Final answer:
Halley's Comet, last seen in 1986, has a roughly 75-year orbit and will be visible from Earth again in 2061. Its orbit can vary slightly due to the gravitational influence of other planets.
Step-by-step explanation:
If Halley's Comet was last seen from Earth in 1986, it will be visible again in the year 2061. This famous comet has been observed since 239 BCE and has a periodicity of approximately 74 to 79 years, though most recent calculations suggest an average orbital period of about 75.3 years. The comet's return can vary slightly due to gravitational perturbations caused by larger planets in our solar system, which can affect the comet's orbit.
The anticipation of Halley's return excites both professional and amateur astronomers, as it provides a rare opportunity to observe and study a well-known celestial object. In 1986, the comet was met with several spacecraft, giving scientists invaluable information about its composition and characteristics, fueling excitement for its return in 2061 when it will once again be a focal point of sky observations.