M51’s two prominent arms offer a readable map of stars, gas and dust. This Hubble view was taken in January 2005. Dark clouds, pink star-forming regions and blue star clusters mark different features along the arms, while the companion NGC 5195 appears nearby.
Trace one arm from the centre outward instead of treating the spiral as decoration. The companion is passing behind M51, according to ESA/Hubble’s account. Apparent contact in a flat image does not establish that two structures occupy the same depth.
Source/image: NASA, ESA, S. Beckwith (STScI), and The Hubble Heritage Team (STScI/AURA) · CC BY 4.0. Resized; colours retained.