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Crimson
2004-Aug-28, 02:16 PM
Some "facts" in astronomy are gotten wrong more often than right:

1. "The Sun is an average star." No, it outshines over 95 percent of the stars in the universe.

2. "Delta Cephei was the first Cepheid discovered." No, Eta Aquilae was.

3. "Uranus and Neptune are gas giants." No, in our solar system, only Jupiter and Saturn are, for only they consist mostly of hydrogen and helium.

4. "Percival Lowell predicted a ninth planet's existence by studying irregularities in the orbital motion of Neptune." No, he used Uranus.

5. "The Milky Way is an average galaxy." No, it's far larger and brighter than most galaxies in the universe.

6. "Edwin Hubble discovered that most galaxies have redshifts and are moving away from us." No, Vesto Slipher did.

Glom
2004-Aug-28, 02:54 PM
You've broken our hearts. [-(

earthman2110
2004-Aug-28, 03:49 PM
I agree with all of those except for the first one. I'm pretty sure that our sun is right in the middle, between the brightest and the faintest stars, so I suppose that would make our sun the median? But like you said, it outshines most other stars, because there are many more faint stars than there are bright ones. Hm... I guess you were right. thank you

Crimson
2004-Aug-28, 05:12 PM
You've broken our hearts. [-(

Cheer up! You orbit a star that ranks in the top 5 percent of all stars in the Galaxy. And that galaxy itself ranks in the top 5 percent of all galaxies in the universe.

umop ap!sdn
2004-Aug-28, 05:18 PM
3. "Uranus and Neptune are gas giants." No, in our solar system, only Jupiter and Saturn are, for only they consist mostly of hydrogen and helium.

Then what are Uranus and Neptune? :-k

Brady Yoon
2004-Aug-28, 05:28 PM
3. "Uranus and Neptune are gas giants." No, in our solar system, only Jupiter and Saturn are, for only they consist mostly of hydrogen and helium.

That's just like saying, Mars is not a terrestrial planet. It has a slightly lower content of iron than Mercury, Venus, and Earth. Neptune and Uranus both are composed mainly of hydrogen and helium. Uranus and Neptune are composed of about 85% hydrogen and 5 % helium with small amounts of methane and ammonia. This is very similar to the atmospheres of Jupiter and Saturn.

But there is a difference between the larger and smaller gas giants. Jupiter and Saturn have mostly metallic/liquid hydrogen because of their greater mass, and Uranus and Neptune have mostly gaseous hydrogen.

Crimson
2004-Aug-28, 06:11 PM
Actually, although Jupiter, Saturn, Uranus, and Neptune are all giant planets, only Jupiter and Saturn are gas giants. They are predominantly hydrogen and helium. In contrast, Uranus and Neptune are mostly rock and water, topped by thick hydrogen-helium atmospheres that constitute just a fraction of their mass.

Crimson
2004-Aug-28, 06:33 PM
Then what are Uranus and Neptune? :-k

Some scientists refer to Uranus and Neptune as ice giants (http://www.spacedaily.com/news/uranus-99c.html), but I think this terminology is misleading.

Lurker
2004-Aug-29, 12:23 AM
Then what are Uranus and Neptune? :-k

Some scientists refer to Uranus and Neptune as ice giants (http://www.spacedaily.com/news/uranus-99c.html), but I think this terminology is misleading.
I'm not sure I understand the problem here... you may or may not be right on these six examples, but science never closes the books on these matters. The proof of that is in the on going discussion and examination of the evidence. Science does its best to piece together the information available. When more evidence is found, the questions are reexamined. It seems to me that your post is proof if this fact. The scientific process in proceeding exactly as it should.

dvb
2004-Aug-29, 12:45 AM
Some "facts" in astronomy are gotten wrong more often than right:

1. "The Sun is an average star." No, it outshines over 95 percent of the stars in the universe.

What's your definition of "average"? I always thought that our sun outshines the rest of the stars because it's closer to us. Much like a light bulb would appear brighter the closer you are to it.

Am I right?

