Neptune's windy atmosphere in August 1989. The ice giant Neptune was the first planet located through mathematical predictions rather than through regular observations of the sky.
well slavery was an big issue because it separated the northern and southern states. the northern states realize that slavery was an unnessary inhumane treatment and wanted to abolished it. While the southern states depended on slaves since they worked for free on their plantation. To resolve this they counted 3 free men for 5 slaves until 1808.
The Missouri Compromise, as the first great Congressional compromise over the slavery issue, was also important as it set a precedent that Congress could regulate slavery in new territories and states. And that very issue would become a very important topic for debate decades later, especially in the 1850s.