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Tilt of Earth's Axis and Surveying

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dave-lindell
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@nate-the-surveyor   Just play anything by Vivaldi; they all sound the same.


 
Posted : April 18, 2020 3:34 pm
nate-the-surveyor
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Bbbbut, if you take out the 4 season's, it looses its relationship to the tilt of the earth...


 
Posted : April 18, 2020 5:13 pm
larry-scott
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The tilt of earthƒ??s axis to the orbital plane has only very small impacts to high order astronomical surveying.

The declination of stars changes slightly on an annual basis. When using star observation for azimuth, star ephemerides are always used.

The declination of Polaris, does change. From 01-Jan-2020 to 31-Dec, the declination of Polaris increased 16.3 seconds. Which is used in the calculation of the azimuth of Polaris at the UT of observation. Current Declination of Polaris is 89-20-56. Which returns an azimuth of 359-20-56, or 0-39-04 at elongation. The right ascension of Polaris changed 75 seconds over the course of the year. Not due to axial tilt ?ÿ

In contrast, The declination of Sirius increased 3.3 seconds over the entire year. And its right ascension changed 3 seconds for the year.

The precession of earthƒ??s axis is very little per century. The tilt changed by 0.04 seconds in the last 30 days. Nearly static.

When observing the sun for azimuth, the sunƒ??s declination changes rapidly, 60 seconds per hour, at equinox. And that is near zero on solstice. Which has nothing to with tilt, thatƒ??s due to earthƒ??s orbit around the sun.

These days, astronomic observation for azimuth is arcane. Interpreting Historical records of surveys takes a bit of research.?ÿ


 
Posted : April 19, 2020 6:57 pm
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