APOD: Star Size Comparisons (2011 Feb 22)

[Hok]

I just wondered - it would take 1100 years for jet plane to orbit that giant star - but how long would it take the Earth to orbit that star if it was at the same distance from it as it is from our Sun?

The distance between Earth and Sun (150 million km) is much smaller compared with the size of that star (approx. 3 billion km). So if you mean the distance between centers of gravity, Earth would orbit well inside the star. If you mean the distance between surfaces, Earth would probably still be in the outer layers of the star, which would still be quite uncomfortable

In order to compute the speed of a real orbit of Earth we'd have to know the mass of the star.

[Ann]

I just wondered - it would take 1100 years for jet plane to orbit that giant star - but how long would it take the Earth to orbit that star if it was at the same distance from it as it is from our Sun?

Well, if my calculations are correct (and they may be totally wrong) the Earths moves around the Sun at a velocity of about 107,500 kilometers per hour. I think that means that we would have to fly about 119 times faster than that 900 kilometer per hour plane in order to fly at the same speed that the Earth orbits the Sun. So I guess that if we flew 119 times faster than 900 kilometers per hour, that means that it we would go around that star 119 times faster than 1,100 years. If my calculatons are correct, it would only take us a little more than nine years! (But somebody had better check my calculations!)

Ann

[spanner in the works]

The video ends by telling us that we are not the centre of the universe. Of course, we are! Firstly the unverse is not a sphere and does not have a centre as we conventionally think of it. Most of us are incapable of imagining multidimensional hyperspace so let's stick with what we can imagine. Since we can see (including non-visual instrumentation) equally far in all directions, we are at the centre of our universe! This is also true for every other possible observer throughout the universe! In other words, everywhere is the centre of the universe. Isn't equality great!!

[Antony]

Surely the centre of the Universe is the point at which the "Big Bang" went ... BANG! Has anyone attempted to estimate where in the observable universe this point might be?

This shows a misunderstanding of the nature of the Big Bang. BB wasn't some kind of explosion from a single point, surrounded by 3D space; if I understand correctly, it was the mathematically-deduced singularity of space-time, where all of 3D-space coincided at a single point, and where space (and time) originated. The "location" of BB is not merely undiscoverable, it is not even definable in any scientific way.

This is why all points in the Universe have an equal claim (or non-claim) to be at the centre. From the moment of the BB, every point is observed as flying rapidly away from every other point, no matter what observation frame is chosen.

[Rusty Brown in Canada]

To state in plain English what others have pointed out in obscure language: the Earth is turning backwards!

[neufer]

WHERE is Uranus? It's mysteriously gone missing!?

Neptune & Uranus are basically twins in size and appearance; the video is about differences.

[Pilliwinks]

The video ends with a reminder that we are not the center of the universe (even though we all think we are.) The National Lampoon said it best in their LP, Radio Dinner, 1972:

You are a fluke of the universe.
You have no right to be here.
Whether you can hear it or not
the universe
is laughing behind your back.

[neufer]

I just wondered - it would take 1100 years for jet plane to orbit that giant star - but how long would it take the Earth to orbit that star if it was at the same distance from it as it is from our Sun?

The distance between Earth and Sun (150 million km) is much smaller compared with the size of that star (approx. 3 billion km). So if you mean the distance between centers of gravity, Earth would orbit well inside the star. If you mean the distance between surfaces, Earth would probably still be in the outer layers of the star, which would still be quite uncomfortable

In order to compute the speed of a real orbit of Earth we'd have to know the mass of the star.

The mass is approximately 36 times that of the sun; if most of the mass is still below the Earth then it orbits in about 2 months (as compared with about 5 years if the Earth was nearer to the surface of the star.

[nnocd]

The colors you see on Earth are hindered by the atmosphere on the Earth. To me, Everyone is taking this all too literally. It was meant to show you size, not color or temperature. Have a nice Day.

[jrjanzen]

From my knowledge of Relativity, the last statement is incorrect. We are just as accurate in saying WE are the centre of everything, as we are in saying any point in space is equally legitimately also the centre of everything. This is one of the quirks of General Relativity, is it not?

[osh]

The rotation problem is easy... North is South. All the planets are upside down as seen through a telescope....

[neufer]

The rotation problem is easy... North is South. All the planets are upside down as seen through a telescope....

But they clearly aren't.

The rotation problem is easy... the planets are simply being displayed.

They wouldn't be orbiting at the same speed in any event
(and Venus does, in fact, rotate in that direction).

[royhrod]

How does relative star size or quantity of stars have anything to do with whether or not we are at the center of the universe?

Other than that issue/question, it was a very impressive clip.

[orin stepanek]

Great APOD today! Creating a lot of discussion! Makes one feel small in the universe.

[rfbrown8309]

Mistakes I saw in my first pass: Planets and stars aren't technically "floating." Planets are spinning wrong way. Saturn has no rings (as the sign says). Not sure the color of Mercury is correct. Venus atmosphere is missing.
Asserting that we are not the center of the universe: Is there a center? How do you find the center of a 4-dimensional space-time continuum? Isn't every point technically the center?

[fallofrain]

Heavy thought for the day..."We are the Universe beginning to think about itself."

