Mercury is defined as the line through its successive positions of perihelion and aphelion. Twain died on 21 April 1910, the day following the comet's subsequent perihelion. Pluto's visual apparent magnitude averages 15.1, brightening to 13.65 at perihelion. These orbital changes cause delays in its perihelion of four days, average. This discrepancy was the advance in the perihelion of Mercury of 42.98 arcseconds per century. Also, among currently known comets, there is a bias favoring those with short perihelion distances. Pluto's last passage through its perihelion was on 5 September 1989. When in opposition near its perihelion, Ceres can reach an apparent magnitude of +6.7. Einstein showed that general relativity agrees closely with the observed amount of perihelion shift. The anomalistic year is usually defined as the time between perihelion passages. As of its January 29, 2020, perihelion, the Parker Solar Probe's closest approach is . The perihelion dates of each apparition are shown. Every 15 to 17 years Mars comes into opposition near its perihelion. Science phases will run for a few days both before and after each perihelion. It was developed and published by Perihelion Software.