chi Car
      65575
      11 Pup
      65228
      13
      Del Hyd
      73262
      E Vel
      73634
      14
      B Vel
      74180
      V343 Car
      74375
      15
      Iot Cnc
      74739
      Eps Hyd
      74874
      16
      31 Leo
      87837
      Alp Sex
      87887
      17
      Pi Cen
      98718
      Sig Leo
      98664
      18
      Lam Mus
      102249
      Nu Vir
      102212
      19
      Alp Crv
      105452
      Del Cen
      105435
      20
      Gam Cen
      110304
      Gam Vir
      110380
      21
      5 Boo
      120477
      2 Cen
      120323
      22
      SHT 56
      129116
      Alp Lup
      129056
      23
      Del Her
      156164
      Pi Her
      156283
      24
      102 Her
      166182
      Pi Pav
      165040
      25
      110 Her
      173667
      Phi Sgr
      173300
      26
      Zet Cap
      204075
      Gam Pav
      203608
      27
      Del Gru
      213009
      Del Cep
      213306
      28
      Iot Cep
      216228
      Mu Peg
      216131
      29
      Bet Peg
      217906
      Bet Psc
      217891
       
      Table 2 : Star pairs with same Dec ( useful for Step 3)
       
      Sr No
      First star  (name)
      First star HD
      Second star ( name)
      Second star HD
      1
      7 Cam
      31278
      Gam UMaj
      103287
      2
      Iot Cyg
      184006
      The Boo
      126660
      3
      H Persi
      26630
      Dmi?? Cass
      4180
      4
      Pi Aur
      40239
      Iot Her
      160762
      5
      39 Cyg
      194317
      Omi Persi
      23180
      6
      Eta Peg
      215182
      Zet Cyg
      202109
      7
      Iot Cnc
      74739
      Bet Tau
      35497
      8
      Bet Peg
      217906
      Vet Cyg
      183912
      9
      54 Leo
      94601
      Alp Vul
      183439
      10
      Alp Tau
      29139
      Gam Gem
      47105
      11
      Mu Ceti
      17094
      Lam Ori
      36861
      12
      Omi Psc
      10761
      Bet Cnc
      69267
      13
      Pi Ori
      30836
      Del Hyd
      73262
      14
      3 Agr
      198026
      Lam Agr
      177756
      15
      Iot Ori
      37043
      Iot Vir
      124850
      16
      Lam Eri
      33328
      Eta Eri
      18322
      17
      The Lib
      142198
      Del Crv
      108767
      18
      Bet Cet
      4128
      Bet CMaj
      44743
      19
      88 Aqr
      218594
      Pi Sgr
      178524
      20
      88 Aqr
      218594
      Xi Oph
      156897
      21
      4 Xi CMaj
      46328
      3 Eri???
      18978
      22
      Rho Pup
      67523
      Omi CMaj
      50877
      23
      Omc Cau???
      56139
       
      61555
      24
      Bet Hyd
      103192
      43 Eri
      28028
      25
      2 Cen
      120323
      Eps Sgr
      169022
      26
      Alp CrA
      178253
      Mu Seo
      151890
      27
      Bet CrA
      178345
      Lam Gru
      209688
      28
      Phi Cen
      121743
      Eta Cen
      127972
      29
      Eta Col
      40808
       
      73634
      30
      Vel
      78647
      Gam Phe
      9053
       
      Good luck
      Ashirwad Tillu ( ashirwadtillu@gmail.com), user name ( antariksha)
    • By Kcks Regulus Star
      On the 2nd of July I closed my curtains one night before I went to bed but, before they were shut I noticed a strange multicoloured light flickering low in the sky in the northern celestial hemisphere. I Thought to myself if that is a star it looks amazing. The next night (3rd of July) I decided to take another look at this multicoloured light which was still there, Only this time I used my binoculars, I was seeing blues, greens & reds. We have all seen stars by looking up into the sky but, I have never seen a star create multi colours before. It makes you feel excited inside and you think that no one else can see this until you tell them and share the same experience together. I believe I was looking at the Capella Star which is the brightest star in the constellation Auriga and your not kidding it is bright. I cant wait to have another look tonight to see if the multi colours are still there. I would like to have taken at picture of it but I am not setup to do that just yet as I am very new to star gazing. I wish someone here can confirm what I saw and to post a picture of it would be awesome. 
      Nikon Prostaff 3s 8 x 42
    • By borapanda
      Hi everyone!
      I have a Celestron Astromaster 114 eq (114/1000mm), and I do use it whenever I can, but I'm still quite the newbie when it comes to observing.
      My point is, I'd like to observe the planets, but  I dont't think the standard eyepieces that came with my telescope (10 mm and 20 mm) are powerful enough for that. For reference, the "furthest" I could see were the rings of Saturn , but they were very small and faint too.  
      Are there any specific eyepieces you could recommend? :) And of course, any tipps and advice are also very much appreciated.
      Thanks, Sophie.
    • By Fraunhoffer
      lets imagine I wasn't to see a nice DSO about 15' size and I think it should look good nicely framed with a 1 deg field of view in the EP..
      Which would give the better (or higher probability of seeing anything at all ) view from a semi urban light polluted home site (e.g Bortle 6)?
      a) an 100mm f/6 refractor (fl 600mm) and a 10mm EP (60 deg afov, gain 60x = fov pf 1 deg)
      (and exit pupil of 100mm / 60 = 1.6mm)
      or
      b) a  200mm SCT with focal reducer to give f/6 (fl 1200mm) and a 20mm EP (60 deg afov, gain 60x = fov of 1 deg)
      (and exit pupil of 200 / 60 = 3.3mm)
      My gut feeling is that the SCT should give a better view just based upon its 2xaperture - but Im not sure I understand fully the maths why.
      Is the larger exit pupil going to result in a better / brighter / more successful view?
      Or will the view be 'roughly' the same ?
      Or have I got it all wrong.....

      Thanks.
×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.