You don´t need to find the Halo to note the direction. See the panorama:Janus said:If it was me, I probably do something like this. First locate the direction to the Center of the Galaxy. This should be fairly easy by looking for the Halo of globular clusters around it, or assuming you have the equipment to do so, finding Sagittarius A.
First, you need a spectroscope. Then you need to distinguish the spectrum of Alnilam from other bright stars, nearby or far away. Finally you need to be sure it has not changed in these lightyears.Vanadium 50 said:From there I would go to an extraordinarily bright star, like Alnilam (Epsilon Orionis). That start would be really hard to miss - it's one of the very brightest in the galaxy and has a well-known spectrum.
snorkack said:First, you need a spectroscope.
You do. Because there are a lot of bright blue stars in Milky Way. You do not know which one you are looking at. The three stars of Orion´s belt look much the same, so look at the belt from a different direction, and it´s hard to be sure of identification.Vanadium 50 said:Hey, if the rules allow a starship, surely they allow a spectroscope. But I picked these stars because they are the brightest in the neighborhood. You don't need much more than "the really bright blue one over on the left" to identify them.
Yes. Which is why the angular direction from Sun is much better known one.Vanadium 50 said:The problem with distances to known objects is that we know these distances only to within a few percent. If your cluster is 5000 ly away, you know where yo are to maybe 200 ly.
I´m not particularly confident of either uniqueness or detectability.Chronos said:The pioneer gold album used pulsars. If its good enough for NASA its good enough for me. Since pulsars have a unique signature and are detectable at long distances, they should be adequate for locating just about any position relative to the sun within the MW galaxy
Chronos said:See http://arxiv.org/abs/0905.4121, Using pulsars to define space-time coordinates, for discussion. It is claimed millisecond pulsars could be used to locate any object in the galaxy within a meter.
Break off the recording for a while, and you have no idea which specific millisecond cycle you are observing.[PLAIN]http://arxiv.org/abs/0905.4121 said:It[/PLAIN] would not be sufficient to e-mail this arXiv posting to the Pluto colony in order for them to be able to use these coordinates: one vessel must have traveled from the Earth to Pluto, continuously recording the pulsar signals, so the origin of the coordinates would have been ‘transported’ to Pluto. Only then, the Pluto colony would share a common coordinate system with the mainland.
Travel just a thousand lightyears away from Taurus, and Crab pulsar does not exist, because you are looking at times before the Crab supernova.Chronos said:Since pulsar periods are unique
?snorkack said:Travel just a thousand lightyears away from Taurus, and Crab pulsar does not exist, because you are looking at times before the Crab supernova.
What he means is this: The supernova that formed the Crab Nebula and its pulsar was seen on Earth in 1054 AD or 961 years ago. So, if you were 1000 light years from the Earth in the opposite direction from the Crab nebula, the light from that supernova would not have arrived yet. In other words, neither the nebula nor the pulsar would be visible yet in the sky for an observer in this part of the galaxy, just the star that would eventually become the pulsar.Chronos said:?
My inclination would be to not use radio band. In visible light, decent angles can be measured by using eye lens.Vanadium 50 said:There are several problems with using pulsars. One is that they are directional - you might not see the ones you want. Another is that they are variable - apart from not even existing when you get far enough away, their periods change over time, and do so as a mix of a continual acceleration and sudden accelerations. Over thousands of years (which equals thousands of light years) their periods become an unreliable means of identification. Finally, to get good angular resolution requires a very large dish or set of dishes.
So you probably need to find some way to get in the rough (1000 ly?) ballpark before this technque even starts to work. Also, my inclination would be not to use the angles at all - because it's unlikely I brought aboard some giant dishes.
I see this as a bad approach. Can you, first, identify them?Vanadium 50 said:Instead I'd just look at periods: I'd measure the pulsar periods, compare with the known periods, and move in one direction until the chi-squared is minimized, Then I'd go on a perpendicular trajectory and minimize the Chi-squared again.
On average, you are not seeing any supernova most of time. As for supernova progenitors, they are relatively inconspicuous.Vanadium 50 said:Which gave me an idea. Look at the LMC. Do you see the SN1987a progenitor or not? Move radially with respect to the LMC until you have found the spot where you see the supernova. You know the Earth is on a sphere centered on the LMC, but 28 light years closer. If you wish, you can improve your knowledge of the location of the sphere by repeating this at widely separated places. Now, there are maybe a dozen or two supernovae where we know the progenitor stars. Repeat this with them. One supernova gets you the surface of a sphere. Two gets you a circle. Three gives you two points (most likely only one is in the galactic plane). Four gives you a point and a chi-squared. After about a half dozen, you will know the position of Earth to within about a light-day.
Yeah the OP postulates this at the beginning, although I don't think he is assuming that traveling through wormholes realistically is possible.Chronos said:So how do you get there from Earth before that light arrives - wormhole?
snorkack said:As for supernova progenitors, they are relatively inconspicuous.
KenNKC said:Assuming the crew possesses all of our current knowledge...
Vanadium 50 said:As I said, there are a dozen or two that are known. You don't have to say "Hmmm...is that a progenitor or not?" You can ask "Do I see this particular star or not?" And remember, every known progenitor was found in a survey. (For obvious reasons)
No. Many of them are in poorly known places outside a deep sky object. The rest are in deep sky objects, but in poorly known places within.Vanadium 50 said:Since the precursors are all in known places in known deep-sky objects, there is no problem identifying them.
snorkack said:No. Many of them are in poorly known places outside a deep sky object. The rest are in deep sky objects, but in poorly known places within.
Yes - that's part of the premise in the starting post.Chronos said:So how do you get there from Earth before that light arrives - wormhole?
The starting post doesn't specify.Nugatory said:Yes - that's part of the premise in the starting post.
KenNKC said:Let's say a spaceship from Earth (via a wormhole or something) suddenly found itself in a random place in the Milky Way galaxy. Assuming the crew possesses all of our current knowledge of the galaxy, and time was not a factor, would they be able to locate where our Sun is, and travel back to it?
Draygoes said:You would need support from the Earth for this one. I say that for a reason... even if you could find your way back to our star, you would be stuck around a large number of planets, moons, and anything else that chooses to get in your pathway.
I think the "travel back to it" is a lot more challenging than locating where you are. Even if "time was not a factor", propulsing yourself back to sol with current technology would be daunting. Your random place in the galaxy is likely to be over 40,000 light years away. If time is not a factor, then we are not worrying about aging the crew, aging the ship, or aging our solar system and its civilizations. But you still have a current-technology craft that will need to be fueled and perhaps refueled.KenNKC said:Assuming the crew possesses all of our current knowledge of the galaxy, and time was not a factor, would they be able to locate where our Sun is, and travel back to it?