[Edward]

FWIW, I compiled a top 5 animations a while back: http://labs.fieldofscience.com/2009/11/ ... s-and.html

[Peanuts Reloaded]

Some months ago the video inspired me a comic strip (sorry, in Italian) with Snoopy and his Sopwith Camel:
http://www.flickr.com/photos/steveb59/5468035367/

[Chris Peterson]

Surely the centre of the Universe is the point at which the "Big Bang" went ... BANG! Has anyone attempted to estimate where in the observable universe this point might be?

The Big Bang didn't occur at a 3D point, it occurred at a 4D point, which is now outside the 3D universe (because it occurred at t=0, and now we have t>0). Presumably, every 3D point in the Universe is equidistant from the 4D point where the BB occurred, although there are other models that allow for different points to be different distances from the origin. In any case, however, it is reasonable to say that every point we can observe in the Universe can be treated as the center from a three-dimensional viewpoint.

[dmbeaster]

"Center of the Universe" discussions.

There is no known center, nor is it correct to think of the Big Bang as strictly a point source. We are, by definition, the center of the observable universe. However, there is no evidence that the observable universe matches the actual dimensions of the universe in its entirety (whatever that may be).

In all directions that we look, the universe appears the same. Either by some incredible coincidence, we just happen to be located very near or at the center, or what we are observing is one patch of the larger universe. There is no known means to determine what lies beyond the observable universe, and over time, the outer limit of what we can observe now will fade outward into the unobservable universe so long as the expansion of the universe remains constant or is accelerating. This is due to the odd fact that the expansion of the universe allows objects separated by a great enough distance to at some point recede from one another at a rate exceeding the speed of light, even though the objects themselves are not moving at that speed.

Assuming the larger universe exceeds the observable universe, the Big Bang would consist of all space erupting - not a point source. We can only see a part of it. By definition, the part that we can see would be a point source in the a larger eruption. Hence, the Big Bang is frequently described as an eruption of all the observable universe from a point source, but that is correct provided that the qualifier "observable universe" is always applied.

[alphachap]

I just wondered - it would take 1100 years for jet plane to orbit that giant star - but how long would it take the Earth to orbit that star if it was at the same distance from it as it is from our Sun?

In that case the Earth would be inside the star.

[PHook]

@ alNilam: Wouldn't the name actually be "an Nilam"? There should be assimilation of the "l" of the article "al" to the first consonant of "Nilam".

[Chris Peterson]

There is no known center, nor is it correct to think of the Big Bang as strictly a point source. We are, by definition, the center of the observable universe. However, there is no evidence that the observable universe matches the actual dimensions of the universe in its entirety (whatever that may be).

There is, however, evidence that the Universe is larger than the observable Universe.

In all directions that we look, the universe appears the same. Either by some incredible coincidence, we just happen to be located very near or at the center, or what we are observing is one patch of the larger universe.

That's not quite right. There is no place in the Universe (observable or otherwise) that could be considered the center.

Assuming the larger universe exceeds the observable universe, the Big Bang would consist of all space erupting - not a point source. We can only see a part of it. By definition, the part that we can see would be a point source in the a larger eruption. Hence, the Big Bang is frequently described as an eruption of all the observable universe from a point source, but that is correct provided that the qualifier "observable universe" is always applied.

I've never seen the Big Bang described that way, except in error. The BB is not an expansion from a 3D point, and the geometry of the expansion is not in any way related to the concept of the observable Universe. The BB is an expansion of spacetime that began at a 4D point, and that 4D point is not observable, because we can't move backwards in time. We are riding on the 3D surface of that expansion, with the origin in a direction we are incapable of seeing.

[rstevenson]

... there is no evidence that the observable universe matches the actual dimensions of the universe in its entirety (whatever that may be).

In a recent thread here it was mentioned that the size of the universe has been calculated to be between 251 and 398 times the size of the observable universe. But that was only according to a model which assumes the universe is closed.

Rob

[dmbeaster]

Chris:

Concerning your last point about the nature of the Big Bang, read this. http://www.atlasoftheuniverse.com/bigbang.html
I think your description concerning 4d vs 3d is misleading, nor are your criticisms of my remarks accurate. I did not indicate that the Big Bang expansion is an expansion from a 3d point - it was all of space erupting. Nor did I state that the expansion and the observable universe are linked concepts (though they are in one general sense - the limitation on what we can observe is due to expansion). What is correct that in terms of what we can observe, the expansion appears to be radiating outward everywhere from us in the observable universe. That can lead to the misperception that we are at some kind of "center," but only if the observable and actual universe are coincident.

As a thought experiment, imagine what an observer on the most distant galaxy that we can see would be observing as of now. The best assumption from what we know of the universe (flat and infinite) is that the view would be essentially identical to our view, except his observable universe would be almost entirely outside of what we observe. An then imagine what an observer on an equally distant galaxy would observe, but which is located in the exact opposite direction. Again, the best assumption is that the view would be the same. And both of those observers would never be able to observe the other provided that the expansion is constant or increasing. And you can repeat the thought experiment from the point of view of our imaginary observers, and create additional imaginary observers further removed from our observable universe.

Presumably, there are in infinite number of "observable" universes for each potential hypothetical observers. I dont think cosmology currently provides a known answer to this question. It is still just conjecture (such as multi-universes or multiple Big Bangs).