Am I right? :D

Lurker
2004-Aug-29, 12:50 AM
Some "facts" in astronomy are gotten wrong more often than right:

1. "The Sun is an average star." No, it outshines over 95 percent of the stars in the universe.

What's your definition of "average"? I always thought that our sun outshines the rest of the stars because it's closer to us. Much like a light bulb would appear brighter the closer you are to it.

Am I right?

Am I right? :D
Now don' you be makin me tak u out ta da woodshed youngun!! :wink:

dvb
2004-Aug-29, 01:00 AM
Some "facts" in astronomy are gotten wrong more often than right:

1. "The Sun is an average star." No, it outshines over 95 percent of the stars in the universe.

What's your definition of "average"? I always thought that our sun outshines the rest of the stars because it's closer to us. Much like a light bulb would appear brighter the closer you are to it.

Am I right?

Am I right? :D
Now don' you be makin me tak u out ta da woodshed youngun!! :wink:

(runs and hides) 8-[

dgruss23
2004-Aug-29, 01:26 AM
I agree with all of those except for the first one. I'm pretty sure that our sun is right in the middle, between the brightest and the faintest stars, so I suppose that would make our sun the median? But like you said, it outshines most other stars, because there are many more faint stars than there are bright ones. Hm... I guess you were right. thank you

This is a confusing concept for many. I often do a lab that nicely illustrates it with my students. The Sun is kind of average in terms of the range of possible sizes and luminosities. However, in terms of the population of stars in the galaxy, Crimson is correct that about 90-95% of the stars are actually smaller than the Sun.

Crimson
2004-Aug-29, 01:50 AM
Being in the middle of a range does not make you average. Suppose, for example, that you take a test on which possible scores range from 0 to 100. You get a 50--exactly the middle of the range. Are you average? Answer: it depends on the scores that others got. If everyone else got a 25, then you're far above average; but if everyone else got a 90, you're in trouble.

The Sun's luminosity places it in the middle of the range from the most luminous stars to the least luminous stars. But this does NOT make it average, because over 95 percent of all stars are less luminous than the Sun.

If you took the one hundred nearest individual stars (http://www.chara.gsu.edu/RECONS/TOP100.htm) and placed them at the same distance from us as the Sun, only four would look brighter than the Sun: Alpha Centauri A, Sirius A, Procyon A, and Altair. All the rest would look fainter.

The average star is a red dwarf.

dvb
2004-Aug-29, 03:30 AM
Being in the middle of a range does not make you average. Suppose, for example, that you take a test on which possible scores range from 0 to 100. You get a 50--exactly the middle of the range. Are you average? Answer: it depends on the scores that others got. If everyone else got a 25, then you're far above average; but if everyone else got a 90, you're in trouble.

The Sun's luminosity places it in the middle of the range from the most luminous stars to the least luminous stars. But this does NOT make it average, because over 95 percent of all stars are less luminous than the Sun.

If you took the one hundred nearest individual stars (http://www.chara.gsu.edu/RECONS/TOP100.htm) and placed them at the same distance from us as the Sun, only four would look brighter than the Sun: Alpha Centauri A, Sirius A, Procyon A, and Altair. All the rest would look fainter.

The average star is a red dwarf.

Ahh! The definition of average wasn't explained very well in your original post. Thanks for your explanation, I understand now. :)

So you're talking the entire universe, or just our galaxy?

We can interpret statistics many different ways. We have mean, median, and mode for interpreting different types of averages.

beskeptical
2004-Aug-29, 07:13 AM
You've broken our hearts. [-(

Cheer up! You orbit a star that ranks in the top 5 percent of all stars in the Galaxy. And that galaxy itself ranks in the top 5 percent of all galaxies in the universe.Wrong! Since we can only see the galaxies that are near enough for their light to have reached us, we can't make any claims about "all galaxies in the universe". And Universe should be capitalized. :wink: :wink:

Actually, I'm glad you cleared the other stuff up. I hate having my facts wrong. :D

dgruss23
2004-Aug-29, 01:12 PM
Crimson: 5. "The Milky Way is an average galaxy." No, it's far larger and brighter than most galaxies in the universe.

