APOD: Star Size Comparison 2 (2018 Jun 12)

Comments and questions about the APOD on the main view screen.
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Re: APOD: Star Size Comparison 2 (2018 Jun 12)

Post by ta152h0 » Tue Jun 12, 2018 3:45 pm

All my transistors just released all factory smoke contained within
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jpepper

Re: APOD: Star Size Comparison 2 (2018 Jun 12)

Post by jpepper » Tue Jun 12, 2018 3:50 pm

Placing HD 100546b as one of the largest possible planets may be technically correct, but is a bad choice. It has no mass measurement so has not been confirmed as a planetary-mass object, and the radius measurement is very uncertain. A better choice would be HAT-P-67b, which is the largest object known to be planetary mass with a reliably measured radius. At 2.09 R_J it is less impressive, but more accurate and less misleading.

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Re: APOD: Star Size Comparison 2 (2018 Jun 12)

Post by neufer » Tue Jun 12, 2018 4:44 pm

Chris Peterson wrote:
Tue Jun 12, 2018 2:34 pm
neufer wrote:
Tue Jun 12, 2018 12:52 pm

The crude structure at the edge of the known observable universe is basically the crude structure of the 372±14 kyr old cosmic microwave background radiation (CMBR).
It seems a little oxymoronic to state that the observable universe is currently 90 billion light years wide
since much of that current universe will never ever be observable.

(Also known universe is just easier to say.)
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Re: APOD: Star Size Comparison 2 (2018 Jun 12)

Post by BDanielMayfield » Tue Jun 12, 2018 4:54 pm

Ann wrote:
Tue Jun 12, 2018 3:27 pm
BDanielMayfield wrote:
Tue Jun 12, 2018 3:09 pm
BDanielMayfield wrote:
Tue Jun 12, 2018 2:27 pm
A suggestion for improvement would be to add more stars. A neutron star, a white dwarf and stars of each class up the MS would help it to be more balanced and informative, I think.
After rewatching the video I noticed the two smaller than our Moon solar system objects that where included to the left. A short further leftward jog down the distance scale to a city sized neutron star would be nice. White Dwarf stars might bracket Venus and Earth perhaps?

Then also, the caption on "the smallest possible star" needs to be corrected to 'the smallest Red Dwarf'.

Bruce
Perhaps "The smallest possible core hydrogen-fusing star"?

Ann
That would be accurate, but is the wording short enough? "Red Dwarf" is ok to me since they are significantly smaller than the Sun.

I'd personally drop the dwarf name for any star past above the knee of the MS. But, after seeing this vid I know that's a lost cause. In space there are no "normal" stars, only giants and dwarfs. :-?

A brown dwarf or two might also be included, but they're around the size of Jupiter. And, they tend to get smaller the more massive they are, I think.

Bruce
Last edited by BDanielMayfield on Tue Jun 12, 2018 5:10 pm, edited 1 time in total.
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Re: APOD: Star Size Comparison 2 (2018 Jun 12)

Post by Chris Peterson » Tue Jun 12, 2018 5:02 pm

neufer wrote:
Tue Jun 12, 2018 4:44 pm
Chris Peterson wrote:
Tue Jun 12, 2018 2:34 pm
neufer wrote:
Tue Jun 12, 2018 12:52 pm

The crude structure at the edge of the known observable universe is basically the crude structure of the 372±14 kyr old cosmic microwave background radiation (CMBR).
It seems a little oxymoronic to state that the observable universe is currently 90 billion light years wide
since much of that current universe will never ever be observable.

