Comet Nishimura will reach perihelion (the closest point to the Sun in its orbit) on Sept. 18 and, if it isn’t broken up by the Sun’s energy, will then swing back around and head back out into the Solar System. In that case, it will be visible to observers in the Southern Hemisphere, where it will appear very low in the western sky at dusk through the end of September. Northern Hemisphere observers will likely lose sight of Comet Nishimura after Sept. 13.
Comet Nishimura is named after Hideo Nishimura of Japan, the amateur astronomer who discovered the comet on Aug. 12, 2023. It likely came from the Oort Cloud, a distant region of the Solar System.
Comets like this have green heads, but this color doesn’t extend to their tails. This is because the green color is caused by diatomic carbon, a highly reactive molecule that is created from the interaction between sunlight and organic matter on the comet’s head and then almost immediately destroyed again by the Sun’s energy before it can move far from the nucleus.