This is also true because by far most galaxies are dwarfs. Even in our Local Group we see it. M-31, the Milky Way, and M-33 are the 3 biggest galaxies.

In terms of spiral galaxies however, the Milky Way really is truly average.

MrObvious
2004-Aug-30, 05:34 AM
Brady Yoon wrote:

But there is a difference between the larger and smaller gas giants. Jupiter and Saturn have mostly metallic/liquid hydrogen because of their greater mass, and Uranus and Neptune have mostly gaseous hydrogen.


Then Uranus and Neptune really are the gas giants and Jupiter and Saturn should be the liquid giants 8-[

Kaptain K
2004-Aug-30, 09:23 AM
I know there are dwarf ellipticals and dwarf irregulars. Are there any dwarf spirals? :o

George
2004-Aug-30, 01:53 PM
I know there are dwarf ellipticals and dwarf irregulars. Are there any dwarf spirals? :o
Apparently yes.... dwarf spiral (http://zebu.uoregon.edu/~js/dS/comparison.html).

George
2004-Aug-30, 01:58 PM
It seems dwarf spirals are something new, however.

Article in May 2000...

But one thing that had never been seen was a dwarf spiral galaxy, until now...
[added]...Astronomers are unsure what caused the spiral structure, but said it implies IC 3382 harbors a thin disk of gas, dust and stars. The disk may have been created by the gravitational interaction with two nearby dwarf galaxies
From.... here (http://www.space.com/scienceastronomy/astronomy/virgo_dwarf_000517.html)

Russ
2004-Aug-30, 02:21 PM
Some "facts" in astronomy are gotten wrong more often than right:

3. "Uranus and Neptune are gas giants." No, in our solar system, only Jupiter and Saturn are, for only they consist mostly of hydrogen and helium.


I have read Astronomy, Sky & Telescope and Scientific American EVERY month for a very long time. I estimate 30 years. My memory map tells me that I have read many articles that refered to both Uranus and Neptune as gas giants. Nevery one saying they were not.

Would you please cite a credible source that supports your position by saying that they are not gas giants? I'll grant you the possibility this is true but would like to see the words from a credible source. . :D 8)

(edit to correct same dumb typo twice)

Ut
2004-Aug-30, 02:37 PM
Being in the middle of a range does not make you average. Suppose, for example, that you take a test on which possible scores range from 0 to 100. You get a 50--exactly the middle of the range. Are you average? Answer: it depends on the scores that others got.

It also depends on the kind of average you're taking. The sun isn't an average star if you take the mean or mode average, but it is if you take the median average.


I recall hearing that Uranus and Neptune consist largely of a water and amonia ice slurry, with thick atmospheres of helium and methane. That was years ago, though (I guess it's time to buy some new books on the solar system -- I'm way behind in my reading).

At the same time, I also recall hearing that Jupiter and Saturn consist largely of liquid and metallic hydrogen, with thick atmospheres of hydrogen and helium. So, none of the giant planets are made of mostly gas. If you're going to eliminate the smaller two, then I don't see any reason to eliminate the larger two. None of them are gas giants.

I think an important distinction has been lost here: The difference between a Jovian planet and other types of giant planets. There's no reason for every gas giant to be a Jovian planet...

dgruss23
2004-Aug-30, 02:56 PM
I know there are dwarf ellipticals and dwarf irregulars. Are there any dwarf spirals? :o

There has only been a few reports of dwarf spirals as noted above. Here (http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995AJ....110.2067S&db_key=A ST&high=3e5c03c80a23405) was the first study that found evidence for such dwarfs.

Crimson
2004-Aug-30, 05:53 PM
I have read Astronomy, Sky & Telescope and Scientific American EVERY month for a very long time. I estimate 30 years. My memory map tells me that I have read many articles that refered to both Uranus and Neptune as gas giants. Nevery one saying they were not.

Would you please cite a credible source that supports your position by saying that they are not gas giants? I'll grant you the possibility this is true but would like to see the words from a credible source. . :D 8)


Online: here (http://www.spacedaily.com/news/uranus-99c.html).

