Heidi Hammel improvements to the adaptive optics systems of the Keck telescope, astronomers became able to capture "unbelievably crisp images" and view many details that could not be seen before. Hammel's planetary research with Hubble and Keck has demonstrated that both Uranus and Neptune are dynamic worlds. Hammel primarily studies the outer planets and their satellites, focusing on observational techniques. She was a member of the Imaging Science Team for the Voyager 2 encounter with the planet Neptune in 1989. In 1994, Hammel led the team that investigated Jupiter's visible wavelength response to the impact of comet Shoemaker-Levy 9 using the Hubble
Lexell's Comet The comet was also noted by several other astronomers. The comet was observed in Japan. Surviving records identify it as an astronomical and historical phenomenon. It was observed in the Hejaz in Safar 1184 AH (June 1770), where some believed it to be the comet predicted by the poet al-Fasi, portending future events. On July 1, 1770, the comet passed 0.015 astronomical units from Earth, or approximately 6 times the radius of the Moon's orbit. Charles Messier measured the coma as 2° 23' across, around four times the apparent angular size of the Moon. An English astronomer at the time