How is it known that the Milky Way is a spiral galaxy ?

"Weatherlawyer" wrote in message
oups.com...

Mike Dworetsky wrote:

I thought that it was determied a spiral by Herschel and his
sister..er..er ..Herschel.

Caroline. No, William Herschel determined by star counts that our star
system was somewhat flattened, and a few thousand light years* across,
but
he was not able to determine anything about spiral structure. Lord Rosse
was the first to observe spiral structure visually in an external galaxy,
M51, at least half a century after Wm. Herschel. But at that time the
true
nature of nebulae was unknown.

The Milky Way was widely believed to be a spiral by analogy with external
galaxies before the radio astronomy result, but only after Hubble's
discovery of the true distance to nearby galaxies.

*The underestimate was due in part to not realising the importance of
interstellar dust in obscuring the view of distant stars.

It strikes me that we still don't know all we think we do about our
home despite all the theories. We don't know for a fact what is at the
heart of the sun never mind nebulae.

When god parted the waters, was this space dust a layer of the watery
deep? God knows. No man alive can say at any rate. The only thing we
can say for certain apparently, is that we still don't have a parallax
on any of the stars yet.


You have been advised otherwise in the past.

The first measurement of stellar parallax was made in 1838 by FW Bessel.

"Weatherlawyer" wrote in message
oups.com...

Mike Dworetsky wrote:

I thought that it was determied a spiral by Herschel and his
sister..er..er ..Herschel.

Caroline. No, William Herschel determined by star counts that our star
system was somewhat flattened, and a few thousand light years* across,
but
he was not able to determine anything about spiral structure. Lord
Rosse
was the first to observe spiral structure visually in an external
galaxy,
M51, at least half a century after Wm. Herschel. But at that time the
true
nature of nebulae was unknown.

The Milky Way was widely believed to be a spiral by analogy with
external
galaxies before the radio astronomy result, but only after Hubble's
discovery of the true distance to nearby galaxies.

*The underestimate was due in part to not realising the importance of
interstellar dust in obscuring the view of distant stars.

It strikes me that we still don't know all we think we do about our
home despite all the theories. We don't know for a fact what is at the
heart of the sun never mind nebulae.

When god parted the waters, was this space dust a layer of the watery
deep? God knows. No man alive can say at any rate. The only thing we
can say for certain apparently, is that we still don't have a parallax
on any of the stars yet.


An odd mix of bad theology and even worse science, Sunshine. Never heard of
the Hipparcos Satellite?

--
Mike Dworetsky

(Remove "pants" spamblock to send e-mail)

Hi,
I'm an absolute newbie
I just wonder how light propagates 13 billion years to hit our retina,
through void, with nothing to prop against?
And as in a crime novel, "cherchez la femme", if you look at the
universe, it's packed with light no matter
where you go, why is light so meaningful to understand the system?

De la discussion jaillit la lumière

Ishke Baha

In message , Mike Dworetsky
writes
"Weatherlawyer" wrote in message
roups.com...

When god parted the waters, was this space dust a layer of the watery
deep? God knows. No man alive can say at any rate. The only thing we
can say for certain apparently, is that we still don't have a parallax
on any of the stars yet.


An odd mix of bad theology and even worse science, Sunshine. Never heard of
the Hipparcos Satellite?


Satellite? They didn't have satellites in the 19th century :-)
I'd guess that a well-equipped amateur could do it, but a quick web
search didn't find any recent examples.

In article , Mike Dworetsky
wrote:




Caroline. No, William Herschel determined by star counts that our star
system was somewhat flattened, and a few thousand light years* across, but
he was not able to determine anything about spiral structure. Lord Rosse
was the first to observe spiral structure visually in an external galaxy,
M51, at least half a century after Wm. Herschel. But at that time the true
nature of nebulae was unknown.

The Milky Way was widely believed to be a spiral by analogy with external
galaxies before the radio astronomy result, but only after Hubble's
discovery of the true distance to nearby galaxies.

*The underestimate was due in part to not realising the importance of
interstellar dust in obscuring the view of distant stars.

This was all part of the Great Debate of the early 20th Century as I
recall as well. Curtis and Shapley arguing over whether the spiral
nebulae were external star systsems, and both being half right and half
wrong with their assertions as well, as I recall.

A fascinating read, particulary with relevance to the debate that went
on the nature of our galaxy.

--
The true enemy of science is psuedoscience...

In article , Mike Dworetsky
wrote:

"Weatherlawyer" wrote in message
oups.com...

When god parted the waters, was this space dust a layer of the watery
deep? God knows. No man alive can say at any rate. The only thing we
can say for certain apparently, is that we still don't have a parallax
on any of the stars yet.


