V838 Monocerotis

* Stupendous_Man:
I attemped to show how material located a bit closer to us than the
star could cause light echoes to _appear_ to be superluminal.

Yes, it can in general, but (1) that's a different case, and (2) it
wasn't discussed in your posting,

quote
If astronomers on Earth think that the dust cloud "c" is
at the same distance as the star (instead of being somewhat
closer to Earth), and they try to use the apparent angular
separation of the cloud from the star and the star's distance
to determine the linear separation of the cloud from the star,
what distance will they calculate?
/quote

so it's difficult to know what was attempted.


I am writing this for the benefit of readers of this thread; I've given up on
trying to reason with Mr. Steinbach.

I'm sorry to hear that. Your attempted explanation, postulating an
in-between dust cloud, was a good idea. Perhaps some other similarly
good idea would actually work out when the numbers are included?

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* Stupendous_Man:
I attemped to show how material located a bit closer to us than the
star could cause light echoes to _appear_ to be superluminal.

Alf P. Steinbach wrote:
Midway: a factor of roughly 2, or a little more, max 3, to get the
lightspeed down to lightspeed from the apparent 1.5 ly in 7 months

This is incorrect.

What concrete light paths are you proposing, then?

Numbers would be nice.

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* Alf P. Steinbach:
* Stupendous_Man:
I attemped to show how material located a bit closer to us than the
star could cause light echoes to _appear_ to be superluminal.

Yes, it can in general, but (1) that's a different case, and (2) it
wasn't discussed in your posting,

quote
If astronomers on Earth think that the dust cloud "c" is
at the same distance as the star (instead of being somewhat
closer to Earth), and they try to use the apparent angular
separation of the cloud from the star and the star's distance
to determine the linear separation of the cloud from the star,
what distance will they calculate?
/quote

so it's difficult to know what was attempted.


I am writing this for the benefit of readers of this thread; I've given up on
trying to reason with Mr. Steinbach.

I'm sorry to hear that. Your attempted explanation, postulating an
in-between dust cloud, was a good idea. Perhaps some other similarly
good idea would actually work out when the numbers are included?

Hm, I'll partially answer my own original posting.

Assuming the dust cloud "c" _is_ centered on the star, and furthermore
that it's between 6 to 8 ly in size (before it gets so thin that we
don't see a light reflection), then the following JavaScript program,

var r = 7.5; // radius of dust cloud
var distance = 20000; // distance to star

function pathLength( apparentSize )
{
var x1 = Math.sqrt( r*r - apparentSize*apparentSize )
var x2 = distance - x1
var y = apparentSize*x2/distance;
return Math.sqrt( x1*x1 + y*y ) + Math.sqrt( x2*x2 + y*y );
}

function writeLine( line )
{
WScript.Echo( line ); // For Windows script host.
}

var h; // apparent size of echo
var d0 = pathLength( 2 );

for( h = 2; h = 4; h += 0.1 )
{
var apparentSize = h
var deltaPathLength = pathLength(h)-d0
writeLine(
apparentSize.toFixed( 1 ) + " " +
deltaPathLength.toFixed( 5 )
);
}

calculates agreement with the reported echo sizes, an increase in the
light path of about 0.6 ly between the apparent 2 ly echo radius and the
apparent 3.5 ly echo radius (over about 7 months, which works out as
7/12 = cirka 0.6 year); the first column is apparent diameter of the
echo, and the second the extra light path relative to echo radius 2:

2.0 0.00000
2.1 0.02841
2.2 0.05832
2.3 0.08976
2.4 0.12275
2.5 0.15730
2.6 0.19345
2.7 0.23121
2.8 0.27061
2.9 0.31168
3.0 0.35446
3.1 0.39896
3.2 0.44523
3.3 0.49331
3.4 0.54322
3.5 0.59502
3.6 0.64875
3.7 0.70445
3.8 0.76218
3.9 0.82199

So now I think I understand the superluminal echo size (although six to
eight ly of dust centered on the star is difficult to imagine!); what I
still don't understand is the persistent and uniformly increasing in
size ragged "holes" in the echo -- how can those holes come to be?

--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?