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Read this in Patrick Moores book and don't understand it....

tenbyfifty

By tenbyfifty
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tenbyfifty

tenbyfifty

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Its in the Phillips guide to the stars and planets on the page about star clusters, it says:

Globulars are commonest in the southern hemisphere of the sky, giving the first definitive proof that the Sun lies

well away from the galactic centre.

It also says that globular clusters lie in a halo around the galaxy but I can't marry this fact with the above quote.

Am I missing something that's bleedin' obvious to everyone else?

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The Warthog

The Warthog

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I think it's a matter of geometry. The galactic centre lies in the south, just off the spout of the Sagittarius teapot. Therefore, the Earth's north pole leans away from the galactic centre, and since the globulars are fairly evenly distributed about the galactic centre, the south pole is pointing towards more of them than the north pole is. There are still quite a lot of globs visible from the northern hemisphere, though.

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tenbyfifty

tenbyfifty

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I think it's a matter of geometry...

Yes that seems to make sense. Thanks for that.

Does that mean its harder to see galaxies when you look towards the centre coz there are many more

stars in the way or is there still plenty of space between the trees?

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Astroman

Astroman

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I think it's a matter of geometry...

Yes that seems to make sense. Thanks for that.

Does that mean its harder to see galaxies when you look towards the centre coz there are many more

stars in the way or is there still plenty of space between the trees?

WH is right about the apparent discrepency in distribution of globulars. They're fairly evenly spaced, no pun intended, but since we're tilted with respect to the galactic center, they appear skewed.

You can't see galaxies toward the center of our galaxy because there's just too much dust, gas and stars between us and them. In fact, you can't see stars in that direstion that are farther than a few thousand light years away for the same reason. Keep in mind, the MW center is about 20,000 ly away, and we can only see about 1/4 of the way there. Infrared satellites and ground based observatories are able to penetrate this dust to reveal what's there, but visually, it ain't gonna happen, as they say.

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FLO

FLO

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You can't see galaxies toward the center of our galaxy because there's just too much dust, gas and stars between us and them. In fact, you can't see stars in that direstion that are farther than a few thousand light years away for the same reason.

The Nearby Galaxies Catalog has 3D locations for the closest 68,000 galaxies to Earth. This data forms a cube of galaxies within an area of 700 million light years centered on Earth. A visual navigable representation of this index can be found in the planetarium computer software Starry Night Pro, where the data is called the Tully Database.

http://en.wikipedia.org/wiki/R._Brent_Tully

I have posted the image here because, when rotated to a particular point, it clearly shows the 'gap' that is a result of us not being to see through the dust clouds of our own galaxy. (Earth is in the center)

image.jpg

Image from StarryNight PRO

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tenbyfifty

tenbyfifty

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The Nearby Galaxies Catalog has 3D locations for the closest 68,000 galaxies to Earth. This data forms a cube of galaxies within an area of 700 million light years centered on Earth. A visual navigable representation of this index can be found in the planetarium computer software Starry Night Pro, where the data is called the Tully Database.

Brilliant!! I've been wondering what the Tully DB was , now I know. This is what makes astronomy interesting, when your view of what's out there changes on a regular basis.

Here's a more light hearted question:

How close do you reckon a face on spiral galaxy, about the size of our own milky way, would have to be in order to fill the square of Pegasus? Do you think a galaxy could be this close without interacting with our own?

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FLO

FLO

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[The Nearby Galaxies Catalog has 3D locations for the closest 68,000 galaxies to Earth.

I thought NGC was "New General Catalouge"? Sorry to be picky :laugh:

The quote was from from Wikipedia ... I think the NGC catalogue you refer to is a different one.

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FLO

FLO

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I am pretty sure that the Tully database (called that to prevent confusion, I guess) is exclusive to the StarryNight Pro range of PC planaterium software. Using the software, you can actually enter into the mass of galaxys and travel around amongst them... 8)

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Astroman

Astroman

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Ok, a couple things.

The NGC referred to by numbers of deep sky objects is The New General Catalog, compiled by Johann Dreyer in the mid 19th century. He was attempting to combine a bunch of observing notes of as many observers as possible into a single catalog of deep sky objects. Here's a link to a web site that's trying to rconcile all this data from all these different observers to "clean up" the errors in the original and the additional IC, or "Index Catalog". One of the main guys in here, Bob Erhman was responsible for me joining the Saguaro Astronomy Club back in 1996. The Nearby Galaxies Catalog is something else that I hadn't heard of. I suspect it's native to the program software mentioned.

To answer tenbyfifty's question, a galaxy close enough to cover Pegasus' square would have to be just over 43,000 light years away, if it were the size of our Milky Way. This is less than half the distance to the Magellanic Clouds. There's no way it could NOT be interacting with us at that range. Both galaxies would be torn apart by tidal forces and would not resemble the neat spirals they'd have been before. Google "Hickson Groups", or "Arp Galaxies" for examples. Scary stuff.

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tenbyfifty

tenbyfifty

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To answer tenbyfifty's question, a galaxy close enough to cover Pegasus' square would have to be just over 43,000 light years

Any chance you could tell us how get that number Astroman? Anthony has a formula but it seems to give

a substantially larger figure asssuming the square is 20 degrees across and the milky way is 100,000 lys across.

No idea which is correct :?

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Astroman

Astroman

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Sure. I used the width of Pegasus-15º30'. The formula for angular distance is a=s/d, where a=Angular size in radians, s=size of object in ly and d=distance. a=15º30' in radians is pi/8=.392857. Size of MW is ~110,000ly. Solve for distance = .392857X110,000=43,213 ly.

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