An odd mix of bad theology and even worse science, Sunshine. Never heard of
the Hipparcos Satellite?

Yep - and it doesn't even need that fancy-pants satellite ;-)

http://www-spof.gsfc.nasa.gov/stargaze/Sparalax.htm

How far to a Star?
When estimating the distance to a very distant object, our "baseline"
between the two points of observation better be large, too. The most
distant objects our eyes can see are the stars, and they are very far
indeed: light which moves at 300,000 kilometers (186,000 miles) per
second, would take years, often many years, to reach them. The Sun's
light needs 500 seconds to reach Earth, a bit over 8 minutes, and about
5.5 hours to reach the average distance of Pluto, the most distant
planet. A "light year" is about 1600 times further, an enormous
distance.

The biggest baseline available for measuring such distances is the
diameter of the Earth's orbit, 300,000,000 kilometers. The Earth's
motion around the Sun makes it move back and forth in space, so that on
dates separated by half a year, its positions are 300,000,000
kilometers apart. In addition, the entire solar system also moves
through space, but that motion is not periodic and therefore its
effects can be separated.

And how much do the stars shift when viewed from two points
300,000,000 km apart? Actually, very, very little. For many years
astronomers struggled in vain to observe the difference. Only in 1838
were definite parallaxes measured for some of the nearest stars--for
Alpha Centauri by Henderson from South Africa, for Vega by Friedrich
von Struve and for 61 Cygni by Friedrich Bessel.

--
The true enemy of science is psuedoscience...

In article .com,
wrote:

Hi,
I'm an absolute newbie
I just wonder how light propagates 13 billion years to hit our retina,
through void, with nothing to prop against?
And as in a crime novel, "cherchez la femme", if you look at the
universe, it's packed with light no matter
where you go, why is light so meaningful to understand the system?

De la discussion jaillit la lumière

Ishke Baha


Light is a self-propagating electromagnetic wave, and unlike sound
waves doesn't need a medium to wave against, per se. Light is a
electric and magnetic wave at right angles to each other, and to the
direction of motion.

The universe is currently dark energy dominated, but was matter
dominated and in the early days was radiation dominated. A quick readup
on the cosmic microwave background would give you a good starter to
cosmology.

--
The true enemy of science is psuedoscience...

Phineas T Puddleduck wrote:
In article .com,
wrote:

Hi,
I'm an absolute newbie
I just wonder how light propagates 13 billion years to hit our retina,
through void, with nothing to prop against?
And as in a crime novel, "cherchez la femme", if you look at the
universe, it's packed with light no matter
where you go, why is light so meaningful to understand the system?

De la discussion jaillit la lumière

Ishke Baha


Light is a self-propagating electromagnetic wave, and unlike sound
waves doesn't need a medium to wave against, per se. Light is a
electric and magnetic wave at right angles to each other, and to the
direction of motion.

The universe is currently dark energy dominated, but was matter
dominated and in the early days was radiation dominated. A quick readup
on the cosmic microwave background would give you a good starter to
cosmology.

--
The true enemy of science is psuedoscience...

Hi,
Light is a self-propagating electromagnetic wave
How can it propagate without consuming energy?
I thought there was no such thing as perpetual movement

currently dark energy dominated
So when electromagnetic waves travel 4 billion years through o.k. void,
what happens when they enter dark energy territory?

The true enemy of science is psuedoscience
Quote: "Philosophy [..] might turn outside to an investigation of the
universe ....
and where called Natural philosophers...
the modern word that is used in its place -science ..."

Isaac Asimov, Understanding Physics, motion sound and heat

Mehr Licht! - Goethe's last words

Phineas T Puddleduck wrote:

Light is a self-propagating electromagnetic wave, and unlike sound
waves doesn't need a medium to wave against, per se. Light is a
electric and magnetic wave at right angles to each other, and to the
direction of motion.

What light might be, remains to be seen (to coin a phrase.) I would
have considered it a measure of the power of heat in some way but how
can you say it is en example of elecromagnetic wave?

Get real. Something is either moving or the path it takes has
undulating features it can not "be" both.

Mike Dworetsky wrote:

When god parted the waters, was this space dust a layer of the watery
deep? God knows. No man alive can say at any rate. The only thing we
can say for certain apparently, is that we still don't have a parallax
on any of the stars yet.


An odd mix of bad theology and even worse science, Sunshine. Never heard of
the Hipparcos Satellite?

Rewind we. Is that the one they fired a slug into a snow cloud from? Or
would you prefer it called an asteroid?

You can call it the hemmaroid of god if you like for what the
difference was. It seemed very biblical to me, oh troll of very little
brain.