2 Questions for Astronomers

Over the years I have heard astronomers repeatedly say two things to
the public so many times that they have become common knowledge. My
studies have led me to believe that these are not actually the facts.
Can somebody straighten me out ?

A) Our sun is just an avergage star.

It seems that the vast, vast majority of stars are class M7 at
most, probably M2 is even more average. Aren't these stars far
enough away from our sun in size and temperature to make the
statement "our sun is average" highly inaccurate ? I am quite
sure that M class stars are the norm in other galaxies as well.

B) The earth will end when the sun burns out, and the orbit of earth
will come close to or be enveloped by the edge of the sun, thereby
burning it out of existence.

The sun will burn out in about 5 to 7 billion years. However,
the probablity is extremely high that the Andromeda
galaxy will hit our galaxy in about 2 to 3 billion years. Every
thing I have seen indicates that this will be a cataclysmic
event. How come astronomers dont say "The earth will surely
end when the Andromeda galaxy collides with the Milky way in a
few billion years, and if that doesn't happen we will have to wait
for the sun to burn out in about 6 billion years"

I have heard astronomers talk about the Andromeda Milky Way
collision, but usually it isn't mentioned when the demise of the
earth is the subject. Shouldn't it be the first thing brought up?

-----
Sorry, my email has been so destroyed by spam I don't even read it
anymore. Please respond here

(BRAINIAC) writes:

Over the years I have heard astronomers repeatedly say two things to
the public so many times that they have become common knowledge. My
studies have led me to believe that these are not actually the facts.
Can somebody straighten me out ?

A) Our sun is just an avergage star.

It seems that the vast, vast majority of stars are class M7 at
most, probably M2 is even more average. Aren't these stars far
enough away from our sun in size and temperature to make the
statement "our sun is average" highly inaccurate ? I am quite
sure that M class stars are the norm in other galaxies as well.

As always, that depends on how one defines "average." Would that be mean,
median or mode? Average radius, average mass, or average luminosity ??
Would that be on a linear scale, or on a logarithmic scale ???
(Astronomers classify stars by their "magnitude," which is a logarithmic
rather than a linear scale.) Or perhaps it could just be a simple as,
"The letter `G' is smack dab in the middle of the spectral sequence:
W, O, B, A, F, G, K, M, N, R, S."


B) The earth will end when the sun burns out, and the orbit of earth
will come close to or be enveloped by the edge of the sun, thereby
burning it out of existence.

The sun will burn out in about 5 to 7 billion years. However,
the probablity is extremely high that the Andromeda
galaxy will hit our galaxy in about 2 to 3 billion years. Every
thing I have seen indicates that this will be a cataclysmic
event.

That depends on how you define "cataclysmic." For example, while the _gas_
in the two galaxies will collide, and possibly lead to a new burst of star
formation, the probability of the Sun colliding with another star during
this process is UTTERLY NEGLIGIBLE, just as it is now, because stars are
so darned far apart; It will go from "almost nothing," to twice "almost
nothing."

Even the probabilitiy of another star passing _close_ enough to the Solar
system to perturb its planetray orbits is quite small; The solar system is
only a light-day or so across, whereas stars are light YEARS apart on the
average. It might pass close enough to dump some comets out of the Oort
shell on us, but almost certainly nothin more severe than that. Likewise,
the odds of the Sun getting ejected out of the galaxy or tossed into the
reactivated core are quite small; only a small fraction of the stars in the
outermost regions of the two galaxies will suffer the former fate (which
wll be essentially harmless, anyway, except the the night sky will have a
lot fewer stars in it), whereas the latter fate is almost certainly rule out
because the Sun has too much orbital angular momentum to wind up on an
"box orbit" or "thin tube orbit." Nor is it likely to get fried should the
gas that gets dumped into the supermassive black holes at the two galaxy's
core cause them to light back up as quasars: We are two far out for that.
Hence, the effects of the "collision" are hardly what one would call "catyclismic!"


How come astronomers dont say "The earth will surely
end when the Andromeda galaxy collides with the Milky way in a
few billion years,

For the reasons I enumerated above --- plus the fact that whether or not
the two galaxies will actually pass close enough to each other to "collide"
someday is hardly 100% certain, even now.

