# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: Sundog
Date: 2013 Feb 16, 13:07 -0500

Hi Greg

Frank has not provided either mean or apparent time.  This will limit our precision, as will the altitude estimate!

As a bracket, the azimuth is 110 deg 20 min for 5:00PM and 113 deg 42 min for 4:40 PM. (I used 112 deg 0 min for 4:50 PM).  It appears that we can be off by as much as 1 deg 42 min for a 10 minute shift in time.

Could we use our sextant as a sundial to tell the apparent time, given the observed altitude?

On Feb 16, 2013 12:54 PM, "Greg Rudzinski" <gregrudzinski@yahoo.com> wrote:

After closer inspection of the image it looks as if the actual sundog Hs is between 2 and 3 degrees. Measure the distance between the two bright spots in mm. 22/ measured mm = degrees per mm. Now measure sundog mm above horizon to get Hs. Use an online sight reduction calculator to get the desired Hs and azimuth at 41 north latitude on the given date . I'm getting about 248.8* +22* = 270.8* azimuth

Is there a UT time for the image ?

Greg Rudzinski

[NavList] Re: [NavList 22379] Re: Sundog
Date: 16 Feb 2013 12:00
Hi Greg

Frank mentioned it was about sunset. The sun sets about 5:19 PM mean time, Latitude N41 on 10 Feb. Unfortunately, there is no meta-data associated with the image so we cannot tell the precise time. Frank has made specific statements about 10 Feb, stating that on this day, "it is noon at noon". Therefore apparent time aligns with mean time.

"Azimuths of the Sun" 1934, gives a table for N41 latitude, declination of opposite name. The table clearly states that the sun sets at 5:10PM apparent time, at azimuth 108 deg 42 min. Enter the table with declination (S14) and apparent time of sunset, less 20 minutes. Why 20 minutes? For the 5 degrees of altitude. The table entry for 4:50PM, Dec 14 gives 112 degrees 0 minutes.

Since this is reckoned from N to W, the sun's true azimuth is 360-112=248 Degrees. Add the sun dog offset of 22 degrees and we are facing 270 degrees.

For a closer estimate, the mean time of the picture and the true observed altitude ( was it truly 5 deg?) would have been helpful.

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