When Lilacs Last in the Dooryard Bloom'd Whitman's encounter with the lilacs in bloom in his mother's yard caused the flowers to become "viscerally bound to the memory of Lincoln's death". According to Gregory Eiselein: In the weeks before Lincoln's assassination, Whitman observed the planet Venus shining brightly in the evening sky. He later wrote of the observation, "Nor earth nor sky ever knew spectacles of superber beauty than some of the nights lately here. The western star, Venus, in the earlier hours of evening, has never been so large, so clear; it seems as if it told something, as if it held rapport indulgent with humanity,
Stability of the Solar System essentially the distance from sun to earth). These are now known as the Kirkwood gaps. Some asteroids were later discovered to orbit in these gaps, but their orbits are unstable and they will eventually break out of the resonance due to close encounters with a major planet. Another common form of resonance in the Solar System is spin–orbit resonance, where the period of spin (the time it takes the planet or moon to rotate once about its axis) has a simple numerical relationship with its orbital period. An example is our own Moon, which is in a 1:1 spin–orbit resonance