How did scientists observe Halley’s Comet during its 1986 appearance?

During its 1986 appearance, scientists observed Halley’s Comet using both ground-based telescopes and interplanetary spacecraft.

Astronomers first imaged the comet in October 1982 using the Hale Telescope at Palomar Observatory while it was still beyond the orbit of Saturn.1

In March 1986, five spacecraft conducted close-range investigations:
* Giotto: A European Space Agency probe that passed within 596 km of the nucleus, providing vivid images and data confirming the comet was a "dirty snowball" composed of water ice, silicates, and organic dust.21
* Vega 1 and 2: Two Soviet probes that provided data helping controllers guide the Giotto mission.21
* Sakigake and Suisei: Two Japanese spacecraft that also flew past the comet.1

These missions confirmed the nucleus was a solid body with a dark, crusty surface, effectively disproving the "sandbank model" that suggested the comet was merely a cloud of dust.1