A nebula or not ... Tarantula

[Allan_L]

After reading another thread about the LMC,
I did a further little reading and was surprised to find the reference in several places, that the Tarantula Nebula is within the LMC.



Sorry for my ignorance, but I have been taught that anything referred to as a nebula lies within the Milky Way Galaxy.



But now this seems to be saying that the Tarantula Nebula is actually within the neighbouring galaxy of the LMC. And is located 160,000 light years from us (same distance as is quoted as the distance to the LMC.)

Sorry if this is a dumb question, but how can both statements be true.? :confused2:

[julianh72]

A nebula is a cloud of gas and / or dust which is visible in the night sky either as an indistinct bright patch or as a dark silhouette against other luminous matter. Most nebulae within the Milky Way are described as "faint fuzzies" for a good reason, as are most galaxies, so there are very few nebulae in other galaxies which are easily observable with typical amateur equipment - and the Tarantula is the best. It is so intrinsically bright that if it were as close to Earth as the Orion Nebula, it would cast shadows at night!

If you've got access to a really big telescope, there are some other beauties to be found in the LMC & SMC - e.g. check out "The Odd Couple", which also lies in the LMC:
http://www.eso.org/public/news/eso1335/
(The image in the article was taken with the European VLT, which has an 8.2 metre mirror!)

[julianh72]

P.S. Don't forget that the Andromeda Galaxy (M31) used to be known as the Andromeda Nebula, until the 1920s, when its true nature was confirmed.

[Allan_L]

Thanks for your reply Julian, but you seemed to miss the point I was asking about...



Tarantula not in Milky Way, but still referred to as Nebula.?

So has that "rule" been relaxed, or just ignored, or what?

[pixelsaurus]

What is the source of this comment?

[gary]

Hi Allan,

This rule never existed.

But our concept of the hierarchy of objects in the universe radically
changed in the 1920's.

Nebula can be present anywhere in the universe.

As Julian explained, there was a major philosophical change in our
comprehension of the universe when Hubble first realized that
what we now refer to as galaxies were in fact outside of the Milky Way.

Before then, most astronomers believed that the Milky Way was the
entire universe and they classified all objects that were nebulous -
including what we now know as galaxies - as nebulae. *

Just before Hubble's seminal discovery, the term "non-galactic"
actually meant "away from the galactic plane".

Post the Edwin Hubble Cepheid variable/redshift discovery, what
we today refer to as galaxies were then called "extragalactic nebulae".

It was not until after Hubble's death in 1953 did the term "galaxy"
become widespread. [Reference - Steven J. Dick, Discovery and Classification
in Astronomy: Controversy and Consensus, Cambridge University Press, page 122].

Since the LMC and SMC are relatively close, many nebulae can be readily resolved in them
with amateur instruments.

With more distant galaxies, resolving nebulae within them becomes more difficult, but they
are still called nebula.

Hope this helps.

* Footnote
Astronomer Heber Curtis argued in 1920 with Harlow Shapley that "spiral nebula" were "island universes" outside of the Milky Way.

[DJT]

Pfft! 0.2 metre mirror..Bottom left corner, GSO RC8. ;)

NGC2029 Dragons Head nebula in the LMC (http://astrob.in/228066/0/)

Granted, their resolution is a tad better and their processing is rather good...

[Allan_L]

https://cosmology.carnegiescience.edu/timeline/1929/nebulae

[wayne anderson]

It is interesting how what is defined as a Nebula changes with time and knowledge, when originally discovered the Triangulum galaxy M33 was defined as a Nebula then re defined as a Galaxy now the M33 Galaxy is known to also contain the NGC 604 Nebula.

http://hubblesite.org/newscenter/archive/releases/1996/27/image/a/

[Renato1]

Hi Allan,
I think it better to just use the Wikipedia definition,
"A nebula (Latin for "cloud";[2] pl. nebulae, nebulæ, or nebulas) is an interstellar cloud of dust, hydrogen, helium and other ionized gases."

Otherwise, nebula like any emission nebula, planetary nebula or supernova nebula found in another galaxy, would have to have new names - for no apparent reason.
Regards,
Renato

[tlgerdes]

One other interesting thing I was told about the tarantula nebula, if it was transposed to our galaxy and placed as far from earth as M42, it would be visible in daylight on earth and fill a 1/4 of the sky.

[bugeater]

My guess is someone paraphrased without really understanding the material.

Plus I wonder if the meaning of nebula hasn't changed at all - it was just worked out that some of those classified as such (i.e. galaxies) didn't fit the definition.

When I was in undergrad I read some of the key original papers studying viruses. It was fascinating because at the time of them writing the papers they didn't even know what viruses were, but I did. It was weird. I suspect the early papers looking at galaxies would be similar.

[Pradeep]

http://cdn.spacetelescope.org/archives/images/screen/heic1011d.jpg