The Moon appears as a thin crescent when it is close to solar conjunction, which is better known as new moon.
An object is said to be at solar conjunction when it makes its closest approach to the Sun in the sky.
The planets are typically lost in the Sun's glare and impossible to observe for a few weeks when they pass solar conjunction. Mercury can reappear within only a few days, since it moves around its orbit so quickly that it can pass from solar conjunction to maximum elongation in less than a month.
List of solar conjunctions
The table below lists the dates when objects are at solar conjunction in 2019, computed from NASA's DE405 planetary ephemeris. To show dates in other years, use the dropdown control.