How do we know the borders of our solar system?

Question

How do astronomers know where the Milky Way ends and another galaxy begins? Also what have astronomers seen above and below the Milky Way?

Answer 1

You asked about the borders of our solar system, but the additional part of the question refers to galaxies. So perhaps you're confused about the difference.
A galaxy is like a huge city of stars.
A solar system is like a tiny neighbourhood in the galaxy.

There is a lot of empty space between the galaxies, its fairly clear where the Milky Way ends and the next nearest galaxy begins. The closest is the Sagittarius Dwarf galaxy, and its over 50,000 light years away. The closest major galaxy is Andromeda, over 2 million light years away.

Our solar system is less than 2 light years across (when you include the diffuse Oort Cloud). The next closest star is over 4 light years away, so there is a lot of room between star systems.

Answer 2

Are you asking about the solar system or the galaxy?

the solar system is bounded by the heliopause according to general scientific consensus.

The galaxy doesn't necessarily have a firm ending, but the nearest full galaxy is so far away, that there is no chance of confusing the 2. It's like if you see a cloud in the eastern sky and another one completely on the western side of the horizon. If you are right up on the cloud, it's hard to point to a line that is the end, but it's clear that it's separate from the other cloud.

But even scientists can't necessarily agree on a definition of a galaxy. There are some "galaxies" that are satellites of the milky way. Some might not consider them galaxies.

http://en.wikipedia.org/wiki/List_of_nearest_galaxies

Answer 3

Listen to Ronin
The Oort cloud isn't the boundary. The heliopause is the boundary between the outward pressure of particles being ejected from our sun and the particles being ejected by the next star. It is the furthest distance at which our sun has influence.

The boundary between galaxies is more difficult to determine.
The Milky Way has two satellite galaxies called the Magellanic clouds. There is also the possibility that there are the remnants of other galaxies within the Milky Way. Galaxies collide with each other and some gobble up the smaller galaxy.

Answer 4

The borders of our Solar System are clearly posted (by the Oort Cloud ☺) to try and keep illegal aliens out. But nobody really enforces it much, so we have a problem with them.

Galaxies (such as our own Milky Way) are just huge collections of stars all torating about he center of mass of the galaxy. And the distance(s) between galaxies is --really-- huge. Much more so than the distance(s) between stars.

Looking outwards from the Milky Way, we see more galaxies in all directions. Galaxies close to us include the well-known 'Andromeda' nebula as well as the 'Magellenic Clouds' and a couple of others which only have catalog references. Galaxies appear to be loosely aggregated into what are called 'groups' and groups, in turn, are aggregated into what are called 'super clusters'.

Doug

Answer 5

We can see them, including some objects in the Oort Cloud, the designated "boundary" of our solar system

We can measure distances by a triangulation system called the VLA (Very Large Array).

Please look this stuff up using Google. I don't want to spend half the night bringing you on board with present technology.

Answer 6

Galaxies are in groups, however they are still far far apart. Stars do not fall out of galaxies due to their rotation...Therefore there are great voids of space where nothing but dust or plain space exist.