Colliding galaxies. Combined infrared and optical image of two colliding spiral galaxies, NGC 2207 (left) and IC 2163 (right). The optical parts of this image (blue/green, hot young stars and galactic centres) were imaged with the Hubble Space Telescope (HST). The cooler, infrared- emitting regions (red, dust in the spiral arms) were imaged with the Spitzer Space Telescope (SST). Both the HST and SST are telescopes in Earth orbit. These galaxies began colliding 40 million years ago, and will take millions more years to finally merge. They are some 140 million light years from Earth, in the constellation of Canis Major.