The Precession of Earth – New Photo Technique showing a Vega Polar Startrail.
All Sky View | Alqueva´s Dark Sky Reserve | Best Of | By Year: 2015 | Identifying the sky above - Science & Education | Monuments Heritage & History | Polar Trails | Stars and Constellations | Startrails | Time Lapses Photography
Featured as NASA´s Astronomy Picture of the Day (APOD).
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 didn’t had the right technology and even the chance to could show in a real image how it would be…how 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 body’s rotational axis. In particular, it refers to the gradual shift in the orientation of Earth’s 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.
Very Important: The second condition to give the right movement, was to align carefully the star Vega near the center of the image (my new Earth Axis – now a Vixen Polarie Axis), 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.
*Important Note: Precession changes the direction of the Earth axis from Polaris to Vega on the celestial sphere, but the positions where the axis crosses the surface of Earth will not change by precession. So the north on the Earth from the observation point will not change, and the latitude of the observation point will not change too. Although, I choose the option that includes “apparently” almost the same landscape field view and where fits both Polaris (at left) and Vega (center), because if I had putting the Polaris in the same central framing position, as I did with Vega ( remembering that is the only possible way – as a condition – to simulating the Earth Axis rotation using the Vixen Polarie sideral motion, and show nowadays, the motion of the stars around Vega in a real Time Lapse movie sequence), I would loose the same landscape field of view with the Castle Tower, and this was also important to give people the notion that the image was really made in the same place. Vega is about 51º away from Polaris, so it means a big change in the field of view towards another position in the sky and consequently, in the landscape, in this case towards left, to Azimuth 0º – North, where stand the Polaris star.
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.
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
