EJS Spiral Nebula Rotation Model is a approach to spiral nebulae. This simulation illustrates Adrian van Maanen's method for measuring the rotations (or internal motions) of spiral nebulae. Van Maanen used a device called a "blink stereocomparator" that allowed him to rapidly switch between viewing one image of a spiral nebula and another image of the same nebula taken at a later date. After aligning the foreground stars (which were not part of the nebula) in the two images, van Maanen made measurements of the displacements of various points in the nebula from one image to the other. His measurements indicated a noticeable rotation in several spiral nebulae, and these results were used to argue against the theory that spiral nebulae are separate galaxies (because if they were, then they must be so large and so distant that any rotations would be totally undetectable in the span of time between the two images used by van Maanen). Later, Edwin Hubble showed that van Maanen's analysis was flawed and that the rotations he had measured were not real. By that time most astronomers had already come to accept that spiral nebulae are separate galaxies.

Requirements:
* Java

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