(Also known universe is just easier to say.)
"Known universe" is both incorrect, and contrary to standard usage. The radius of the observable universe can be stated in two common ways: 13.7 billion light travel years, or 45 billion comoving light years.
Chris

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mhuber

Re: APOD: Star Size Comparison 2 (2018 Jun 12)

Post by mhuber » Tue Jun 12, 2018 5:24 pm

Steve Basten wrote:
Tue Jun 12, 2018 5:45 am
Would an Inconsistency be that the video shows the known universe to be 90 Billion Light Years across?. This seems a little off considering we believe the universe to be 13.7 Billion Years old, with a maximum speed of travel being light itself. The universe of course could be bigger but the known observable Universe cannot be anywhere near 90 billion light years if all we can observe is 13.7 Billion Light years in all directions around us?
When observing an object that's a great distance away, for example, a galaxy 13 billion light-years away, you're seeing it's position as it was 13 billion years ago. Since the moment when the light that we see left that galaxy, it has continued to move away from us. Couple that with the expansion of space itself, and the observable universe is much larger than 13.7Gly in radius today. If one calculates the radius to be 45 Gly then the diameter would be 90 Gly. :)

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Re: APOD: Star Size Comparison 2 (2018 Jun 12)

Post by BDanielMayfield » Tue Jun 12, 2018 5:27 pm

There are several oxymoronic names and holdovers in astronomy. "Planetary nebulas" that have nothing to do with planets, etc.

Why do they do it? Tradition!
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Re: APOD: Star Size Comparison 2 (2018 Jun 12)

Post by BDanielMayfield » Tue Jun 12, 2018 5:47 pm

jpepper wrote:
Tue Jun 12, 2018 3:50 pm
Placing HD 100546b as one of the largest possible planets may be technically correct, but is a bad choice. It has no mass measurement so has not been confirmed as a planetary-mass object, and the radius measurement is very uncertain. A better choice would be HAT-P-67b, which is the largest object known to be planetary mass with a reliably measured radius. At 2.09 R_J it is less impressive, but more accurate and less misleading.
I like this comment. Where are the cutoffs in objects of "planetary mass" though?
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Re: APOD: Star Size Comparison 2 (2018 Jun 12)

Post by ems57fcva » Tue Jun 12, 2018 5:48 pm

Overall a good video, but one which obviously has its flaws. What I will comment on is what happens when it gets beyond showing the Milky Way and Andromeda. What comes up next are galaxies selected from the Hubble Deep Field. Those galaxies are easily over a billion light years away, be they appear before Laniakea, which is "only" 500 million light years across. What was needed instead was to show the Local Group, then the surrounding groups, then the Virgo supercluster (of which our local group is an outlying part), and then Laniakea. After this, the transition to the cosmic web was good.

Using 90 billion light years as the extent of the observable universe is acceptable. But all else after that point is purely speculation. If I was remaking this video, I would continue outward and slowly fade out with a note that the full extent of the universe is unknown. (Whether the extent in unknowable is a different matter. After all, you don't need to measure the whole Earth get a sense of how big it is.)

The business of the multiverse was not needed. At least the distance scale was gone. You are in different dimensions of existence when you start into the business, ones that may or may not exist. Going outside of the realm where the scale even makes sense just is not needed.(There is also the irony that the cosmic background is a leftover from when the universe was much smaller, and so is a lousy representation of how big it now is.)

It will be interesting to see what the next version looks like, if the creator is willing to listen to our criticisms and try again.

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Re: APOD: Star Size Comparison 2 (2018 Jun 12)

Post by Chris Peterson » Tue Jun 12, 2018 6:02 pm

mhuber wrote:
Tue Jun 12, 2018 5:24 pm
Steve Basten wrote:
Tue Jun 12, 2018 5:45 am
Would an Inconsistency be that the video shows the known universe to be 90 Billion Light Years across?. This seems a little off considering we believe the universe to be 13.7 Billion Years old, with a maximum speed of travel being light itself. The universe of course could be bigger but the known observable Universe cannot be anywhere near 90 billion light years if all we can observe is 13.7 Billion Light years in all directions around us?
When observing an object that's a great distance away, for example, a galaxy 13 billion light-years away, you're seeing it's position as it was 13 billion years ago. Since the moment when the light that we see left that galaxy, it has continued to move away from us. Couple that with the expansion of space itself, and the observable universe is much larger than 13.7Gly in radius today. If one calculates the radius to be 45 Gly then the diameter would be 90 Gly. :)
Actually, objects don't really move away from us. Space expands.
Chris

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stevewiggins

Re: APOD: Star Size Comparison 2 (2018 Jun 12)

Post by stevewiggins » Tue Jun 12, 2018 6:06 pm

Extrapolating "knowledge" into the unknown: other universes? Far-fetched literally. Bring it all back to the 'present' wherein the universe exists within the parameter of one planck second, or biblically "half time". Then one might begin to comprehend the true meaning of "billions of light years" and understand that what you're really seeing is within a chamber of one grand temple where other laws and ordinances prevail.