Magazine: Sky and Telescope, April 2000, page 24: "Uranus and Neptune have long posed a problem to solar-system theorists. The two `ice-giant' planets shouldn't exist--not if they formed in their present locations."

Book: Planet Quest (http://KenCroswell.com/planetquest.html) by Ken Croswell, glossary definition of "gas giant": "Gas Giant. A planet consisting mostly of hydrogen and helium. Our solar system has two gas giants: Jupiter and Saturn. Uranus and Neptune are sometimes erroneously called gas giants, too, but they are not, since the hydrogen and helium constitute only a fraction of the planets' mass."

Crimson
2004-Aug-30, 06:07 PM
Being in the middle of a range does not make you average. Suppose, for example, that you take a test on which possible scores range from 0 to 100. You get a 50--exactly the middle of the range. Are you average? Answer: it depends on the scores that others got.

It also depends on the kind of average you're taking. The sun isn't an average star if you take the mean or mode average, but it is if you take the median average.

Average means mean, but even if you use the mode or the median, the Sun's absolute magnitude ranks far above those of its peers. Median simply means the absolute magnitude where 50 percent of stars are brighter and 50 percent of stars are fainter. The Sun's luminosity is well above the median. The Sun's absolute magnitude is +4.83, whereas the median absolute magnitude is in the teens. (Note: the lower the absolute magnitude, the brighter the star.)


I recall hearing that Uranus and Neptune consist largely of a water and amonia ice slurry, with thick atmospheres of helium and methane. That was years ago, though (I guess it's time to buy some new books on the solar system -- I'm way behind in my reading).

At the same time, I also recall hearing that Jupiter and Saturn consist largely of liquid and metallic hydrogen, with thick atmospheres of hydrogen and helium. So, none of the giant planets are made of mostly gas. If you're going to eliminate the smaller two, then I don't see any reason to eliminate the larger two. None of them are gas giants.

Jupiter and Saturn are called gas giants because they're made mostly of hydrogen and helium, which on Earth are gases. On Jupiter and Saturn, as you point out, the hydrogen is mostly not gaseous.

Uranus and Neptune should not be called gas giants because they don't consist mostly of hydrogen and helium.

CJSF
2004-Aug-30, 07:35 PM
I always presumed the term gas giant meant the planets were 1. Huge compared to Earth, and 2. had large volume atmospheres. Aren't Uranus' and Neptune's atmospheres huge comprted to the radii of the whole planet?

I found this page (http://www.mhhe.com/physsci/astronomy/arny/instructor/graphics/ch09/0919.html) that seems to show that a HUGE part of Uranus' total visible volume is hydrogen gas.

CJSF

um3k
2004-Aug-30, 08:28 PM
If they do not consist mostly of hydrogen and helium, then shouldn't they be metal giants?

:lol:

Crimson
2004-Aug-30, 08:29 PM
The hydrogen and helium account for only about 10 percent of the mass of Uranus and Neptune, whereas they account for most of the mass of Jupiter and Saturn.

logicboy
2004-Aug-30, 08:57 PM
If they do not consist mostly of hydrogen and helium, then shouldn't they be metal giants?

:lol:

Wouldn't Metallica, Pantera, Alice Cooper etc. fall into the Metal Giant category as well?

:P

I just had to say it

TriangleMan
2004-Aug-31, 10:57 AM
4. "Percival Lowell predicted a ninth planet's existence by studying irregularities in the orbital motion of Neptune." No, he used Uranus.


This space.com article (http://www.space.com/reference/pluto/history.html) says he used Neptune. What is your source that he used Uranus?

(edited to add: found a website (http://www.physics.gmu.edu/classinfo/astr103/CourseNotes/ECText/Bios/lowell.htm) that says he used Uranus, so which version is right?)

Crimson
2004-Aug-31, 01:58 PM
Lowell used Uranus.

William Graves Hoyt, in his book Planets X and Pluto (http://www.amazon.com/exec/obidos/ASIN/0816506841), page 108, quotes Lowell: "`We cannot use Neptune as a finger-post to a trans-Neptunian [planet] as Uranus was used for Neptune because we do not possess observations of Neptune far enough back,' Lowell pointed out in his memoir. `A disturbed body must have pursued a fairly long path before the effects of perturbation detach themselves from what may well be represented by altering the elements of the disturbed. Neptune has not been known long enough to do this.'"

