APOD: When Vega is North (2015 May 08)

Comments and questions about the APOD on the main view screen.
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APOD: When Vega is North (2015 May 08)

Post by APOD Robot » Fri May 08, 2015 4:08 am

Image When Vega is North

Explanation: In only about 12,000 years Vega will be the North Star, the closest bright star to our fair planet's North Celestial Pole. By then, when you fix your camera to a tripod long exposures of the night sky will show the concentric arcs of star trails centered on a point near Vega as Earth rotates on its axis. Of course, presently the bright star conveniently near the North Celestial Pole is Polaris, but that will change as the Earth's axis of rotation precesses, like the wobble of a spinning top with a precession period of about 26,000 years. If your camera is ready now and you don't want to wait 12,000 years for Vega to be the North Star, consider this ingenious demonstration of contemporary star trails (left) versus star trails reminiscent of the year 14000 CE. Both were recorded this April at the Alqueva Dark Sky Reserve in Alentejo, Portugal. To produce the more Vega-centric star trails of the distant future, astronomer Miguel Claro combined the rotation of two startracking camera mounts to create the apparent shift in planet Earth's North Celestial Pole.

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Re: APOD: When Vega is North (2015 May 08)

Post by Ann » Fri May 08, 2015 4:09 am

Vega should be a splendid North star, brighter than Polaris and dazzlingly blue-white! :D

Interesting picture. Thanks.

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Re: APOD: When Vega is North (2015 May 08)

Post by G Sitja » Fri May 08, 2015 5:14 am

Unfortunately this "ingenious demonstration" is "dangerous" as the picture shows situations where Earth axis changed "independently" from the planet ! Watching this image, some may believe that North ant South pole change geographic position on Earth which is totally false. In the picture, Vega and concentric circles around it should bee seen at the same position as Polaris now in the representations, leading to very close images.

Atas

Re: APOD: When Vega is North (2015 May 08)

Post by Atas » Fri May 08, 2015 5:24 am

G Sitja wrote:Unfortunately this "ingenious demonstration" is "dangerous" as the picture shows situations where Earth axis changed "independently" from the planet ! Watching this image, some may believe that North ant South pole change geographic position on Earth which is totally false. In the picture, Vega and concentric circles around it should bee seen at the same position as Polaris now in the representations, leading to very close images.
good point!

Sebastien

Re: APOD: When Vega is North (2015 May 08)

Post by Sebastien » Fri May 08, 2015 5:34 am

@G Sitja, exactly. I think he's overlooked that shift in the landscape or needed it to make the principle more understandable.
It shows a shift in the landscape that won't happen. As would a spinning top not only wobble (precession) but also change it physical rotational axis (other than the initial one).

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Re: APOD: When Vega is North (2015 May 08)

Post by revloren » Fri May 08, 2015 6:53 am

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?

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Re: APOD: When Vega is North (2015 May 08)

Post by PTW » Fri May 08, 2015 7:46 am

This picture is disastrously misleading, and needs to be redone.

Maciej Zapior

Re: APOD: When Vega is North (2015 May 08)

Post by Maciej Zapior » Fri May 08, 2015 8:44 am

PTW wrote:This picture is disastrously misleading, and needs to be redone.
I agree.

tao

Re: APOD: When Vega is North (2015 May 08)

Post by tao » Fri May 08, 2015 10:17 am

G Sitja wrote:Unfortunately this "ingenious demonstration" is "dangerous" as the picture shows situations where Earth axis changed "independently" from the planet ! (...) In the picture, Vega and concentric circles around it should be seen at the same position as Polaris now in the representations, leading to very close images.
My thoughts exactly. :shock:

Laura Lee

Re: APOD: When Vega is North (2015 May 08)

Post by Laura Lee » Fri May 08, 2015 10:23 am

Wouldn't it be prescient rather than reminiscent? And yes, it should look the same as it does now: north will still be north here on planet Earth.

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Re: APOD: When Vega is North (2015 May 08)

Post by starsurfer » Fri May 08, 2015 11:12 am

Obviously it can't be 100% exact but I think this is an interesting vision of the future that at least lends itself well to a discussion about precession.

Also what about Canopus?

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Re: APOD: When Vega is North (2015 May 08)

Post by PTW » Fri May 08, 2015 11:23 am

starsurfer wrote:Obviously it can't be 100% exact but I think this is an interesting vision of the future that at least lends itself well to a discussion about precession.
It's completely wrong and, because of that, lends itself extremely badly to a discussion about precession.

This isn't a case of "splitting hairs". To be correct, the picture would have the stars circling about the same point with respect to the ground features. The only things that will affect where the rotation point is in the picture are polar motion and continental drift.

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Re: APOD: When Vega is North (2015 May 08)

Post by Jarod997 » Fri May 08, 2015 1:13 pm

Ya, ok, the axis of rotation is off, but the idea is right. He's spinning the stars around where Vega is right now, trying to simulate what it would look like in a few thousand years.

I still say the photographer gets points for creativity - I think the image is really well done, even if it's a little off.

