This beautiful spiral galaxy reminds us of what our own Milky Way galaxy might look like if we were able to rise up out of its disk and look down from above. The thick spiral arms trace out a wave of star birth that sweeps around the galaxy and is kept in motion by the gravitational pull of billions of stars moving in close orbital synchrony. The regions of star birth contain massive blue-hot stars that shine brilliantly and illuminate the surrounding clouds of gas and dust, enhancing the visibility of the spiral arms.
This particular galaxy played a key role in a project that was completed in 1999 to establish an accurate extragalactic distance scale. Since it is relatively close by - a mere 25 million light years - individual Cepheid variable stars lying within the galaxy can be studied by the Hubble Space Telescope. This unusual kind of star provides a way to measure an accurate distance to the galaxy, and by obtaining accurate distances to a number of these "calibrator galaxies" other methods could then be used to establish the distances to yet more remote galaxies. Ultimately, these methods have provided a way to measure distances to all galaxies with an accuracy of about 7% - a huge improvement over the 50% uncertainty prior to the 1990s.