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Re: APOD: Star Size Comparison 2 (2018 Jun 12)

Post by neufer » Tue Jun 12, 2018 6:10 pm

Chris Peterson wrote:
Tue Jun 12, 2018 5:02 pm
neufer wrote:
Tue Jun 12, 2018 4:44 pm

It seems a little oxymoronic to state that the observable universe is currently 90 billion
light years wide since much of that current universe will never ever be observable.

(Also known universe is just easier to say.)
"Known universe" is both incorrect, and contrary to standard usage.
Why is known universe any more incorrect than observable universe when referring to
the current 90 billion light year wide universe most of which will never ever be observable :?:

"Observable universe" was standardized long before we knew about dark energy expansion.
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Re: APOD: Star Size Comparison 2 (2018 Jun 12)

Post by Chris Peterson » Tue Jun 12, 2018 6:12 pm

neufer wrote:
Tue Jun 12, 2018 6:10 pm
Chris Peterson wrote:
Tue Jun 12, 2018 5:02 pm
neufer wrote:
Tue Jun 12, 2018 4:44 pm

It seems a little oxymoronic to state that the observable universe is currently 90 billion
light years wide since much of that current universe will never ever be observable.

(Also known universe is just easier to say.)
"Known universe" is both incorrect, and contrary to standard usage.
Why is known universe any more incorrect than observable universe when referring to
the current 90 billion light year wide universe most of which will never ever be observable :?:

"Observable universe" was standardized long before we knew about dark energy expansion.
Because it isn't known, but it is observable.
Chris

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G Wolf

Re: APOD: Star Size Comparison 2 (2018 Jun 12)

Post by G Wolf » Tue Jun 12, 2018 6:16 pm

Thank you for posting that APOD Team.

This video is a nice addition to the various astronomical size comparison videos I've seen over the years. The addition of the solar system objects direct size comparison is a nice addition. It's the first time I've seen an asteroid included. The only thing I'd add would be Sedna or something else from the Kuyper Belt. Being an English major the only error I noticed was a grammar one. Instead of saying "there are many millions planets" I would have put "there are untold millions of planets." Or was it stars...?

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Re: APOD: Star Size Comparison 2 (2018 Jun 12)

Post by BDanielMayfield » Tue Jun 12, 2018 6:24 pm

ems57fcva wrote:
Tue Jun 12, 2018 5:48 pm
Overall a good video, but one which obviously has its flaws. What I will comment on is what happens when it gets beyond showing the Milky Way and Andromeda. What comes up next are galaxies selected from the Hubble Deep Field. Those galaxies are easily over a billion light years away, be they appear before Laniakea, which is "only" 500 million light years across. What was needed instead was to show the Local Group, then the surrounding groups, then the Virgo supercluster (of which our local group is an outlying part), and then Laniakea. After this, the transition to the cosmic web was good.

Using 90 billion light years as the extent of the observable universe is acceptable. But all else after that point is purely speculation. If I was remaking this video, I would continue outward and slowly fade out with a note that the full extent of the universe is unknown. (Whether the extent in unknowable is a different matter. After all, you don't need to measure the whole Earth get a sense of how big it is.)

The business of the multiverse was not needed. At least the distance scale was gone. You are in different dimensions of existence when you start into the business, ones that may or may not exist. Going outside of the realm where the scale even makes sense just is not needed.(There is also the irony that the cosmic background is a leftover from when the universe was much smaller, and so is a lousy representation of how big it now is.)

