If You are an Active Observer, How Many Bolides do You See Annually?

In article ,
says...

On Sun, 17 Feb 2013 07:54:46 +0100, Paul Schlyter
wrote:

That's the definition of bolide too: a meteor brighter than Venus.

No, it isn't. It is one definition, used by somebody (?), and without
any formal basis. Even in discussing meteors, it means different
things to different people.

I'm not saying that there's anything inherently wrong with words that
lack formal definition within any particular professional community,
but where formal definitions exist, it's usually preferable to use
them. "Bolide" is avoided by many in the meteor research community
precisely because of the confusion around exactly how to interpret it.
"Fireball" is perfectly clear.

I think we can find other uses of "fireball" as well, particularly by
non-astronomers...

Of course. But when used in an astronomical context, it is clearly
defined. That's generally a good thing.

Unfortunately, that single formal definition of "fireball" does not
exist. The IAU defines fireball as "a meteor brighter than any of the
planets", i.e. brighter than magnitude -4 as you earlier pointed out.

However, the IMO (International Meteor Organization, an amateur
organization of meteor observers which I'm positive observe meteors
visually much more often than professional astronomers do) uses a
different definition: a fireball is a meteor of magnitude -3 or brighter
if observed at zenith.

The IAU definition is less satisfactory, since the same meteor can be a
"fireball" to one observer nearby but a "non-fireball" to another
observer farther away. The IMO definition removes that inherent
subjectivity in the definition of "fireball".

Numerous fireballs according to the IMO definition will be non-fireballs
according to the IAU definition, not only because the IAU definition uses
a brigter lower limit, but also because the IAU definition lacks the
zenith correction of the meteor's brightness.


Finally, a "bolide" is a particularly bright fireball. When used in an
astronomical context, it's common to put a lower brightness limit at
magnitude -14.


So I was wrong when I considered "bolide" to be synonymous to "fireball".
But I think we can disregard how geologists and other non-astronomers
define "bolide" and "fireball".

On Sun, 17 Feb 2013 19:17:37 +0100, Paul Schlyter
wrote:

The IAU definition is less satisfactory, since the same meteor can be a
"fireball" to one observer nearby but a "non-fireball" to another
observer farther away. The IMO definition removes that inherent
subjectivity in the definition of "fireball".

I agree that the IMO definition is better. In practice, however, I
don't know any IMO members who use it. Almost everybody sticks with
the IAU value of -4, although correction for zenith angle is common.
People seldom worry about the exact magnitude at the low end and
simply refer to any meteor that is observed to be brighter than
_about_ magnitude -4 somewhere along its ground path as a "fireball".
That's because any brightness chosen is arbitrary. At very roughly mag
-4, we are dealing with meteors that have a significant potential for
producing meteorites, hence the distinction.

In fact, the IAU (Commission 22) is currently reviewing the
terminology associated with meteors and meteorites, and it will
probably be changed. AFAIK, however, there is no intent to create a
definition for "bolide", so presumably that term will continue to be
avoided by most researchers.

In sci.astro.amateur message
t, Sun, 17 Feb 2013 07:54:46, Paul Schlyter posted:

On Sat, 16 Feb 2013 17:36:04 -0700, Chris L Peterson
wrote:
On Sat, 16 Feb 2013 22:11:54 +0100, Paul Schlyter
wrote:

What's thé formal definition of fireball??

The IAU formally defines a fireball as any meteor brighter than the
brightest planet, which is generally taken as magnitude -4.

That's the definition of bolide too: a meteor brighter than Venus.

"Bolide" is sometimes used by astronomers in reference to a fireball
that is observed to break up, and it is used by geologists in
reference to a crater forming object.

I think we can find other uses of "fireball" as well, particularly by
non-astronomers...

Does the IAU have any formal definition of, or connected with, the term
"Lagrange Point", and if so where is it?

--
(c) John Stockton, nr London, UK. Mail via homepage. Turnpike v6.05 MIME.
Web http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms and links;
Astro stuff via astron-1.htm, gravity0.htm ; quotings.htm, pascal.htm, etc.

On Mon, 18 Feb 2013 20:14:58 +0000, Dr J R Stockton
wrote:

Does the IAU have any formal definition of, or connected with, the term
"Lagrange Point", and if so where is it?

I don't know, but I doubt it, for the simple reason that the term is
unambiguous and well described by conventional orbital mechanics (see,
for example, the Wikipedia article on the subject). Defining the term
in formal nomenclature seems as unnecessary as defining something like
"semi-major axis".

"Dr J R Stockton" wrote in message
nvalid...

In sci.astro.amateur message
t, Sun, 17 Feb 2013 07:54:46, Paul Schlyter posted:

On Sat, 16 Feb 2013 17:36:04 -0700, Chris L Peterson
wrote:
On Sat, 16 Feb 2013 22:11:54 +0100, Paul Schlyter
wrote:

What's thé formal definition of fireball??

The IAU formally defines a fireball as any meteor brighter than the
brightest planet, which is generally taken as magnitude -4.

That's the definition of bolide too: a meteor brighter than Venus.

"Bolide" is sometimes used by astronomers in reference to a fireball
that is observed to break up, and it is used by geologists in
reference to a crater forming object.

