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Messier 81

That’s M81, first time I found it in this light polluted town. Also the first time I polar aligned my Celestron NexStar 5SE. I highly recommend polar aligning your scope, especially when you’re gonna do astrophotography. Why? Because a polar aligned telescope only rotates on one axis with a single motor (which means: more precision) and the photos don’t rotate from one frame to the other. But because the alignment procedure is quite involved and not well documented in the manual (or on the internet for that matter), here’s what to do if you too live on the Northern hemisphere. PS: This is the absolute minimum. We’ll cover an additional wedge align in another post.

1) The NexStar 5SE has a wedge. This wedge must be lifted such that it’s adjusted for your latitude. In my case, I live at latitude 52º, so I align the base plate to the 52º mark. You can do this during day time:

Wedge latitude align

2) Setup your telescope outside to let it adjust to the temperature and power on the NexStar computer and the GPS. Set it up in this initial position, pointing to Polaris. You can move the tripod around such that Polaris is more or less centered. It is important that you point your telescope to Polaris as good as you can.

Initial position

3) Wait until the GPS is linked:

GPS linked

4) When the GPS is linked, choose EQ North Align:

Polar alignment - EQ North Align

5) The first thing the NexStar asks you to do is “Set Alt to Index”. You need some light (e.g. from a red lantern) for this, and it means that you use the up/down controls of your NexStar hand control to align the two arrows:

IMG_0907

When you have done this, the telescope is pointing towards the ground! This is exactly as it should be!

6) The NexStar now asks you to “Find the Meridian”. This is the tricky bit:

Find meridian

You now have to slew the telescope with the hand control’s right arrow button so that it points towards the sky AND is aligned to the meridian. In the sky, the meridian is the imaginary great circle on the celestial sphere. It passes through the north point on the horizon, through the celestial pole, up to the zenith, through the south point on the horizon, and through the nadir, and is perpendicular to the local horizon. This means you have to swing the telescope clockwise for a half turn (180° or π rad if you like math) until it points to the sky again, away from Polaris. It helps me to put my iPhone with a compass app on top of the telescope until it is aligned North to South:

Polar alignment - iPhone compass to find meridian

Your telescope now points to the sky, away from Polaris!

7) Now choose “EQ Auto Align” and align the telescope as you normally would do to two of the suggested stars:

Polar alignment - EQ AutoAlign

8) Voila! Your NexStar is now polar aligned. For more accuracy, you can still use “Precise GOTO“. In fact, that’s how I found the above Messier 81. My first trial with the regular Messier menu found nothing. But “Precise GOTO” yielded a much better result; M81, dead center!

Of course I would like to improve on this result. I think I can aim a little higher on the following, considering the equipment stays the same:

  • Find a place with less light pollution.
  • Take more pictures.
  • Also do a wedge align and generally make sure M81 stays better centered on the ccd.
  • Spend more time focusing.
  • Experiment with exposure settings. At 10″, M81 seems to “blow out” at the center. So less may be more here.

Stay tuned for another photo of M81.

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