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Re: APOD: When Vega is North (2015 May 08)

Post by somebodyshort » Fri May 08, 2015 1:25 pm

revloren wrote: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?
I think the seasons move around a cycle every 26,000 years. I don't know forwards or backwards.

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Re: APOD: When Vega is North (2015 May 08)

Post by somebodyshort » Fri May 08, 2015 1:31 pm

Is precession and Earth's rotation affected by things like ice ages. I would think that as ice melts and mass moves to the equator the conservation of momentum would cause the rotation to slow down. During an ice age rotation would speed up. Makes predicting that far out difficult.

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Re: APOD: When Vega is North (2015 May 08)

Post by PTW » Fri May 08, 2015 2:22 pm

Jarod997 wrote:even if it's a little off
It's not "a little off": it's totally the wrong idea.

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Re: APOD: When Vega is North (2015 May 08)

Post by drollere » Fri May 08, 2015 2:24 pm

this "ingenious" picture is an appalling piece of pseudoscience. the fact that some posters here don't clearly see why confirms the confusion this "document" will create.

clearly, the APOD editorial fascination with star trail photographs has overruled better judgment. take the photo down now, or change the caption content to point out that it is a ludicrous fabrication.

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Re: APOD: When Vega is North (2015 May 08)

Post by geckzilla » Fri May 08, 2015 4:09 pm

drollere wrote:this "ingenious" picture is an appalling piece of pseudoscience. the fact that some posters here don't clearly see why confirms the confusion this "document" will create.

clearly, the APOD editorial fascination with star trail photographs has overruled better judgment. take the photo down now, or change the caption content to point out that it is a ludicrous fabrication.
Calm down. Being wrong doesn't make it pseudoscience. Illustrate and/or communicate your thoughts clearly on why you think it's wrong. If it's really that confusing then we could use some extra help here understanding where it went wrong.
Just call me "geck" because "zilla" is like a last name.

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Re: APOD: When Vega is North (2015 May 08)

Post by Donnageddon » Fri May 08, 2015 4:26 pm

If one ignores the common use of a planetary foreground for concentric arc star trail pictures, it is a fine, and ingeniously created comparison.

If one cannot ignore the admittedly incorrect relationship of the foreground to the 14000 year projected star field arc trails, then it might lead to hyperbolic denunciations.

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Re: APOD: When Vega is North (2015 May 08)

Post by Chris Peterson » Fri May 08, 2015 5:17 pm

revloren wrote: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).
Chris

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Re: APOD: When Vega is North (2015 May 08)

Post by Ron-Astro Pharmacist » Fri May 08, 2015 5:19 pm

You just have to use your imagination. The homes on the right are retro from 12,000 years before (they used this APOD from their old quantum computer archive in the year 14,000) and were rebuilt in a more northerly location being careful to obtain very similar vegetation. Quite well done actually. What did everyone expect – that those homes would still be there?

They would have built at the same site but the APOD Archival Museum will sit there in the future chosen to commemorate of one of its most notorious Photos of the Day. :wink:
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Re: APOD: When Vega is North (2015 May 08)

Post by Chris Peterson » Fri May 08, 2015 5:20 pm

somebodyshort wrote:Is precession and Earth's rotation affected by things like ice ages. I would think that as ice melts and mass moves to the equator the conservation of momentum would cause the rotation to slow down. During an ice age rotation would speed up. Makes predicting that far out difficult.
Ice and its effects on land do very subtly affect our rotation and possibly even orbital parameters. But it's an extremely small effect. Measurable with modern tools, but not something that has to be considered in looking at the timing of precessional cycles.
Chris

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Re: APOD: When Vega is North (2015 May 08)

Post by Jarod997 » Fri May 08, 2015 6:33 pm

PTW wrote:
Jarod997 wrote:even if it's a little off
It's not "a little off": it's totally the wrong idea.
Explain - and please, planetary science isn't my first subject - try to use simpler terms.

Steven Morris

Re: APOD: When Vega is North (2015 May 08)

Post by Steven Morris » Fri May 08, 2015 6:41 pm

"... 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.

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Re: APOD: When Vega is North (2015 May 08)

Post by Chris Peterson » Fri May 08, 2015 6:41 pm

Jarod997 wrote:
PTW wrote:
Jarod997 wrote:even if it's a little off
It's not "a little off": it's totally the wrong idea.
Explain - and please, planetary science isn't my first subject - try to use simpler terms.
If you were at that location on the Earth, the north celestial pole would not change where it is in the sky. It is always directly over the north pole, and that is always at the same horizon coordinates (altitude and azimuth). The image gives a false impression that in 12,000 years the pole will be in a different place in the sky. The stars will be in different places, but that's all. Vega will be close to where Polaris currently is.

Basically, both images here should look almost identical. In fact, if you wanted to emphasize how the sky changes with time, a star trail image (real or synthesized) is not a good way of doing it. To our eyes, all star trail images look similar- we lose the pattern of the stars.
Chris

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