Calculate position of pole star

[cowasaki]

Watching dion's video about polar alignment he shows a piece of software called polarfinder which shows a circle and on that circle the location of the pole star.

Without using this software does anyone know how to calculate the location angle to find the position around the circle?

[Ags]

Er... Look on stellarium?

[JamesF]

Don't bother. Really.

Polaris is highest above the northern celestial pole at midnight on 1st November, so the easiest way to get the reticule correctly orientated (which is why I assume you want to know where Polaris should be) is to rotate the mount about the RA axis until the marker for Polaris is at the bottom of the polar scope reticule (because it's upside down compared with the sky), then rotate the time and date rings for midnight on November 1st and adjust the index ring so it's in the right place.

There's more information here:

http://stargazerslounge.com/beginners-help-advice/103827-polaris-transit.html#post1432597

James

[RichardL]

Some while ago I created the attached table and graph to sort out my own setup. I have a pole-finder tube that sits on top of the mount. The far end of the tube is a little larger than the circle that Polaris makes round the pole. The aim is to get Polaris in the correct clock-face position as per the table. You also need to know the local sidereal time; you can download a sidereal clock from

Download a Sidereal Clock for Your Desktop

position_of_polaris.pdf

[skywatcher58gb]

Hi Cowasaki

Go online and type in 'Kochabs clock' and you will discover this method for polar alignment.

dave

[cowasaki]

Some while ago I created the attached table and graph to sort out my own setup. I have a pole-finder tube that sits on top of the mount. The far end of the tube is a little larger than the circle that Polaris makes round the pole. The aim is to get Polaris in the correct clock-face position as per the table. You also need to know the local sidereal time; you can download a sidereal clock from

Download a Sidereal Clock for Your Desktop

Thanks, this has helped together with this page on how to calculate the sidereal time....

Sidereal time formulas and spreadsheet to navigation accuracy

[cowasaki]

The reason I wanted to get the information is because I am building a astro computer from one of the more powerful Arduinos and a graphical display. Full control of a camera etc (already, because I had already designed and built a camera control computer), dew heaters, GPS, voltage regulation for syn guider etc etc etc. As the device contains an RTC I thought I would re-create the graphical display for the pole start locator actually on the device

[cowasaki]

Thanks everyone, especially Richard.

Just put it all on a quick spreadsheet till I have the calculations right and can test it but this is what I have so far. It does not take into account Long/Lat and local sidereal time yet but I'll post one later that does. Once this is working I can add it as a little bonus to the astronomy computer device so a quick selection of that menu option can bring up the pole star diagram for alignment.

Sidereal calculator.xlsx

[themos]

Do you need to correct for precession/nutation etc? I was surprised to find out that the NCP has moved more than 4 arcminutes since 2000.

[cowasaki]

Do you need to correct for precession/nutation etc? I was surprised to find out that the NCP has moved more than 4 arcminutes since 2000.

There are more accurate algorithms that I have found which I might switch to IF I decide to display the sidereal time as an actual time. At the moment it is just being used as the input to the formula that gives the output as per Richards graph. That figure is then converted to degrees and will be displayed on a circle about 4-5cm across which means that an inaccuracy so small would not be detectable. I do have the information to make it accurate to within a couple of seconds right up to at least 2050 but it just makes it more complicated than it really needs to be for now.