Astronomy questions (edit: questions answered Thanks guys!)

[trancejeremy]

Personally, I think you would use radio astronomy, not visual, to figure out where you were. For outside the galaxy, quasars. Inside, there's a number of unusual objects that you could probably spot fairly easy if you look at various different wavelengths.

Parallax is just the difference in angle between viewing distances, period (like if you look through one eye, then the other). Anyway, given the large distances, the parallax might not be obviously noticeable, but it is still finite and measureable.

The ancient greeks didn't think stars were far away because they personally couldn't notice any parallax from them (when the earth is on opposite sides of the sun), but that's because their technology just wasn't good enough to measure it.

You probably could use it to figure out where you are, but it would be too time consuming, as there are a heck of a lot of normal stars in the galaxy, but only a relatively small number of unusual objects

 

[BiggusGeekus]

Also makes it interesting to calulate location, since from that vantage point, you might be able to see the Milky Way galaxy itself as a huge flattened spiral.

Really? That's cool. Would you be able to see it with the naked eye?

Actually, I don't know if I want them to see the Milky Way like that or not, but it'd be cool to keep my options open.

 

[BiggusGeekus]

M4 in the constellation Scorpius is the closest at 7,200 l-y.

OMG!

M4 would be one of the most splendid globulars in the sky if it were not obscured by heavy clouds of dark interstellar matter.

 

[WayneLigon]

A new question: I'm looking fora nice, firiendly G2 star that's at least 5,000 light years but not more than 15,000 light years from Earth? The distances aren't that important, but for story purposes a good 10,000 light years away would be nice. Under 1,000 would be pretty bad.

Just make one up; anything as dim as a G2 past a hundred light years doesn't have a name anyway, it has a catalog number like Gli68676+009.888 or other such gobbletygook I can find lots of lists of stars, but nothing measured in light years; all of them are plotted in ascension and declination and arc of this or that; I dunno how to traslate that to 'It's this far from Earth'.

 

[Pbartender]

Really? That's cool. Would you be able to see it with the naked eye?

Most likely... Draw a picture of a spiral-like galaxy on a paper plate, then look at the center with your eye about a quater-inch above the very outside edge. That'll give you a vague idea of what it might look like.

Actually, I don't know if I want them to see the Milky Way like that or not, but it'd be cool to keep my options open.

Well, of course, if no one else has ever seen the Milky Way from outside, how will they know which galaxy they are looking at. At first glance, it could be the Andromeda galaxy for all they know.

 

[Pbartender]

Your welcome...

Plus...

In 1987, the first millisecond pulsar was discovered in this globular cluster. This pulsar, 1821-24, is a neutron star rotating (and pulsating) once every 3.0 milliseconds, or over 300 times per second, which is even 10 times faster than the Crab pulsar in M1. A second millisecond pulsar was found in M28 later in the same year.

That gives your players a very distinctive and well known millisecond pulsar to calculate their position from, if they happen to notice it nearby. And especially if they can find the M28 globular cluster with it's millisecond pulsar to triangulate from. (Currently there are approximately only 130 millisecond pulsars known in globular clusters.)

 

[Baron Opal]

It's reading stuff like this, and the associated links, that make me wish I had a better head for math. I love this stuff!

 

[Umbran]

The difference of angles (the term has escaped my undercaffinated brain at the moment, sorry) from one side of the galactic disk to the other isn't that dramatic, though.

Well, I wasn't thinking about using a parallax method. I was thinking of using triangulation. Assume you have a catalog filled with lots of known objects and their positions relative to Earth. Move to a new location. Find three (possibly two, or even just one, if you have other information) of the objects in your catalog (by details of spectra, pulse/variation rate, or other identifying characteristics). A bit of trigonometry will identify your new location relative to your old one.

This is where knowing *something* about your new location is important. It tells you which objects you should start looking for - The farther you have moved from your starting location, the farther out you need to look for your guides.

If you've moved clear across the visible universe, you need to start looking for quasars. If you've moved to another nearby galaxy, you need to look for other galaxies. If you're within our galaxy, you start looking for stars and pulsars. If you're still within the solar system, you need to start looking for planets...

 

[Matt Black]

I see that a lot of good answers have been given. But pedantry demands that I throw in my 2c.

Here are the methods you would use:

Within the galaxy:

Triangulation using the local group of galaxies and our own galactic center. Most usefully, Andromeda and the Magellanic Clouds. These alone would allow you to determine your position with high accuracy.

Alternatively, radio observations of 21cm emission from neutral hydrogen gas in the spiral arms. This has been used to accurately map the Milky Way's structure.

(Pulsars wouldn't be useful because you have to be aligned with their axial jets to see them. From any other point in the galaxy, chances are you won't see the ones that we can see from earth.)

Outside the galaxy, in the local universe:

If you're within a few hundred megaparsecs you could triangulate using the nearby clusters of galaxies. Fornax, Hydra, Virgo, etc. These are all very well studied and should be recognisable from any direction. That would give you a (very) rough location of the local group of galaxies. You would then search for pairs of spiral galaxies that matched Andromeda and the Milky Way. This would take a fair amount of time, because you'd need two wide-field surveys - one shallow, all-sky survey and one deeper survey over several arcminutes.

Beyond the local universe:

You're probably hosed. Your only real hope would be to do a massive, fairly deep survey of the sky and try to match the large-scale structure with that known from Earth-based surveys. You couldn't rely on things like quasars, which only have life-spans of 10 million years or so. The difference in light travel time means that an entirely different population of quasars would be visible from different points in space. Besides, quasars look very different depending on the angle that you view them.

 

[BiggusGeekus]

I see that a lot of good answers have been given. But pedantry demands that I throw in my 2c.

See, this is why I love the internet. Thanks man.