APOD: When Vega is North (2015 May 08)

[Jarod997]

Thank you Chris - that's what I thought. The earth still spins on it's axis, is just where that axis is pointing in space that changes over time. It's like taking a photo of a speeding car with 1/4 second exposure time and being asked to identify the make and model - sort of. (The car is... yellow. )

I can see how this composite can be misleading, but I still think it was cleaver of the photographer to make the spiral around a different star from Polaris.

[CarlB]

[...] The only things that will affect where the rotation point is in the picture are polar motion and continental drift.

Of course it's continental drift! The image is exactly correct; in 14,000 years, the building's location will have shifted in latitude to produce that exact image.

Oh, and the building and foliage will be religiously recreated by people of that time to exactly match the original image.

[Boomer12k]

What was the prvious North Star... And when, if ever, will Polaris be the North Star again?

Interesting pic.... But you could use an astronomy program and advance the Precession setting, but not as fun, right?

:---(===) *

[Chris Peterson]

What was the prvious North Star... And when, if ever, will Polaris be the North Star again?

Polaris will be back around in 27800 CE. Of course, it exhibits a degree of proper motion, so over time it will drift away from the pole even without considering precession.

Various stars in Ursa Minor have been marginal pole stars in historical times. Alpha Draco was a good pole star around 3000 BCE, although not as bright as Polaris.

[Dizzynow]

It's dangerous because it makes a person dizzy to look at them .. and if a person is driving a car while looking at them it's Very dangerous. APOD should be banned from the internet for posting such dangerous stuff.

[ta152h0]

and the South pole is void of a star ?

[Chris Peterson]

and the South pole is void of a star ?

For the moment, yes. At least, one bright enough to be useful.

[alter-ego]

What this displays is axial precession, which on Earth occurs on a 26,000 year cycle. Does this mean that the 23.4 degree tilt of earth axis changes as the planet wobbles? I believe this is in relation to the ecliptic, but the wobble would apply in relation to any fixed point. Would this also not have a dramatic effect on the Earth's seasons?

Our axial tilt varies only a little, from about 22° to 24°. That does have an impact on long term climate, which shows up cyclically since the variation in tilt is partly related to our precession (modified by motion of the ecliptic itself due to planetary perturbations). The Moon also causes a bit of variation in tilt, although it actually is responsible for stabilizing it (Mars, which has no moon, experiences very wide variations in axial tilt).

The variation wrt the ecliptic is about as you say. Over a longer time scale (1 million years) the ecliptic pole declination (J2000) is predicted to vary from 64° to ~69.5°. The combined wobbles of the ecliptic and the Earth's obliquity complicates how our NCP position evolves, even over a couple precession periods. (Plots below are from a previous post: http://asterisk.apod.com/viewtopic.php?f=30&t=34333)

 
 
 

[size=125][color=#BF0000]1Myr Precession wrt the Invariable Plane - T is in centuries from J2000[/color][/size]

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[shiram]

Thank you Chris - that's what I thought. The earth still spins on it's axis, is just where that axis is pointing in space that changes over time. It's like taking a photo of a speeding car with 1/4 second exposure time and being asked to identify the make and model - sort of. (The car is... yellow. )

I can see how this composite can be misleading, but I still think it was cleaver of the photographer to make the spiral around a different star from Polaris.

As people have commented, I think the composite can be misleading, too. And I commented on SpaceWeather.com site (posted before APOD) and discussed on that point with the contributor by private e-mail.

By the way, without "including a landscape", making a spiral around a different star from Polaris to reproduce a startrail in the far past or future has already been done in 1974 by Mr. Yukio Hiramatsu in a single-shot exposure using a film camera.
( http://www.hamamatsu-space-hunters-club ... _page.html ... This is a Japanese site, and the 5th photo from the top is B.C. 3000 diurnal motion reproduction.)
Detailed system configuration is unknown, but he seemed to use a similar double-guide system, because it requires two independent rotary systems to fix a different star from Polaris and to rotate other stars around the fixed star. Hiramatsu took the photo in 20 minutes and every trail has about 5 degrees, so the second guide's speed seems to be the same as a usual guide. He won the Grand Prize for the Best Idea in a monthly magazine "Ten-mon Guide" (Astronomical Guide) July 1974. And the editor said, "This photo can puzzle the future archaeologists."

