Latitude dependence on the horizon in a "star wheel"

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  • Member since
    March, 2002
  • From: 59d24.3'N17d49.1'E
Latitude dependence on the horizon in a "star wheel"
Posted by boberglund on Sunday, December 29, 2013 2:05 PM

I read Glenn Chaple's January 2014 installment of Observing Basics named "Astro-freebies" and got interested in the do-it-yourself star wheel discussed in one paragraph (Uncle Al's Star Wheel).

So I went over to the star-wheel website via the pbs website in the article.

Now I have a question regarding the design of the wheel:

There is an oval hole in the wheel holder, which shows the current sky depending on date and time.
But surely this horizon must depend also on the latitude of the user?
I suspect that the creator (Uncle Al) has used some median latitude of the USA, which will be some 40 deg N lat.

But since I live at 60 deg N lat I probably have to move the cut-out oval in some direction to make the stardome more correct. But in what direction and by how much?

I would like to know how to modify the pattern of the holder such that my grandsons could create a star wheel that works in our latitude.

Any insights welcome! Smile

Bo B
Sweden
(N59d24.27' E17d49.12')

  • Member since
    November, 2009
Posted by Poppa Chris on Sunday, December 29, 2013 2:33 PM

Right you are on the horizon question.  At 60` N Polaris (your wheel pivot point) will be 60` above your northern horizon.  Subtract 60` from 180` (120`) to get the offset to your southern horizon.  Further, your zenith will be at 90` from your northern horizon, or an additional 30` beyond Polaris.  I hope this helps.

---Poppa Chris---

Denham Springs, Louisiana USA

"Second star to the right - Then straight on until morning!" - Peter Pan

Celestron CPC1100GPS (XLT) - 279mm aperature, 2800mm Focal length. (f10) Celestron Ultima LX (70deg AFOV) Eyepieces 32mm thru 5mm, Canon EOS Rebel T2i DSLR, Backyard EOS imaging software, Orion Star Shoot Planetary Imager IV, Celestron Skymaster 15x70 binoculars

 

  • Member since
    March, 2002
  • From: 59d24.3'N17d49.1'E
Posted by boberglund on Sunday, December 29, 2013 3:55 PM

Hi Poppa,

I have used one of the star maps (the one with a grid) and put behind the holder in the correct position. I also marked the center of the elliptical sky hole in the holder.

Then I found that the center falls on top of the 50 degree circle.

This really indicates that the wheel was made by someone farther north (maybe Al lives up at the Canadian border?). Not at 40 deg but at 50 deg N.

I guess I should center my viewport at a star map latitude of 60 deg to make the map look closer to what we actually see?

 

Bo B
Sweden
(N59d24.27' E17d49.12')

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