Ken Croswell, in his book Planet Quest (http://KenCroswell.com/planetquest.html), pages 48-49: "Lowell tried to predict the [ninth] planet's location, as Adams and Leverrier had Neptune's, by examining irregularities in the motion of Uranus. However, the task was far worse than the one that had faced Adams and Leverrier. The irregularities in Uranus's motion were much smaller than those which Adams and Leverrier had used. In addition, for Adams and Leverrier, Neptune had been the solution; for Lowell, it was part of the problem. Not only did Neptune perturb Uranus, but Neptune's orbit was not well determined, because the planet takes 165 years to revolve and had not yet been observed over a full cycle. Therefore, Lowell could not know whether Neptune was following its proper path. This forced Lowell to use only Uranus."

TriangleMan
2004-Aug-31, 05:11 PM
Thanks Crimson, I always thought it was irregularities with Neptune that was used to try to find PX/Pluto.

Russ
2004-Aug-31, 09:20 PM
Online: here (http://www.spacedaily.com/news/uranus-99c.html).

Magazine: Sky and Telescope, April 2000, page 24: "Uranus and Neptune have long posed a problem to solar-system theorists. The two `ice-giant' planets shouldn't exist--not if they formed in their present locations."

Book: Planet Quest (http://KenCroswell.com/planetquest.html) by Ken Croswell, glossary definition of "gas giant": "Gas Giant. A planet consisting mostly of hydrogen and helium. Our solar system has two gas giants: Jupiter and Saturn. Uranus and Neptune are sometimes erroneously called gas giants, too, but they are not, since the hydrogen and helium constitute only a fraction of the planets' mass."

Hmmmmmm. Very interesting. I will have to research this more. Thank you. 8)

Russ
2004-Sep-03, 05:31 AM
Online: here (http://www.spacedaily.com/news/uranus-99c.html).

Magazine: Sky and Telescope, April 2000, page 24: "Uranus and Neptune have long posed a problem to solar-system theorists. The two `ice-giant' planets shouldn't exist--not if they formed in their present locations."

Book: Planet Quest (http://KenCroswell.com/planetquest.html) by Ken Croswell, glossary definition of "gas giant": "Gas Giant. A planet consisting mostly of hydrogen and helium. Our solar system has two gas giants: Jupiter and Saturn. Uranus and Neptune are sometimes erroneously called gas giants, too, but they are not, since the hydrogen and helium constitute only a fraction of the planets' mass."

I was able to take some time today and do a fair amount of research on your claim that Uranus and Neptune are not gas giants. Except for your two citations, I couldn't find any other statement or implication that they were not gas giants.

Is it possible that this is another terminology war similar to the planetary status of Pluto? :) :wink:

Chip
2004-Sep-03, 10:03 AM
1. "The Sun is an average star." No, it outshines over 95 percent of the stars in the universe.

Do you mean as seen from Earth? The 5% would include supernovas?

2. "Delta Cephei was the first Cepheid discovered." No, Eta Aquilae was.

The name "Cepheid" by the way is from the constellation Cepheus.

3. "Uranus and Neptune are gas giants." No, in our solar system, only Jupiter and Saturn are, for only they consist mostly of hydrogen and helium.

The term "gas giant" was invented by science fiction writer James Blish, and has since found its way into astronomy. Originally it meant any large planet with a gaseous atmosphere and without a rocky solid surface. The term has since come under the hydrogen and helium description you've listed. However, it is likely that Jupiter also has a large solid core, with much liquid hydrogen and deeper inside, metallic hydrogen, so "gas giant" isn't quite accurate - but I'm not quibbling, the term is cool with me. :wink:

4. "Percival Lowell predicted a ninth planet's existence by studying irregularities in the orbital motion of Neptune." No, he used Uranus.

Yeah, I've always read it was the eccentricities of Uranus's orbit that lead Lowell to predict the 9th planet, which Clyde Tombaugh later discovered.