Finally, there is the fact that we now have evidence that the Milky way has
=ALREADY= "canibalized" three galaxies, yet the Earth is still here.


I have heard astronomers talk about the Andromeda Milky Way
collision, but usually it isn't mentioned when the demise of the
earth is the subject. Shouldn't it be the first thing brought up?

No, because:

1.) The "collision" is not a "done deal," yet;

2.) The effects of the "collision" will =NOT= be especially "cataclysmic."


-- Gordon D. Pusch

perl -e '$_ = \n"; s/NO\.//; s/SPAM\.//; print;'

(BRAINIAC) writes:

Over the years I have heard astronomers repeatedly say two things to
the public so many times that they have become common knowledge. My
studies have led me to believe that these are not actually the facts.
Can somebody straighten me out ?

A) Our sun is just an avergage star.

It seems that the vast, vast majority of stars are class M7 at
most, probably M2 is even more average. Aren't these stars far
enough away from our sun in size and temperature to make the
statement "our sun is average" highly inaccurate ? I am quite
sure that M class stars are the norm in other galaxies as well.

As always, that depends on how one defines "average." Would that be mean,
median or mode? Average radius, average mass, or average luminosity ??
Would that be on a linear scale, or on a logarithmic scale ???
(Astronomers classify stars by their "magnitude," which is a logarithmic
rather than a linear scale.) Or perhaps it could just be a simple as,
"The letter `G' is smack dab in the middle of the spectral sequence:
W, O, B, A, F, G, K, M, N, R, S."


B) The earth will end when the sun burns out, and the orbit of earth
will come close to or be enveloped by the edge of the sun, thereby
burning it out of existence.

The sun will burn out in about 5 to 7 billion years. However,
the probablity is extremely high that the Andromeda
galaxy will hit our galaxy in about 2 to 3 billion years. Every
thing I have seen indicates that this will be a cataclysmic
event.

That depends on how you define "cataclysmic." For example, while the _gas_
in the two galaxies will collide, and possibly lead to a new burst of star
formation, the probability of the Sun colliding with another star during
this process is UTTERLY NEGLIGIBLE, just as it is now, because stars are
so darned far apart; It will go from "almost nothing," to twice "almost
nothing."

Even the probabilitiy of another star passing _close_ enough to the Solar
system to perturb its planetray orbits is quite small; The solar system is
only a light-day or so across, whereas stars are light YEARS apart on the
average. It might pass close enough to dump some comets out of the Oort
shell on us, but almost certainly nothin more severe than that. Likewise,
the odds of the Sun getting ejected out of the galaxy or tossed into the
reactivated core are quite small; only a small fraction of the stars in the
outermost regions of the two galaxies will suffer the former fate (which
wll be essentially harmless, anyway, except the the night sky will have a
lot fewer stars in it), whereas the latter fate is almost certainly rule out
because the Sun has too much orbital angular momentum to wind up on an
"box orbit" or "thin tube orbit." Nor is it likely to get fried should the
gas that gets dumped into the supermassive black holes at the two galaxy's
core cause them to light back up as quasars: We are two far out for that.
Hence, the effects of the "collision" are hardly what one would call "catyclismic!"


How come astronomers dont say "The earth will surely
end when the Andromeda galaxy collides with the Milky way in a
few billion years,

For the reasons I enumerated above --- plus the fact that whether or not
the two galaxies will actually pass close enough to each other to "collide"
someday is hardly 100% certain, even now.

Finally, there is the fact that we now have evidence that the Milky way has
=ALREADY= "canibalized" three galaxies, yet the Earth is still here.


I have heard astronomers talk about the Andromeda Milky Way
collision, but usually it isn't mentioned when the demise of the
earth is the subject. Shouldn't it be the first thing brought up?

No, because:

1.) The "collision" is not a "done deal," yet;

2.) The effects of the "collision" will =NOT= be especially "cataclysmic."


-- Gordon D. Pusch

perl -e '$_ = \n"; s/NO\.//; s/SPAM\.//; print;'

In message , BRAINIAC
writes
Over the years I have heard astronomers repeatedly say two things to
the public so many times that they have become common knowledge. My
studies have led me to believe that these are not actually the facts.
Can somebody straighten me out ?

