When I see depictions of the Milky Way it appears that the objects within it move counter-clockwise. Is this accurate? If so, do all spiral galaxies spin in this direction and why?
The direction that the Milky Way spins depends on your perspective. For example, take a top and spin it clockwise on a glass table. Then look at the spinning top from below the glass table - it will appear to spin counter-clockwise now. Or similarly, draw an arrow on a piece of paper in the clockwise direction, then hold the paper up to a light, looking at it from the bottom - now the arrow goes in the counter-clockwise direction. Thus the direction of the spin of any galaxy depends on your perspective when you look at it.
Scientists believe that on large scales the Universe is isotropic (the same in all directions). Thus, from our perspective, half of all spiral galaxies should spin clockwise, and half counter-clockwise. A recent analysis of the spin of spiral galaxies confirms this. The public classified over 35,000 spiral galaxies with spins both clockwise and counter-clockwise in the Sloan Digital Sky Survey as part of the Galaxy Zoo project. Scientists published the results in a recent paper and found that the Universe is indeed isotropic - we see the same number of clockwise as counter-clockwise spirals (within the uncertainties).
This page was last updated on June 27, 2015