5. "The Milky Way is an average galaxy." No, it's far larger and brighter than most galaxies in the universe.

True, the Milky Way is a giant among galaxies. The statement is rather sweeping however given the size of the universe and the number of galaxies in it, many of which we haven't seen. Of the Local Group, the Andromeda galaxy has approximately twice the mass of the Milky Way, and there are galaxies that are as large, but very far away. The statement: "the Milky Way is an average galaxy" might also lead people to believe that there are identical spirals just like the Milky Way, but even though there are distinct types of galaxies, they are akin to snowflakes. No two alike.

6. "Edwin Hubble discovered that most galaxies have redshifts and are moving away from us." No, Vesto Slipher did.

Yes. The statement probably came about because Hubble also has a lot to do with redshifts and the expansion of the universe.

junkyardfrog
2004-Sep-03, 04:35 PM
Magazine: Sky and Telescope, April 2000, page 24: "Uranus and Neptune have long posed a problem to solar-system theorists. The two `ice-giant' planets shouldn't exist--not if they formed in their present locations."


Now that is a fascinating quote! I never heard that before....

Where are they assumed to have formed? Are they assumed to be captured planets?

junkyardfrog
2004-Sep-03, 04:37 PM
hmmm

Why the font change?

TrAI
2004-Sep-03, 11:47 PM
Being in the middle of a range does not make you average. Suppose, for example, that you take a test on which possible scores range from 0 to 100. You get a 50--exactly the middle of the range. Are you average? Answer: it depends on the scores that others got. If everyone else got a 25, then you're far above average; but if everyone else got a 90, you're in trouble.

The Sun's luminosity places it in the middle of the range from the most luminous stars to the least luminous stars. But this does NOT make it average, because over 95 percent of all stars are less luminous than the Sun.

If you took the one hundred nearest individual stars (http://www.chara.gsu.edu/RECONS/TOP100.htm) and placed them at the same distance from us as the Sun, only four would look brighter than the Sun: Alpha Centauri A, Sirius A, Procyon A, and Altair. All the rest would look fainter.

The average star is a red dwarf.

Hmmm... That is interesting. But how would the sun rank in relation to the average in mass distribution?
By this I am thinking that using a size average might be a bit like comparing two heaps of rocks(one with 10 big rocks, and one with 1000 small rocks) and saying that you have a much higher frequency of small rocks, it is perfectly correct, but if you are going to build something from the rocks the mass of the heaps might be a nice thing to know...

I would also think that the older a universe gets, the distribution would move more over to smaller stars..

ritko1
2004-Sep-04, 07:39 AM
It was my understanding that when the sun was refered to an average star, it was done so in it class. As opposed to those in the Supergiant status or Brown Dawf Status. Would it no longer be an average star if you did not include other stars that don't evolve along the same lines? Such as if you only included Yellow Dwarf, Main Sequence Stars?

Grand Vizier
2004-Sep-04, 07:34 PM
New one for your list, which came up on another thread. 'The HST was the first space-based telescope' - or similar wording. New Scientist keeps repeating that one, but I've seen it many times elsewhere.

Plain wrong. As another poster has pointed out, the honour of first space-based astronomical telescope goes to OAO-2 in 1968, though I think if it's worded sloppily (as above), you could go back further and include non-astronomical scopes on reconsats, for example.

Crimson
2004-Sep-04, 07:47 PM
1. "The Sun is an average star." No, it outshines over 95 percent of the stars in the universe.

Do you mean as seen from Earth? The 5% would include supernovas?

No, I mean by luminosity--i.e., intrinsic brightness, or absolute magnitude.


2. "Delta Cephei was the first Cepheid discovered." No, Eta Aquilae was.

The name "Cepheid" by the way is from the constellation Cepheus.

Yes, which misleads many into thinking that Delta Cephei was discovered first. A Google search on "first cepheid" and "delta cephei" returns more pages than does one on "first cepheid" and "eta aquilae."


5. "The Milky Way is an average galaxy." No, it's far larger and brighter than most galaxies in the universe.

True, the Milky Way is a giant among galaxies. The statement is rather sweeping however given the size of the universe and the number of galaxies in it, many of which we haven't seen.