It will be interesting to see what the next version looks like, if the creator is willing to listen to our criticisms and try again.
These are very good observations. The unprovable multiverse notion is just pure conjecture. Fanciful Universes. No evidence at all.
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Guest

Re: APOD: Star Size Comparison 2 (2018 Jun 12)

Post by Guest » Tue Jun 12, 2018 6:29 pm

"this video is unavailable" appears on my browser. is anyone else seeing this? i'm located in the US.

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Re: APOD: Star Size Comparison 2 (2018 Jun 12)

Post by neufer » Tue Jun 12, 2018 6:30 pm

Chris Peterson wrote:
Tue Jun 12, 2018 6:12 pm
neufer wrote:
Tue Jun 12, 2018 6:10 pm
Chris Peterson wrote:
Tue Jun 12, 2018 5:02 pm

"Known universe" is both incorrect, and contrary to standard usage.
Why is known universe any more incorrect than observable universe when referring to
the current 90 billion light year wide universe most of which will never ever be observable :?:

"Observable universe" was standardized long before we knew about dark energy expansion.
Because it isn't known, but it is observable.
Many things about it are known by extrapolation from what is currently observable:
  • 1) its age & size
    2) its composition
    3) its flatness
    4) its general 3D structure (including a clear lack repeating structures)
It was a bit of a fudge when the term "observable universe" was
standardized in reference to the current 13.7 billion light year old universe.

Now that we know about dark energy expansion, however, a new term is clearly needed.
Art Neuendorffer

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Re: APOD: Star Size Comparison 2 (2018 Jun 12)

Post by Chris Peterson » Tue Jun 12, 2018 6:37 pm

neufer wrote:
Tue Jun 12, 2018 6:30 pm
Chris Peterson wrote:
Tue Jun 12, 2018 6:12 pm
neufer wrote:
Tue Jun 12, 2018 6:10 pm
Why is known universe any more incorrect than observable universe when referring to
the current 90 billion light year wide universe most of which will never ever be observable :?:

"Observable universe" was standardized long before we knew about dark energy expansion.
Because it isn't known, but it is observable.
Many things about it are known by extrapolation from what is currently observable:
  • 1) its age & size
    2) its composition
    3) its flatness
    4) its general 3D structure (including a clear lack repeating structures)
It was a bit of a fudge when the term "observable universe" was
standardized in reference to the current 13.7 billion light year old universe.

Now that we know about dark energy expansion, however, a new term is clearly needed.
I don't think so. Use whatever term you want. Or, you can use "observable universe" and be understood clearly.
Chris

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Re: APOD: Star Size Comparison 2 (2018 Jun 12)

Post by neufer » Tue Jun 12, 2018 6:54 pm

Chris Peterson wrote:
Tue Jun 12, 2018 6:37 pm
neufer wrote:
Tue Jun 12, 2018 6:30 pm
Chris Peterson wrote:
Tue Jun 12, 2018 6:12 pm

Because it isn't known, but it is observable.
Many things about it are known by extrapolation from what is currently observable:
  • 1) its age & size
    2) its composition
    3) its flatness
    4) its general 3D structure (including a clear lack repeating structures)
It was a bit of a fudge when the term "observable universe" was
standardized in reference to the current 13.7 billion light year old universe.

Now that we know about dark energy expansion, however, a new term is clearly needed.
I don't think so. Use whatever term you want. Or, you can use "observable universe" and be understood clearly.
Not to someone struggling to understand why a 13.7 billion year old "observable universe"
can be 90 billion lyr wide when most of it will NEVER EVER be "observable."
Art Neuendorffer

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Re: APOD: Star Size Comparison 2 (2018 Jun 12)

Post by Chris Peterson » Tue Jun 12, 2018 7:02 pm

neufer wrote:
Tue Jun 12, 2018 6:54 pm
Chris Peterson wrote:
Tue Jun 12, 2018 6:37 pm
neufer wrote:
Tue Jun 12, 2018 6:30 pm

Many things about it are known by extrapolation from what is currently observable:
  • 1) its age & size
    2) its composition
    3) its flatness
    4) its general 3D structure (including a clear lack repeating structures)
It was a bit of a fudge when the term "observable universe" was
standardized in reference to the current 13.7 billion light year old universe.

