Editing Space Interferometry Mission (section)

===Galactic mapping===
[[Image:Milky Way 2005.jpg|thumb|left|How scientists think the Milky Way is shaped]]
Interferometric measurements of stellar positions over the course of the mission would have permitted SIM to precisely measure the distances between stars throughout the [[Milky Way]]. This would have allowed astronomers to create a "roadmap" of the Galaxy, answering many questions about its shape and size.<ref name=dark1>[http://planetquest.jpl.nasa.gov/SIM/simLiteScience/darkMatterGalaxies/ The Milky Way and Dark Matter] {{webarchive|url=https://web.archive.org/web/20100530064440/http://planetquest.jpl.nasa.gov/SIM/simLiteScience/darkMatterGalaxies/ |date=30 May 2010 }}, NASA, SIM Lite, Jet Propulsion Laboratory. Retrieved 9 March 2010.</ref><ref name=dark2>[http://planetquest.jpl.nasa.gov/SIM/scienceMotivations/darkMatter/ SIM Lite and Dark Matter] {{webarchive|url=https://web.archive.org/web/20100614193918/http://planetquest.jpl.nasa.gov/SIM/scienceMotivations/darkMatter/ |date=14 June 2010 }}, NASA, SIM Lite, Jet Propulsion Laboratory. Retrieved 9 March 2010.</ref>

Currently, astronomers know little about the shape and size of our galaxy relative to what they know about other galaxies; it is difficult to observe the entire Milky Way from the inside. A good analogy is trying to observe a marching band as a member of the band.<ref name=guide/> Observing other galaxies is much easier because humans are outside those galaxies. Steven Majewski and his team planned to use SIM Lite to help determine not only the shape and size of the Galaxy but also the distribution of its mass and the motion of its stars.<ref name=guide>Silberg, Bob. "[http://planetquest.jpl.nasa.gov/news/sim_guideToGalaxy.cfm Building a better guide to the Galaxy] {{webarchive|url=https://web.archive.org/web/20070509153845/http://planetquest.jpl.nasa.gov/news/sim_guideToGalaxy.cfm |date=9 May 2007 }}", NASA, SIM PlanetQuest, 14 February 2006, ''Jet Propulsion Laboratory''. Retrieved 24 April 2007.</ref>

SIM Lite measurements of Milky Way stars were to yield data to understand four topics: fundamental galactic parameters, the [[Oort Limit]], disk mass potential, and mass of the Galaxy to large [[radii]].<ref name=mainUVA>"[http://astsun.astro.virginia.edu/~rjp0i/takingmeasure/index.shtml Main Page] {{webarchive|url=https://web.archive.org/web/20070406221823/http://astsun.astro.virginia.edu/~rjp0i/takingmeasure/index.shtml |date=6 April 2007 }}", Taking Measure of the Milky Way: A SIM PlanetQuest Key Project, University of Virginia, site updated 1 June 2005. Retrieved 25 April 2007.</ref> The first, fundamental galactic parameters, was aimed at answering key questions about the size, shape and the rotation rate of the Milky Way.<ref name=parameters>"[http://astsun.astro.virginia.edu/~rjp0i/takingmeasure/keyproject1.shtml Fundamental Galactic Parameters] {{webarchive|url=https://web.archive.org/web/20070206060234/http://astsun.astro.virginia.edu/~rjp0i/takingmeasure/keyproject1.shtml |date=6 February 2007 }}", Taking Measure of the Milky Way: A SIM PlanetQuest Key Project, University of Virginia, site updated 1 June 2005. Retrieved 25 April 2007.</ref> The team hoped to more accurately determine the distance from the Sun to the [[Galactic Center]]. The second topic, the Oort Limit, would have attempted to determine the mass of the galactic disk.<ref name=oort>"[http://astsun.astro.virginia.edu/~rjp0i/takingmeasure/keyproject2.shtml Oort Limit] {{webarchive|url=https://web.archive.org/web/20070818102238/http://astsun.astro.virginia.edu/~rjp0i/takingmeasure/keyproject2.shtml |date=18 August 2007 }}", Taking Measure of the Milky Way: A SIM PlanetQuest Key Project, University of Virginia, site updated 1 June 2005. Retrieved 25 April 2007.</ref>

The third project topic was disk mass potential. This topic was designed to make measurements of the distances to disk stars as well as their proper motions. The results of the third topic of study were to be combined with the results of the fundamental galactic parameters portion of the study to determine the Solar System's position and velocity in the galaxy.<ref name=diskmass>"[http://www.astro.virginia.edu/~rjp0i/takingmeasure/keyproject3.shtml Disk Mass Potential] {{Webarchive|url=https://web.archive.org/web/20131103040752/http://www.astro.virginia.edu/~rjp0i/takingmeasure/keyproject3.shtml |date=3 November 2013 }}", Taking Measure of the Milky Way: A SIM PlanetQuest Key Project, University of Virginia, site updated 1 June 2005. Retrieved 25 April 2007.</ref> The final topic dealt with dark matter distribution in the Milky Way. SIM data was to be used to create a [[three-dimensional space|three-dimensional]] model of mass distribution in the Galaxy, out to a radius of 270 [[kiloparsec]]s (kps). Astronomers were to then use two different tests to determine the galactic potential at large radii.<ref name=radii>"[http://www.astro.virginia.edu/~rjp0i/takingmeasure/keyproject4.shtml Mass of the Galaxy to Large Radii] {{Webarchive|url=https://web.archive.org/web/20131103040529/http://www.astro.virginia.edu/~rjp0i/takingmeasure/keyproject4.shtml |date=3 November 2013 }}", Taking Measure of the Milky Way: A SIM PlanetQuest Key Project, University of Virginia, site updated 1 June 2005. Retrieved 25 April 2007.</ref>