Help!!!

[Jim C]

I'm in the process of writing an essay on the possibility of a cosmic impact having opened the Drake Passage. In the process of discovery I found 3 other cosmic impacts that happened in the same time frame. I tried to align these 4 locations on a map and they came out in a straight line giving me the impression that they may be part of the same progenitor. As I was getting some help in the layout of my data it was brought to my attention that the straight line was not possible on a globe and that I was tricked by the use of a Mecator map. What kind of a map would give me a picture of my 4 points and the likelihood of their alignment? I'm a rank amatuer at this sort of thing and can use any help I can get. Thanks for your time and expertise.

[Chick]

Plot them on a globe and then stretch a rubber band from first to last. The elasticity will make the rubber band follow a great circle, which is the nearest thing to a straight line on a sphere.

If your four points are aligned along a great circle, they would be in a straight line from a direction into space that is in the plane of the great circle.

[Jim C]

Thanks chick. I can see a trip to the library coming soon in my future. Is there any type of map that I can plug my location points onto and print a copy for my essay if they work out?

[Chick]

Thanks chick. I can see a trip to the library coming soon in my future. Is there any type of map that I can plug my location points onto and print a copy for my essay if they work out?

Once you find out where the great circle runs through them, you can plot that great circle on any projection you want. As Pixie says, a stereographic projection works as long as you center the projection on the line. A gnomonic projection also shows great circles as straight lines.

http://www.progonos.com/furuti/MapPr.../geodesic.html

You also might consider a photograph of the globe showing the rubber band

[Pixie]

I think that a stereographic projection will also let you find out if they fit in a straight line or not, since stereographic projections are for angle preservation... Hai-Etlik would be the expert to confirm/deny or expand on what I am saying...