Now that we know about dark energy expansion, however, a new term is clearly needed.
I don't think so. Use whatever term you want. Or, you can use "observable universe" and be understood clearly.
Not to someone struggling to understand why a 13.7 billion year old "observable universe"
can be 90 billion lyr wide when most of it will NEVER EVER be "observable."
That is not such a difficult concept. If can be understood by proper explanation, not by inventing new terms that have no common acceptance.
Chris

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DrJoeS

Re: APOD: Star Size Comparison 2 (2018 Jun 12)

Post by DrJoeS » Tue Jun 12, 2018 7:26 pm

Great video. Enjoyed it all. I cannot comprehend the vastness of space and this make me less likely to. :shock:

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Re: APOD: Star Size Comparison 2 (2018 Jun 12)

Post by ems57fcva » Tue Jun 12, 2018 8:03 pm

G Wolf wrote:
Tue Jun 12, 2018 6:16 pm
Thank you for posting that APOD Team.

This video is a nice addition to the various astronomical size comparison videos I've seen over the years. The addition of the solar system objects direct size comparison is a nice addition. It's the first time I've seen an asteroid included. The only thing I'd add would be Sedna or something else from the Kuyper Belt. Being an English major the only error I noticed was a grammar one. Instead of saying "there are many millions planets" I would have put "there are untold millions of planets." Or was it stars...?
Pluto appears just to the left of the Moon at the start. I fail to see how that does not fulfill your wish to have something from the Kuiper Belt present. And being the largest (known) Kuiper Belt object, that makes it all the more appropriate. Also note that Ceres, the largest member of the asteroid belt, is just to the left of Pluto.

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Re: APOD: Star Size Comparison 2 (2018 Jun 12)

Post by neufer » Tue Jun 12, 2018 9:00 pm

https://en.wikipedia.org/wiki/History_of_geography wrote: <<Thales of Miletus is one of the first known philosophers known to have wondered about the shape of the world. He proposed that the world was based on water, and that all things grew out of it. He also laid down many of the astronomical and mathematical rules that would allow geography to be studied scientifically.

According to the geographer Eratosthenes, Anaximander was the first to publish a map of the [known] world. Anaximander's innovation was to represent the entire inhabited land known to the ancient Greeks. Surely aware of the sea's convexity, he may have designed his map on a slightly rounded metal surface. The centre or “navel” of the world (ὀμφαλός γῆς omphalós gẽs) could have been Delphi, but is more likely in Anaximander's time to have been located near Miletus. The Aegean Sea was near the map's centre and enclosed by three continents, themselves located in the middle of the ocean and isolated like islands by sea and rivers. Europe was bordered on the south by the Mediterranean Sea and was separated from Asia by the Black Sea, the Lake Maeotis, and, further east, either by the Phasis River (now called the Rioni) or the Tanais. The Nile flowed south into the ocean, separating Libya (which was the name for the part of the then-known African continent) from Asia.

Hecataeus of Miletus (Greek: Ἑκαταῖος ὁ Μιλήσιος; c. 550 BC – c. 476 BC) initiated a different form of geography, avoiding the mathematical calculations of Thales and Anaximander he learnt about the world by gathering previous works and speaking to the sailors who came through the busy port of Miletus. From these accounts he wrote a detailed prose account of what was known of the world.>>
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Guest

Re: APOD: Star Size Comparison 2 (2018 Jun 12)

Post by Guest » Tue Jun 12, 2018 11:48 pm

I was amazed by the "Star Size Comparison 2" video! The one thing that came to my mind was that:
if the Earth is so small, would anyone else on a giant sized planet ever know we are here?
Also, would a giant sun have planets with equally giant-sized humanoid lifeforms, on it.
(Like that old TV series, "Land of the Giants", from circa 1970's).
But seriously, would our Earth ever get noticed, amongst such giant-sized exo-planets?

Dr.T

Re: APOD: Star Size Comparison 2 (2018 Jun 12)

Post by Dr.T » Wed Jun 13, 2018 12:27 am

How about including a red dwarf? They are by far the most common star.