 The Chinese witnessed this supernova event in 185 AD, documenting a mysterious guest star that remained in the sky for eight months. This combined visible light and x-ray image shows the interstellar gas that has been heated to millions of degrees by the passage of the shockwave from the supernova. RCW 86 is approximately 85 light-years in diameter. If it were the star Capella, the shockwave would be tearing us apart right now.