A) Our sun is just an avergage star.

It seems that the vast, vast majority of stars are class M7 at
most, probably M2 is even more average. Aren't these stars far
enough away from our sun in size and temperature to make the
statement "our sun is average" highly inaccurate ? I am quite
sure that M class stars are the norm in other galaxies as well.

Absolutely. In fact the more recent texts take account of observations
of the nearest stars to the Earth and say that our sun is fairly
exceptional.


B) The earth will end when the sun burns out, and the orbit of earth
will come close to or be enveloped by the edge of the sun, thereby
burning it out of existence.

The sun will burn out in about 5 to 7 billion years. However,
the probablity is extremely high that the Andromeda
galaxy will hit our galaxy in about 2 to 3 billion years. Every
thing I have seen indicates that this will be a cataclysmic
event. How come astronomers dont say "The earth will surely
end when the Andromeda galaxy collides with the Milky way in a
few billion years, and if that doesn't happen we will have to wait
for the sun to burn out in about 6 billion years"


I really should check this one, but I'm fairly sure that the collision
with M31 isn't due for perhaps 10 billion years, well after the sun has
become a red giant (assuming we haven't moved the Earth first)
Also, it's not certain that the galaxies will collide, as no-one knows
M31's transverse velocity.
--
"It is written in mathematical language"

In message , BRAINIAC
writes
Over the years I have heard astronomers repeatedly say two things to
the public so many times that they have become common knowledge. My
studies have led me to believe that these are not actually the facts.
Can somebody straighten me out ?

A) Our sun is just an avergage star.

It seems that the vast, vast majority of stars are class M7 at
most, probably M2 is even more average. Aren't these stars far
enough away from our sun in size and temperature to make the
statement "our sun is average" highly inaccurate ? I am quite
sure that M class stars are the norm in other galaxies as well.

Absolutely. In fact the more recent texts take account of observations
of the nearest stars to the Earth and say that our sun is fairly
exceptional.


B) The earth will end when the sun burns out, and the orbit of earth
will come close to or be enveloped by the edge of the sun, thereby
burning it out of existence.

The sun will burn out in about 5 to 7 billion years. However,
the probablity is extremely high that the Andromeda
galaxy will hit our galaxy in about 2 to 3 billion years. Every
thing I have seen indicates that this will be a cataclysmic
event. How come astronomers dont say "The earth will surely
end when the Andromeda galaxy collides with the Milky way in a
few billion years, and if that doesn't happen we will have to wait
for the sun to burn out in about 6 billion years"


I really should check this one, but I'm fairly sure that the collision
with M31 isn't due for perhaps 10 billion years, well after the sun has
become a red giant (assuming we haven't moved the Earth first)
Also, it's not certain that the galaxies will collide, as no-one knows
M31's transverse velocity.
--
"It is written in mathematical language"

In article ,
Jonathan Silverlight writes:
Absolutely. In fact the more recent texts take account of observations
of the nearest stars to the Earth and say that our sun is fairly
exceptional.

Some trivia questions:

1. What's the nearest star that is more luminous than the Sun, and
how far away is it?

2. How many stellar systems are nearer than the star in question 1?

--
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA
(Please email your reply if you want to be sure I see it; include a
valid Reply-To address to receive an acknowledgement. Commercial
email may be sent to your ISP.)

In article ,
Jonathan Silverlight writes:
Absolutely. In fact the more recent texts take account of observations
of the nearest stars to the Earth and say that our sun is fairly
exceptional.

Some trivia questions:

1. What's the nearest star that is more luminous than the Sun, and
how far away is it?

2. How many stellar systems are nearer than the star in question 1?

--
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA
(Please email your reply if you want to be sure I see it; include a
valid Reply-To address to receive an acknowledgement. Commercial
email may be sent to your ISP.)

In article ,
(Steve Willner) writes:
Some trivia questions:

1. What's the nearest star that is more luminous than the Sun, and
how far away is it?

That one turned out to be more trivial than I expected. As Bill
pointed out, alpha Cen A is the answer. Somehow I had the mistaken
impression that it is fainter than the Sun, but in fact it's half a
magnitude brighter (in V).

