Distance discreppancy

[bloodhound31]

Cut and paste from a google search.

Located in the constellation Sagittarius, the Trifid nebula is a beautiful combination of reflection nebula (blue) and emission nebula (red).

The nebula's distance is rather uncertain, with values between 2,200 light years (Mallas/Kreimer; Glyn Jones has 2,300) and about 7,600 light years (C.R. O'Dell 1963). The Sky Catalog 2000 gives 5,200 light years, a value which is also used by Archinal and Hynes (2003). The WEBDA database has 3140, the Hubble Press Release of Jeff Hester (STScI-PRC99-42) gives "about 9000" light years.

So what's the story?

Baz.:D

[xelasnave]

Probably the different between imperial and metric light years Baz...
just joking as I have no ideas for you..
alex

[JD2439975]

:rofl::rofl:

[bloodhound31]

Being in our local neighborhood, you'd think they'd know wouldn't you?

I mean, how can they expect us to entertain theories of matters much further away, when they can't even get the distance of a local nebula right?

2,200, to 9000 light years between a couple of spiral arms of one galaxy is a huge margin of error, let alone extrapolating these distances across the entire universe to the beginning!

Where lies the error?

[sjastro]

Paradoxically it's easier to measure more distant objects like galaxies simply because there is a far greater probability of finding Cepheid variables and/or type 1 supernovae which allow distances to be calculated using the distance/luminosity relationship.

For very distant galaxies that are not gravitationally bound to other galaxies, distances are even easier to calculate, the red shift of the galaxy is measured and the distance is calculated using Hubble's Law.

The trouble with objects like the Trifid Nebula is that they are outside the range of calculating distance using parallax. Combine that with the lack of candidates such as Cepheid variables makes the distances quoted an estimate.

Regards

Steven

[Robh]

As someone with a maths/science background it continually amazes me that sources quote distances to say the nearest 10 or 100 light years when the accuracy to the nearest 1000 light years is in question. The figures quoted are very misleading and lead one to question all data even though some may be more reliable than others. The same problem exists for visual magnitudes of larger objects such as galaxies where magnitudes are quoted to the nearest 0.1 and yet sources can vary by 1 magnitude.
Distances of objects are usually more accurately stated as e.g. Small Magellanic Cloud 197 + or - 9kly, which gives some indication of the reliability of the figures.

In my opinion, distances, masses, magnitudes etc. need to be more rigorously stated so that we all know in what areas the measurements are fairly accurate as against where they are just calculated guesses.

Regards, Rob.

[bojan]

Anyone tried to see what Pleiades look like from side stand point, using Celestia (which is using Hipparkos data)?
Well, they look really elongated along our line of sight. The uncertainty is like 20% or more.
The reasons are the same: Pleiades are just out of range for parallax method, and there are plenty binaries and multiple stars in the cluster.
But once you know the limitations of methods used to acquire stellar distances, all makes sense.

[Robh]

You're so right!
"A man's got to know his limitations." (quote from Clint Eastwood in Magnum Force).
:D

Regards, Rob.