Hiramatsu's photo does not contain any landscape, because it was taken by a film camera in a single shot, so it is easier than Miguel's composite with a landscape.
But I feel an anxiety that Miguel's one could mislead people to misunderstand that the future celestial north pole shifts in the sky due to including landscape.

[neufer]

• • Boyhood (2014)

Mason Evans, Jr. (Coltrane): In a few years ... that will be me:

Univ. of Texas professor talking to himself at diner:

• • A star map. A map
    of heavenly bodies as accurate ...
    that could plot the position of the
    North Star 14,000 years later ...
    and future generations ..

[paragkulkarni]

And what happens to URSA MAJOR at that time.
It loses its great bear shape.

[neufer]

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.

And what happens to URSA MAJOR at that time.
It loses its great bear shape.

• Its great "bear" shape?
  
  "When I see a bird that walks like a duck and swims like a duck
  and quacks like a duck, I call that bird a duck."
  • - Indiana poet James Whitcomb Riley (1849–1916)

<<Even 25,000 years from now, the Big Dipper pattern will look nearly the same as its does today. Astronomers have found that the stars of the Big Dipper (excepting the pointer star, Dubhe, and the handle star, Alkaid) belong to an association of stars known as the Ursa Major Moving Cluster. These stars, loosely bound by gravity, drift in the same direction in space. In 100,000 years, this pattern of Big Dipper stars (minus Dubhe and Alkaid) will appear much as it does today!>>

[Chris Peterson]

And what happens to URSA MAJOR at that time.
It loses its great bear shape.

Yeah, right. Assuming it ever did look like a bear.

[timetraveller]

"... star trails reminiscent of the year 14000 CE" is incorrect. You can only reminisce about past events. These star trail are reminiscent of the year 12000 BCE.

The year 14000 is in the past... just not yet...

[starsurfer]

And what happens to URSA MAJOR at that time.
It loses its great bear shape.

Yeah, right. Assuming it ever did look like a bear.

I can see the bear!

[neufer]

"... star trails reminiscent of the year 14000 CE" is incorrect.

You can only reminisce about past events. These star trail are reminiscent of the year 12000 BCE.

• Star trails prescient of the year 14000 CE?

Or possibly (considering all the objections stated thus far):

• Star trails oblivious of the year 14000 CE.

[john Erickson]

I think using one camera mount to "stop" the rotation of the Earth, and another camera mount to "restart and reposition" the axis of rotation to line up with another star is a very clever exercise, even if it does not give results that match up with landmarks on the horizon for some other era. I think the horizon in the second photo must have been doctored or transplanted from the first photo because the camera must have been moving relative to the horizon. If I am right, I would like to see the undoctored photo.

[neufer]

and the South pole is void of a star ?

For the moment, yes. At least, one bright enough to be useful.

Sheffield Astronomical Society Newsletter (1994)
by Kieron Taylor.

<<At present, the neighbourhood of the South celestial pole is rather devoid of bright stars. The South pole is marked by the 5.5 magnitude star Sigma Octans, barely visible to the naked eye. In the year 4200 AD, the 4.1 magnitude star Gamma of the constelation Chameleon will be less than 2° from the pole. In the year 5800 the 3.6 magnitude star Omega Carinae will be less than a degree from the South celestial pole. There are a number of second or third magnitude stars in this region of the sky, many of which will pass close to the pole. In the year 8100 the 2.3 magnitude star Aspidiske, again in the constelation Carina, will be the pole star, followed in 9200 by the magnitude 2.0 star Delta Velae. (By now the Milky Way is crossing the South pole, so the neighbourhood is studded with a number of moderately-bright stars, many of which take their turn at holding the honour of being Pole Star.) Around the year 14,000 AD, while Vega is marking the North Celestial Pole, Canopus, the second brightest star in the sky, will be within 10° of the South Pole ; and around the year 22,000 AD the 0.5 magnitude star Achernar, in the constelation Eridanus, will have a South declination of about 82½°.>>