Calculating Polaris transit

[iamjulian]

Hello

I am a bit stuck with my polar aligning. I am almost there with much help from Astro Baby's brilliant article. However, after downloading the Polaris Finder software, I don't get how to find the date and time at which Polaris is at it's highest point. Using the software I can see where it is in relation to the north celetial pole at any given time of the day - but how do I work out which day of the year it is highest?

In Astro Baby's guide, as an example, she uses a transit time of 23:00 on October 10th. How do I find that information? I must be missing something obvious.

Any help greatly appreciated!

Julian

[BlueAstra]

Try this web site:

http://www.usno.navy.mil/USNO/astronomical-applications/data-services/mrst-world

You can use it to display the rise/transit/set times of many celestial bodies including the moon, planets, stars, etc.

[iamjulian]

Thank you. It shows the daily transit time, just like the Polaris Finder software does. So am I trying to over complicate things by trying to find out the date of the year in which it reaches it's highest transit?

In order to set the mount's date circle, will tomorrow at 14:20, or the day after at 14:16, etc, give me an accurate enough result? If not, how do I find out which day of which year to use?

[Astro_Baby]

Hi,

What I do is set POlarfinder to display 4 sets of graphs. Then I tweak the time difference between the pictures to locate when Polaris will transit.

ie if I have 4 pictures from Polar finder ranging between (just for demo puproses) 22:00 and 23:00 and the firts one shows POlarius not at transit and the last one shows it after ransit. I just change the time values (ie set the increments between the graphs) so that they are 10 minutes apart. If thats too much I set 15 minutes aprt and so on until I have one picture at transit. Whatever date and time thats given at is where its at.

Extra advice here ( I have yet to rewrite the guide to take in all the questions I get asked). You need to set the date time circles about once a month for accuracy, ideally they are set for each observing session but thats too much of a pain.

I have found though that so long as you do the job accurately firts time the settings will be plenty good enough for a year at a stretch.

If you have GoTo on your mojnth the latest versions of Synscan give you the Polaris position as a clock position - i find that useful as a sanity check.

[iamjulian]

Thanks Astro Baby, so I was making it too complicated. In that case the web page suggested by BlueAstra is the way to go.

Thank you both.

[RikM]

Just read through this thread and had one of those Eureka moments, then had to kick myself for being so stupid...Polaris transits EVERY day, so you only need to know the transit time for the actual day you actually set the circles.

Hahaha.

Just have to wait for my polarscope to arrive from FLO now.

Rik

[davidcox257]

Hi Guys,

I have a question concerning the accracy of polar transit data from the various sources quoted in this and other posts. Let me give an example for todays polar transit times (16th December 2012).

The USNO Navy web-site (earlier post in this thread) shows a Polaris transit time of 21:09

SkySafari shows 21:07

REd Shift shows 21:08

SkyMap Pro shows 21:08

Polar Finder shows 20:52

The big descrepancy appears to be with Polar Finder which a lot of people use....

I've ensured that all my data is correct (Latitude, Longitude, Time, time zone etc)....

So why are they different and which one is correct?

Anyone have any ideas, please?

[Astro_Baby]

My bet would be that most of these pavkagaes use some form of calculation which may not take into acouny all possible daye, this is why there are still observatories providing observed data. No idea what value may be needed, precession, nutation, proper motion etc etc.... But the earth doesnt orbit in precise time and it has a natural wobble plus its rotational speed slows down etc etc all of these factors may throw the calculations for a polar transit out is my guess.

The naval observatory will probably be accurate because traditionally they are based on the most up to date observational data.

Thats jus a guess by the way.

[Balrog Nebula]

I am a beginner in the field of stargazing but I can already say that Astro Baby saved me from lots of frustration with her "Polar Aligning the SkyWatcher HEQ5/Orion Sirius Mount" article. I found that her tutorial also works with my NEQ3.

Thanks also to BlueAstra with his/her reference to the Naval Oceanography Portal (USNO).

Enough praised, here are my questions:

1-     In her above mentioned article, Astro Baby indicates that people living in a different time zone may need to adjust for Longitude Offset. I am living in longitude 73 west, 2 degrees east of my central meridian 75 west. I am OK up to that point but for the rest of the required steps, Astro Baby doesn’t provide baby-step-by-baby-step information “with pictures” in order to finalized the zeroing of the Longitude scale… and I am not sure what to do next...

2-     On another topic, I was playing with the declination circle of my scope and found out that this circle can rotate freely once the little screw is slacken… and then I found out that I shouldn’t have played around with that circle because it had been calibrated by the manufacturer… So, my declination circle is now decalibrated. Is there an easier way to re-calibrate it other than setting it to the known declination of a star once my scope has been polar aligned?

Thanks in advance for your responses…