Earth Precession - New Photo Technique Showing A Vega “Polar” Startrail
Taken by Miguel Claro on April 19, 2015 @ Alqueva Dark Sky Reserve, Portugal
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Date Taken: 2015:05:04 23:31:57
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I would like to contribute in your publication with my newest work and technique to show the Earth Precession.

Since the very first moment I read and learned about the Precession of Earth that I was fascinated with the possibility of having a different star than Polaris, pointing to north, although in that time, few years ago, I didnt had the right technology and even the chance to could show in a real image how it would would be the sky of my land if I had another star in the place of the well known, Polaris ?

After a long time of burning my mind with some new ideias, I figured out how I could do it, developing what I think is, a totally new astrophotographic technique never applied before, and where I can show in real time the sky rotating around another star, simulating the shifting of Earth Axis even being inside our Earth.

In astronomy, axial precession is a gravity-induced, slow, and continuous change in the orientation of an astronomical bodys rotational axis. In particular, it refers to the gradual shift in the orientation of Earths axis of rotation, which, similar to a wobbling top, traces out a pair of cones joined at their apices in a cycle of approximately 26,000 years.

A consequence of the precession is a changing pole star. Currently, Polaris is extremely well suited to mark the position, as Polaris is a moderately bright star located about 0,7º degrees from the pole. But with the crescent light pollution is Increasingly difficult to distinguish the few bright stars in the middle of cities, so near the year 14 000, the brilliant Vega in the constellation Lyra, is touted as the best north star. Although, it never comes closer than 5° to the celestial pole.

When Polaris becomes the north star again around 27,800, due to its proper motion it then will be farther away from the pole than it is now, while in 23,600 BC it came closer to the pole.

What I did to create the both startrails and time lapse images, was to use 2 mountings Vixen Polarie, one to pointing to the actual Polaris Axis and making all the stars staying fixed, but using another Polarie attached to the first one, I could simulate again the Earth Axis Rotation using the sideral motion inverted (I mean, like if I was in the south pole, near the batteries you can switch the button to (N) north or (S) south motion).

But I had special carefully with some things. I have waited until Vega star reach the same altitude I had in my observing latitude, in my case 38º, to have the same distance to the horizon that I have when looking to Polaris.

I had to align carefully the star Vega near the center of the image, to create the axis rotation simulating the 5º separation of the celestial north in +14000 (year). I also used the Live View magnifier with the grid option to have a more precise result.

As this technique induces movement, the landscape will move a bit from the first frame to the last one, but in the final startrail still image, I made a mask merging the landscape with the first frame again to have a more pleasant result.

All the images were taken from inside the Mourão Castle, in the Dark Sky Alqueva Reserve, the First Starlight Tourism Destination in the world, in Alentejo, Portugal.

Startrail images about Precession:

Vídeo Time Lapse about Precession:

Images of the equipment used and described:

Technical info :
Polaris Startrail starts in 19/04/2015 at 23h48 and Vega startrail starts in 20/04/2015 at 1:07

Canon EOS 6D - Canon EF 8-15 f/ 4L Fishseye USM at 8mm (All Sky). Exp. 30 sec. ISO 2500
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In year 14000, Vega will come at the position where currently Polaris occupies.
By the axial precession, the direction of Earths rotation axis (i.e. Celestial north and south) will change from Polaris to Vega, however, not only Earths rotation axis but also the whole Earth itself will turn around.
Since the positions where the axis crosses the surface of Earth will not change, the direction to the north from the observation place on the Earth will not change by precession, I think.
In these photos, the observation place and the field of view seem to be the same.
So, I think that the direction to the north on these photos will not change and that the overall view of startrail circles will not change between year +2000 and +14000. Only the star near the center of startrail will change from Polaris to Vega by the shift on the celestial sphere.
Posted by shiram 2015-05-05 01:00:17
Shiram thats exactly right. North on Earth will still be in the same place. The change takes place in the sky only. From currently 90 deg declination, the NCP will move south (duh), making part of the current southern sky accessible to Northern observers and vice versa. Still a nice effort by Miguel.
Posted by berndb 2015-05-06 19:42:41
Thank you, Bernhard. I discussed on this point with Miguel, and he knew that, but his explanation is that it is important to include the same landscape in the current startrail in his project and that the shift of startrail center is currently inevitable because now is still 21st century, in my understanding. Of course, his project of future startrail with landscape is very interesting, so still a nice effor by Miguel, I think, too!
Posted by shiram 2015-05-07 09:11:20
Hm, as it was pointed out by others, it is not correct. The celestial pole will be at the same position _with_respect_to_the_landscape_

Lunisolar precession does not alter the observers geographic latitude.
Posted by gabor.timar 2015-05-07 12:44:27
Great work, regardless of some of the comments...
Great shots, I just love star trails AND
Congrats on making it to both the Spaceweather front page and APOD for 8 May!!
Posted by HP1954 2015-05-07 23:46:23
62 thumbs up
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