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flashgordon1952
2005-Mar-24, 04:02 PM
wow what a subject to get your teeth into ! How many and is there any idea how many known ones that are not mapped.. one thing thats has always puzzled me how they know that such in such planet is from one particular galaxy and are ther rogue planets out there that are not asteroids but actual planets. :ph34r:

antoniseb
2005-Mar-24, 04:38 PM
Originally posted by flashgordon1952@Mar 24 2005, 04:02 PM
one thing thats has always puzzled me how they know that such in such planet is from one particular galaxy and are ther rogue planets out there that are not asteroids but actual planets.
Hi flashgordon1952,

I'm not sure what you're talking about here. When have you read that some planet has been identified as from a particular galaxy? Do you mean in the microlensing observations by OGLE etc, or the recent Einstein's Cross article here on UT?

As to Asteroids vs. Rogue planets... Again, I can't tell exactly what you're talking about. We can tell how far away asteroids are by their movements in their orbits, and have several ways to determine their size, the first of which is to guess how dark their surface is, and see how bright they look overall. There are no asteroids in our solar system that could actually be a rogue planet from another galaxy.

John L
2005-Mar-24, 08:57 PM
I think you're getting the solar system/galaxy/universe terms mixed up. The solar system is one single star (or a few stars orbiting each other) and the gas, dust, and planets that orbit only that star (or stars). A galaxy is a large concentration of millions to hundreds of billions of stars that orbit a mutual center of gravity, which has been found in many to contain a super massive black hole. The universe is EVERYTHING. All stars and galaxies and planets and asteroids reside within the one universe.

We can tell if something is close to the Earth or far away by how much it moves in the sky from night to night. If you look at it tonight and it is one degree to the left of a particular star, and the next night it is one degree to the right of that same star, then its apparent motion indicates it is very close. If it hardly moves at all it is probably very far away. By combining observations like this over an entire year, comparing the measured positions, you can calculate the object's orbit either around our star, or around the galaxy in general.

Based on its brightness and its motion we can then determine its size. An object that appears to move a lot asa we measure its motion and is very dim is probably very small, like a comet or asteroid. An object that is very bright and moves a lot is probably pretty big like a planet. If the object doesn't appear to move much at all, then it is porbably very far away, like another star or even another galaxy.

astromark
2005-Mar-27, 02:08 AM
As for your question? We can see about 13.7 billion light years. beond that distance / time we are not seeing galaxies. Its been sagested we are looking at the remnants of the Big Bang and the background of dark matter. The sky is full of galaxies. In every direction. millions apon millions. the ferther away they are the faster they seem to be recieding away from us. With ever changing equipment we are able to see far more of this stuff than ever before. Unrefutable facts about the size and number of Galaxies observed are enormose, and growing. now what was your question again? how many? zillions and then more.

zephyr46
2005-Apr-17, 06:46 AM
I'll have a wack at this one,

HERE (http://www.electrickiva.com/chs/gmalone/2003_Spring/unit3/universe_grandtour.htm)

Is a set of maps of pretty much what we know.

2df (http://www.mso.anu.edu.au/2dFGRS/)

Here (http://www.anzwers.org/free/universe/supercls.html) is a list of some of the named superclusters of galaxies.

In 3 dimensions (http://hometown.aol.com/nlpjp/map13.htm).

Or if you are serious,

Images (http://nedwww.ipac.caltech.edu/level5/catalogs.html) from Level 5 (http://nedwww.ipac.caltech.edu/level5/index.html)

Sedna is the farthest asteroid I know of, but there are dust disks around other know star systems the extrasolar visions identifies Q0957+561 (http://www.extrasolar.net/planettour.asp?StarCatID=extragalactic&PlanetID=74), A planet in a forground galaxy micro lensing a quasar, so beleive that one if you are an optimist :)

Oh check THIS ! (http://www.noao.edu/image_gallery/html/im0862.html) out! MAD :)