I think we can find other uses of "fireball" as well, particularly by
non-astronomers...

Does the IAU have any formal definition of, or connected with, the term
"Lagrange Point", and if so where is it?

--
================================================== ==============

There are five, two of which are trojans. They are all special planar
solutions
to the three body problem for which no general solution exists.
See Lorenz butterfly,
http://en.wikipedia.org/wiki/Lorenz_system
see
http://faculty.ifmo.ru/butikov/Proje...llection6.html

-- This message is brought to you from the keyboard of
Lord Androcles, Zeroth Earl of Medway.
When the fools chicken farmer Wilson and Van de faggot present an argument I
cannot laugh at I'll retire from usenet.


-- This message is brought to you from the keyboard of
Lord Androcles, Zeroth Earl of Medway.
When the fools chicken farmer Wilson and Van de faggot present an argument I
cannot laugh at I'll retire from usenet.

In sci.astro.amateur message
, Mon, 18 Feb 2013 17:03:54, Chris L Peterson
posted:

On Mon, 18 Feb 2013 20:14:58 +0000, Dr J R Stockton
wrote:

Does the IAU have any formal definition of, or connected with, the term
"Lagrange Point", and if so where is it?

I don't know, but I doubt it, for the simple reason that the term is
unambiguous and well described by conventional orbital mechanics (see,
for example, the Wikipedia article on the subject). Defining the term
in formal nomenclature seems as unnecessary as defining something like
"semi-major axis".


First, see my Web site :
http://www.merlyn.demon.co.uk/gravity4.htm ff.

Secondly, I am familiar with that Wikipedia page; my name appears in the
Article and the Discussion, both of which I have in part edited. By the
way, it is wrong to say "the Wikipedia article on the subject"; in
general, there are many pages on any subject, in many languages, often
written independently or partly so - and in this case about 40.

Thirdly, the Wikipedia page is considerably in error.


A common "definition" refers to the solutions of the circular restricted
three-body problem. But it is generally accepted (a) that Lagrange
points exist in the Solar System, with some occupied, (b) that there are
no truly circular orbits in the Solar System. Some, I think, consider
the true orbits to be approximately circular; but circularity is
unnecessary for a well-considered solution. Likewise for "restricted",
in that restriction is not necessary for solution.

Another "definition" is that they are the five points that Lagrange
discovered. But I am satisfied that he only wrote one paper - certainly
only one well-known paper - related particularly to them. In that paper
he discovered two constant-pattern configurations each of three bodies,
total six (and did not restrict, and did not need circularity). The
final step to the five points for two massive bodies and a particle is
trivial; but he did not take that step. In addition, he could NOT have
discovered L1 & L2, since Euler did that a few years earlier in E.304
(and omitted the trivial step of discovering L3).

Lagrange discovered the two configurations in Chapter 2, using the
compendious work of Chapter 1 (which he also used in Chapters 3 & 4).
Chapter 1 attempted the fully-general three-body problem, starting in an
unexpected manner. By using that manner but ignoring the general case,
the constant-pattern solutions can easily be shown, without circularity
or restriction.

So, as an extreme - consider the case of three bodies, all massive,
released at rest at the corners of an equilateral triangle. Their
motion is just as well described by Lagrange's work (and by the
simplified form) as are those of natural Trojans and of, for example,
SOHO. Therefore, they fundamentally have an equal claim to be called
Lagrange Points - but those who have not read Lagrange 1772 1 & 2 will
not like that.

Therefore, the IAU needs a definition, independently of whether it wants
one.

Those contemplating a reply should first read the first half of Lagrange
1772; and, if applicable, also E.304.

--
(c) John Stockton, nr London, UK. Mail via homepage. Turnpike v6.05 MIME.
Web http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms and links;
Astro stuff via astron-1.htm, gravity0.htm ; quotings.htm, pascal.htm, etc.
No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News.

On Feb 19, 1:03*am, Chris L Peterson wrote:
On Mon, 18 Feb 2013 20:14:58 +0000, Dr J R Stockton

wrote:
Does the IAU have any formal definition of, or connected with, the term
"Lagrange Point", and if so where is it?

I don't know, but I doubt it, for the simple reason that the term is
unambiguous and well described by conventional orbital mechanics (see,
for example, the Wikipedia article on the subject). Defining the term
in formal nomenclature seems as unnecessary as defining something like
"semi-major axis".

What you are actually saying is that even though Langrangians only
exist inside the heads of mathematicians,they have a reality that is
so certain that they are equivalent to a physical term like
'orbit'.This is actually a modern phenomena that the wider readership
probably are unaware of and I remember reading about these things in
1983 -

"A Langrangian is not a physical thing;it is a mathematical thing - a
kind of differential equation to be exact.But physics and maths are so
closely connected these days that it is hard to separate the numbers
from the things they describe.In fact,a month after [Philip]
Morrison's remarks,Nobel Prize winner Burton Richter of the Stanford
Linear Accelerator Center said something that eerily echoed it: "
Mathematics is a language that is used to describe nature" he said
"But the theorists are beginning to think it is nature.To them the
Langrangians are the reality " Discover Magazine ,1983

How to conjure a mathematical thing into a physical thing extends into
modeling everything nowadays up to including climate where no
intepretative restraints exist.