APOD: Star Size Comparisons (2011 Feb 22)

[neufer]

2.800.000.000 km of diameter are 61 trillion km of circumference, flying at 900 km/h, ¿and only in 1100 years?

¿Pi = 31416?

[Alnilam]

@ 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".

Thank you for your interest in my pseudo.

We have a good book about arabian names of stars (in French of course !) : "Heritages Arabes - Des noms arabes pour les etoiles" (something like "Arabs Heritage - Arabic names for stars"). The author, Roland Lafitte, is a great specialist of this subject and widely of old representations of Sky in ancient cultures (arabic, persian, hindu, chinese, etc...). He started as member of the SELEFA society which purpose is to study arabic origins of numerous French words. And so, they found the "mine" of stars names and Roland Lafitte dug deeper, completing the studies of the german Paul Kunitzsh (he published in 1959 a list of 210 arabian names of stars with their correct ethymology) . You can have a look of his works in this site (English version) :

http://www.uranos.fr/PRES_EN.htm

In his book, the name "Alnilam" (also "Alnitam") is defined by Piazzi and comes from "al-Nizam", something like "the row" initialy refering to the three stars (Alnitak, Alnilam, Mintaka) of Orion Belt.

Also defined by Piazzi, "Mintaka" comes from "Mintaqa al-Jawsâ" (about "Elgeuze belt") and "Alnitak" from "Nitâq al-Jawsâ" (about the same). All these names refer to a great constellation named "al-Jawsâ" (transposed as "Elgeuze" in French, something like "the wife") that arabians placed about Orion in the Sky but much larger than Orion (her bow, pointing East, encloses somes stars of Gemini and Monoceros). In fact, about half of arabic stars names came from a specific arabic representation of the Sky, and the others came from arabic translations of Greek names (directly linked with the position of stars in the Greek constellations, by exemple : Deneb as "the tail" of Cygnus), all these names representing about two third or more of stars names (the other are based on Latin, and sometimes are very bad translation from arabic words).

There is a drawing of "al-Jawsâ" in p12 of this document (from the Uranos site) :

http://www.uranos.fr/PDF/SKY.pdf

[randbpaton]

the earth is rotating in the wrong direction!

[alphachap]

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?

When we talk about the expansion of the universe, we are really talking about contraction of matter. Looking from another point of view is often helpful. Those 2 points of view are probably equivalent, but maybe they are not, in which case it would be nice to know which is more correct.
In the expanding universe point of view, going back in time until the Big Bang, we get the whole of space concentrated in a point, that point is the whole of space, so that Big Bang point is everywhere in space.
In the contracting matter point of view, which I prefer, going back in time until the Big Bang, we get matter expanding until all matter overlaps and every atom spans the whole universe. So the Big Bang is everywhere, it is not a point.
Also general relativity teaches us that space and time can not be separated, and that space evolving in time is a fiction. What we have is spacetime, fixed, immutable.

[xcjorr]

The center of the Universe is at t=0.

If we back 4D time out and acknowledge the fact that the universe is becoming spatially, wouldn't it still be possible to identify at least the region of 3D space at the center of the 3D universe? Or, are we so limited by our understanding of the known universe due to our limited technology (every direction is as far away and relatively uniform as all others) that we can't even hazard a guess as to where this 'center of the center' is? That is, since we can't tell where the boundaries of '3D becoming' are (if it exists) so we can't extrapolate even a hazy 'center of the center'?

[geddyme]

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?

Good question. The most widely accepted data on the size of this star suggests it would nearly encompass the orbit of Saturn if it's center were placed at the center of our sun. From what I've been able to deduce the Earth travels at roughly 3X the speed of Saturn on average during it's sojourn around our star. Now lets assume that "nearly encompassing" the orbit of Saturn equates to, say within 93 million miles (the avg earth to sun distance) of Saturn's orbital path.

Saturn orbits our star every 10755.7 earth days. Thus 10755.7/3 = 3,385.2 days _OR_ 9.82 yrs _OR_ nine earth years and until Oct 27th around 7pm local time of the tenth year for the Earth to complete an orbit at Saturn's average orbital distance from the center of this star. I just did this in my head so I simplified it a lot, got a little carried away at the end, but roughly that is what you are looking at. Obviously the Earth would be inside this monster if this star suddenly appeared at the center of our solar system, and thus completely annihilated. Is it possible that 93 million miles from this beast is not far enough for our blue planet to avoid being collected by it's gravity, and for all intents and purposes becoming part of VY Canis Majoris?

[10Degree]

If size is the topic of the video, let's talk size. If our sun was replaced with this big-dog star with a diameter of 2.8 billion km, it would engulf all planets out to and including Saturn. That's big my friends!

[Guest]

Should have shown a couple of brown dwarfs, since they are intermediate in size, and some red dwarfs, since they are by far the most common type of star.

[ascet]

at the end of the video, instead of zooming in on the largest star and show a tiny dot in place of planet earth i would like to see the largest
star be placed in our solar system and see how much place it will occupy if placed there.

[Beta Lyrae]

In order for something to orbit VY Canis Majoris near its surface:

mass_solar = 1.989e30 kg
radius_vy = 2.8e9 km = 2.8e12 m
mass_vy = 35 * M_solar = 6.962e31 kg
G = 6.674e-11
specific force = G * mass / (radius^2) = 5.93e-4 N/kg
specific centripetal force = velocity^2 / radius
velocity = sqrt(specific_centripetal_force * radius) = 4.07e4 m/s.