Bill also pointed out (in private correspondence, quoted by
permission) that Sirius (2.64 pc) is the 6th closest star and 4th
closest system, and Procyon (3.50 pc) is the 12th closest star. I
had a look at the table of 100 nearest stars (not systems) in
_Allen's Astrophysical Quantities_ and found two A stars (Sirius and
Altair at 5.1 pc), one F star (Procyon), and nine of type G. (I
don't promise not to have missed any!) All the rest are of fainter
types. The most distant star in the list is at 7.6 pc. The
early-type stars seem unexpectedly close to the Sun, but that's
probably just statistics of small numbers. In absolute V magnitude,
four of the nine G stars are brighter than the Sun, so it's about
average for a G star. All in all, it seems fair to say the Sun is
rather brighter than an average star but not so bright as to be
considered a rare type.

Bill also writes:
If I remember my Galactic astronomy course, the frequency of G or
earlier should be quite a bit less than 12%. Hmmm ... I'm looking
at my 2nd edition Mihalas & Binney ... looks like there are about
6000 stars / 10^6 pc^3 brighter than the sun, or one per 170 pc^3.
You're counting 12 in a volume of 1840 pc^3, or one per 150 pc^3.
That doesn't strike me as too very different.

I've learned a few things. Thanks to all who responded, especially
Bill.

--
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA
(Please email your reply if you want to be sure I see it; include a
valid Reply-To address to receive an acknowledgement. Commercial
email may be sent to your ISP.)

In article ,
(Steve Willner) writes:
Some trivia questions:

1. What's the nearest star that is more luminous than the Sun, and
how far away is it?

That one turned out to be more trivial than I expected. As Bill
pointed out, alpha Cen A is the answer. Somehow I had the mistaken
impression that it is fainter than the Sun, but in fact it's half a
magnitude brighter (in V).

Bill also pointed out (in private correspondence, quoted by
permission) that Sirius (2.64 pc) is the 6th closest star and 4th
closest system, and Procyon (3.50 pc) is the 12th closest star. I
had a look at the table of 100 nearest stars (not systems) in
_Allen's Astrophysical Quantities_ and found two A stars (Sirius and
Altair at 5.1 pc), one F star (Procyon), and nine of type G. (I
don't promise not to have missed any!) All the rest are of fainter
types. The most distant star in the list is at 7.6 pc. The
early-type stars seem unexpectedly close to the Sun, but that's
probably just statistics of small numbers. In absolute V magnitude,
four of the nine G stars are brighter than the Sun, so it's about
average for a G star. All in all, it seems fair to say the Sun is
rather brighter than an average star but not so bright as to be
considered a rare type.

Bill also writes:
If I remember my Galactic astronomy course, the frequency of G or
earlier should be quite a bit less than 12%. Hmmm ... I'm looking
at my 2nd edition Mihalas & Binney ... looks like there are about
6000 stars / 10^6 pc^3 brighter than the sun, or one per 170 pc^3.
You're counting 12 in a volume of 1840 pc^3, or one per 150 pc^3.
That doesn't strike me as too very different.

I've learned a few things. Thanks to all who responded, especially
Bill.

--
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA
(Please email your reply if you want to be sure I see it; include a
valid Reply-To address to receive an acknowledgement. Commercial
email may be sent to your ISP.)

In message , Roger Stokes
writes
"BRAINIAC" wrote in message
...
A) Our sun is just an avergage star.

There are 71 stars within 20 light years of the solar system, of which only
4
(Alpha Centauri A, Sirius, Procyon, and Altair) are brighter than the sun.
Most are M dwarfs. Here's the list (from the hipparcos catalog)

TYPE DISTANCE (LY) MAGNITUDE Name
HIP70890 M5Ve 4.2 +/- 0.00 11.0 Alpha Centauri C (Proxima)
HD128621 K1V 4.4 +/- 0.00 1.4 Alpha Centauri B
HD128620 G2V 4.4 +/- 0.01 -0.0 Alpha Centauri A (Rigil Kent)
HIP87937 sdM4 6.0 +/- 0.04 9.5 Barnard's star

Isn't one of the better-known ones missing from that list?
Wolf 359 was a TV star about 20 years before it featured in "Star Trek:
TNG" (It's the title of an "Outer Limits" story)
--
"It is written in mathematical language"