C/1999 T1 (McNaught–Hartley)

C/1999 T1 (McNaught–Hartley) is a non-periodic comet discovered independently by Robert H. McNaught and Malcolm Hartley in 1999. Its designation indicates that it is a comet (C/) discovered in 1999 (1999), in the 20th half-month of the year (T), and was the first such object discovered in that half-month (1). McNaught and Hartley made their respective discoveries using the Schmidt telescope at Siding Spring Observatory in Australia.

The comet's orbit is highly eccentric, characteristic of long-period comets originating from the Oort cloud. Orbital calculations based on observed positions suggest a period of thousands of years, meaning it will not return to the inner solar system for a very long time.

Observations of C/1999 T1 (McNaught–Hartley) provided valuable data for studying the composition and behavior of cometary nuclei and comas as it approached the Sun. Spectroscopic analysis likely revealed information about the comet's volatile compounds and dust particles.

The comet's brightness peaked during its perihelion passage, allowing astronomers to study its activity and interactions with the solar wind and radiation. As with many comets, its brightness varied depending on factors such as its distance from the Sun and Earth, and its outgassing rate.