Solar Conjunction
Solar conjunction generally occurs when a planet or other solar system object is on the opposite side of the Sun from the Earth. From an Earth reference, the Sun will pass between the Earth and the object. Communication with any spacecraft in solar conjunction will be severely limited due to the Sun's interference on radio transmissions from the spacecraft. The term can also refer to the passage of the line of sight to an interior planet or comet being very close to the solar disk. If the planet passes directly in front of the Sun, a solar transit occurs.