About 40.7 km/second or 147,000 km/hour, according to my calculations. This would make it travelling 164 times faster. The pull of gravity near the star's surface is only 0.000064 gee.

[jr chaffer]

This is a nice show - but just one more of many such entertaining depictions. It is pretty enlightening to those who are completely unfamiliar with astronomy and astrophysics.

BUT - there is no need at all for the superfluous, unjustified, in fact rather silly, philosophical statement at the end. There is simply no evidence to justify such a claim - real or otherwise.

[Chris Peterson]

When we talk about the expansion of the universe, we are really talking about contraction of matter. Looking from another point of view is often helpful. Those 2 points of view are probably equivalent, but maybe they are not, in which case it would be nice to know which is more correct.

That's not the case. Matter is not contracting. Atoms are the same size they always were. Space is expanding, except where there are fields strong enough to hold it together- gravitational fields, nuclear force fields, etc. The distance between pieces of matter is what is increasing.

[Chris Peterson]

If we back 4D time out and acknowledge the fact that the universe is becoming spatially, wouldn't it still be possible to identify at least the region of 3D space at the center of the 3D universe?

No. First of all, the Universe isn't "becoming"; it is expanding. In the 3D universe, there is simply no center. Any point can be considered the center of 3D expansion, and the actual point of expansion of the entire Universe is at t=0, which is in a direction we can't look. Go back to the balloon analogy, which is very good. In that case, the surface of the balloon is the spatial universe, but the expansion is from a point inside the balloon. If you are a 2D being living on the surface of the balloon, there is no way you can see the center. But on your surface, everything is moving away from you. You are a center of expansion, even if you are not the center of the 3D universe. There is nothing special about any place on the balloon surface.

Our inability to see the true center of expansion is not a technological limitation.

[ultradeep]

Saturn is depicted as a sphere, about as spherical as the other objects listed. However, it is a quite oblate spheroid; its equatorial diameter is about 10% greater than its axial diameter.

[astrocycle]

There were a number of points made about supergiant stars being aspherical, but we do know that the planets aren't. At the scale shown, Saturn's oblateness would be easily seen:
http://en.wikipedia.org/wiki/File:Satur ... ope%29.jpg

And, despite the perspective view from the observer, to me the video shows Venus to be smaller than the earth. At the scale shown, the difference in sizes would be imperceptible.

The rest , except for that inane comment at the end could be chalked up to artistic license.

[Just Some Guy]

It would take you much longer than 1100 years to circle that star.
It would take you at least half that time to get through the TSA.

[alphachap]

When we talk about the expansion of the universe, we are really talking about contraction of matter. Looking from another point of view is often helpful. Those 2 points of view are probably equivalent, but maybe they are not, in which case it would be nice to know which is more correct.

That's not the case. Matter is not contracting. Atoms are the same size they always were. Space is expanding, except where there are fields strong enough to hold it together- gravitational fields, nuclear force fields, etc. The distance between pieces of matter is what is increasing.

How do we know? What if matter is contracting everywhere? The distance between pieces of matter would appear to increase.

[owlice]

What if matter is contracting everywhere?

If it's going to contract everywhere, can it start on my hips, please?

[Chris Peterson]

That's not the case. Matter is not contracting. Atoms are the same size they always were. Space is expanding, except where there are fields strong enough to hold it together- gravitational fields, nuclear force fields, etc. The distance between pieces of matter is what is increasing.

How do we know? What if matter is contracting everywhere? The distance between pieces of matter would appear to increase.

Contracting matter is inconsistent with both theory and observation. For instance, if spacetime were of fixed size and matter shrinking, we'd not see cosmological redshift, which is caused by the expansion of space as light travels through it.

[Indigo_Sunrise]

If it's going to contract everywhere, can it start on my hips, please?

[EarthBoy]

While it's understandable to start with the planets of our solar system, and our star, "The Sun", this size list,by sequence, there by implies that our Sun is the smallest star – which is also not true

So I would suggest including smallest, or smaller stars, in the list too…

Of course that brings it's own set of confusions…

It would also be interesting to list the 'smallest planet' (definition: must be spherical), (largest planet), 'smallest neutron star', 'largest neutron star', 'smallest black hole', largest ' (currently known) black hole, and size of our milky-way galaxy, as a basis of comparison.

As for the other discussion, I can't see why our Universe should not be semi-spherical…
of course we are lost way inside it somewhere… (reasonably nice)…

[neufer]

While it's understandable to start with the planets of our solar system, and our star, "The Sun", this size list,by sequence, there by implies that our Sun is the smallest star – which is also not true

So I would suggest including smallest, or smaller stars, in the list too…

Of course that brings it's own set of confusions…

It would also be interesting to list the 'smallest planet' (definition: must be spherical), (largest planet), 'smallest neutron star', 'largest neutron star', 'smallest black hole', largest ' (currently known) black hole, and size of our milky-way galaxy, as a basis of comparison.

Well, one could reasonably have left out black hole event horizons all together.

However, relative to the sun neutron stars are 100,000 times smaller
whereas the largest stars are only 2,000 times larger than the sun.

The emphasis on how big stars can get vis-a-vis the earth & sun
would have gotten lost by going in the other direction.

[chad2424]

I would love to see you add in some smaller stars like red dwarfs and white drawfs for comparison.

That would be cool

[neufer]

I would love to see you add in some smaller stars like red dwarfs and white dwarfs for comparison.

Brown dwarfs are a little bit bigger than Jupiter.
White dwarfs are a little bit bigger than the Earth.

[guest]

We are the center of the observable univers, arent we.

So is everybody else, whereever he may be in the universe.