But the ones we haven't seen are almost all less luminous than the Milky Way. Galaxies as luminous as the Milky Way are easy to see. It is also true, as you say, that Andromeda is even bigger than the Milky Way. Andromeda is really a remarkable galaxy.

Crimson
2004-Sep-04, 08:04 PM
Being in the middle of a range does not make you average. Suppose, for example, that you take a test on which possible scores range from 0 to 100. You get a 50--exactly the middle of the range. Are you average? Answer: it depends on the scores that others got. If everyone else got a 25, then you're far above average; but if everyone else got a 90, you're in trouble.

The Sun's luminosity places it in the middle of the range from the most luminous stars to the least luminous stars. But this does NOT make it average, because over 95 percent of all stars are less luminous than the Sun.

If you took the one hundred nearest individual stars (http://www.chara.gsu.edu/RECONS/TOP100.htm) and placed them at the same distance from us as the Sun, only four would look brighter than the Sun: Alpha Centauri A, Sirius A, Procyon A, and Altair. All the rest would look fainter.

The average star is a red dwarf.

Hmmm... That is interesting. But how would the sun rank in relation to the average in mass distribution?

Nearly the same. Most stars are on the main sequence, and for main-sequence stars, there's a correlation between mass and luminosity. The only stars that are substantially fainter than the Sun but more massive would be a few white dwarfs. However, the average white dwarf has a mass of 0.55 to 0.60 solar masses.


By this I am thinking that using a size average might be a bit like comparing two heaps of rocks(one with 10 big rocks, and one with 1000 small rocks) and saying that you have a much higher frequency of small rocks, it is perfectly correct, but if you are going to build something from the rocks the mass of the heaps might be a nice thing to know...

Yes. The only thing I have immediately at hand to answer this question is over 20 years old, page 222 of
Galactic Astronomy (http://www.amazon.com/exec/obidos/ASIN/0716712806) by Dimitri Mihalas and James Binney. The last column of the table on that page gives the contribution, by mass, of stars of different luminosities. According to that table, stars less luminous than the Sun contribute most of the mass of the Galaxy. Massive stars are so rare that they contribute little mass to the Galaxy.

On the other hand, the same table reveals that the light of the Galaxy comes almost entirely from stars more luminous than the Sun. As a result, if you go out at night and point at a random star, it will almost certainly be more luminous than the Sun--even though over 95 percent of all stars are less luminous than the Sun. The moral: looks can be misleading, especially in astronomy.


I would also think that the older a universe gets, the distribution would move more over to smaller stars..

Yes.

Crimson
2004-Sep-04, 08:08 PM
It was my understanding that when the sun was refered to an average star, it was done so in it class. As opposed to those in the Supergiant status or Brown Dawf Status. Would it no longer be an average star if you did not include other stars that don't evolve along the same lines? Such as if you only included Yellow Dwarf, Main Sequence Stars?

Every time I've seen the Sun claimed to be an average star, it's almost always a statement referring to all stars. Keep in mind that yellow main-sequence stars like the Sun make up only 4 percent of all stars in the Milky Way. 80 percent of all stars are red dwarfs. They are the average stars of the universe.

Grand Vizier
2004-Sep-04, 08:25 PM
It was my understanding that when the sun was refered to an average star, it was done so in it class. As opposed to those in the Supergiant status or Brown Dawf Status. Would it no longer be an average star if you did not include other stars that don't evolve along the same lines? Such as if you only included Yellow Dwarf, Main Sequence Stars?

Every time I've seen the Sun claimed to be an average star, it's almost always a statement referring to all stars. Keep in mind that yellow main-sequence stars like the Sun make up only 4 percent of all stars in the Milky Way. 80 percent of all stars are red dwarfs. They are the average stars of the universe.

I have an old astrophysics text going back to the 1960s that states that K-type dwarfs were the most abundant stars. I think that's simply because more Ks were assigned catalogue numbers than Ms at the time. So, by that process, maybe brown dwarfs (if we're counting them as stars) are the most abundant, and we've only catalogued a very few...