On January 29, Mars will reach opposition, a point along its orbit around the Sun where Mars will be directly opposite from the Sun in a two-planet and Sun line-up with the Earth in between. At this opposition, the Earth and Mars will be separated by nearly 100 million km. An opposition is similar to a full Moon in that the planet at opposition rises at sunset and sets at sunrise and is visible all night. An opposition can only occur between the Earth and the outer planets; at opposition, the outer planet is at its closest to the Earth.