Thursday, April 04, 2013

tested 3-star alignment (Toronto)

The weather predictions were not looking great so I thought it might be a good night to work with the GoToStar system. I got distracted last night; tonight I'd test it. Learn more.

In particular, I wanted to understand the 3-star alignment process. I wanted to see if I could "reduce" the numbers in the RA "error" report. And with low numbers I wanted to see how accurate the goto function was. All, without doing a proper visual polar alignment... I installed the baader 36mm eyepiece.

8:24 PM. After checking the location, time zone, date, time, I then performed my first 3-star alignment. I selected three stars from the menu and noted the RA axis report values.
  • stars: Aldebaran, Betelgeuse, Regulus
  • altitude: 129.4' lower
  • azimuth: 94' east
I saw high thin cloud.

Based on remarks in messages in the Yahoo!Group, I decided to raise the mount and and turn it slightly west. I.e. correcting opposite to what the report showed.

I noticed, to get to each star in the finder scope, I had pressed the right and down keys. Interesting.

8:32. Round 2.
  • stars: Aldebaran, Betelgeuse, Regulus
  • altitude: 49.6 lower
  • azimuth: 66.8 west
An objective for these trials was to be as consistent as possible. Unfortunately, I wasn't able to see Regulus for tree branches, so I had to guess. Still, the numbers seemed to be improving.

8:39. Regulus was still in a thicket, so I opted for a new third star.
  • stars: Aldebaran, Betelgeuse, Mizar
  • altitude: 52.3 lower
  • azimuth: 130.9 east
Hmm. Not better. But then, I had upset the applecart.

8:46. Noticed the position for the RA axis was off a bit, after returning to "home," so I reset it. Dec was on the button, on 90°.
  • stars: Aldebaran, Betelgeuse, Mizar
  • altitude: 20.7 lower
  • azimuth: 150.1 east
Again, I had to guess a bit. I saw α (alpha) Orionis in the finder but not in the 'scope! And it looked like I was going the wrong way in azi.

8:55. Checked the weather conditions on the OneWorld pocket weather station, sitting atop the 'cue: 1006 millibars pressure, 20% humidity, and 7°C. It felt colder!

8:57. Another round...
  • stars: Aldebaran, Betelgeuse, Mizar
  • altitude: 3.0 higher
  • azimuth: 91.6 east
Ah ha! I was nearly perfect on height; and going the right direction, again, for the azimuth.

9:04. Reset the RA axis to zero again. Turned more west again, and dropped the height this time.
  • stars: Aldebaran, Betelgeuse, Mizar
  • altitude: 8.5 higher
  • azimuth: 32.2 east
Oops. Something went wrong with the elevation. Still improving on azi.

9:09. Again!
  • stars: Aldebaran, Betelgeuse, Mizar
  • altitude: 7.0 lower
  • azimuth: 13.6 west
OK. Pretty good. I decided that was enough fiddling. I wanted to evaluate the goto performance.

9:12. From the computer, John Littlejohn, in the kitchen, I told SkyTools 3 Pro to connect to the mount. Didn't seem to work. I returned to the mount and saw the RA report. Oops. I had forgotten to clear the message. As soon as I did, the slew commenced. Back at the netbook, I discovered a time out error on ST3P.

9:14. I had slewed to Jupiter. I saw it at edge of eyepiece. I centred on the planet and did a sync command at the hand paddle. I thought I heard Audrey comment in Skytools...

9:20. Slewed to M42. It too was at the edge of field. I centred again, synced again. Listened carefully. Nothing on Skytools. It must have been my imagination.

Tried to slew to M36. I think it missed. There was nothing obvious in the field nor at the edge. Panning around I stumbled across a cluster. But then doubted it was 36.

9:23. Chose Castor. It was off. I wondered if the sync command had made it worse. It was in the finder. I checked ST3P. The X pointer (for where it thought the 'scope was pointing) was off in software. I decided to try corrected in the software as opposed to at the hand controller.

I right-clicked on Castor in Context Viewer chart. Chose "sync telescope to cursor." As expected, I saw the error dialog box, not responded correctly. I reconnected to the mount. Checked the chart. And it looked OK.

9:28. Went back to M36. It was at edge of field. Huh. It looked like ST3P had fixed it!

9:32. Slewed to ζ (zeta) Cnc. Nope. It was off again. I saw a bright star in the finder, about a degree or so away.

The skies were fair. I decided to try for something "real." 

9:39. Tried for 26 Aur. I saw a pair in the low power ocular but I didn't see any colours. White and maybe orange? Possibly? Widely separated. They were maybe 1 mag different in brightness. Haas describes as "lemon white and azure white."

9:47. Nope. Incorrect. I was on the wrong double star. That's what you get for "trusting" a goto mount. I was on HR 1945. Gah. I had to go north-west.

Arrived 26 Aur, finally. Viewed at low power. Yes. It was colourful. The primary was a yellow gold or orange star with a fainter blue companion. This was a suggestion from the RASC Coloured Doubles list: yellow, blue, and faint. Yep. Haas describes the pair as straw-yellow and Atlantic blue.

Noted that SkyTools showed I was viewing the AC pair. The AB is very tight, not possible visually. There was also a D star but I wasn't interested...

OK. While there was not any major clouds happening, it just didn't seem very good. I decided to wrap up.

10:00. Shut down the mount and started packing up... Earlier in the evening, I had already torn down the light blinds.

Oh, Fizzbin. I did it again! I shut down 'scope first. SkyTools does not like that. The ASCOM driver goes into an infinite loop and then ST3P self-destructs.

It was 1005 mb, 20%, and now 5.7°.

10:02. Done.

So, overall, not entirely impressed with the 3-star alignment feature. It did not seem to produce highly accurate goto results. To be fair, I do have significant concerns about the mount itself. I think there's slop in the bearings, slop in the gears. The deck could be moving underfoot. So, perhaps, I should not be too harsh. Now, that said, it was a lot of back-n-forth to improve the axis error; when the 1-star alignment seems to hit targets fairly well, with a lot less effort. Makes one wonder.

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