|The following diagrams show the global visibility of the new crescent Moon over the first three days of the
lunation. These diagrams are based on the current model for predicting
the visibility of the crescent moon using the Yallop criterion described
in HMNAO Technical Note No. 69.
Within the area of purple diagonal striping (if shown), the new crescent moon cannot be seen as the instant of new moon has not yet
occurred. The moon sets before the Sun within the area of the peach-coloured shading (if shown). The unshaded area, F, indicates
the region from which the new crescent moon cannot be seen — the thickness of the crescent is too thin to be seen i.e. it is
beyond the Danjon limit. In the dark blue shaded area, E, the new
crescent moon is not visible with a telescope and in the pale blue shaded area, D, optical aid of some sort will be needed to see
the new crescent moon. In the pale yellow coloured area, C, you may need optical aid of some sort to find the new crescent moon
initially. In the yellow shaded area, B, the new crescent moon should be visible under excellent atmospheric conditions with the
naked eye and finally, in the red shaded area, A, the new crescent moon should be easily visible with the naked eye.
The near vertical curved lines labelled 0, 2, 4, 6 etc., show the
age of the moon in hours at the
"best time" of observation, defined in HMNAO Technical Note No. 69
as 4/9 of the time difference between sunset and
moonset or the time of sunset plus 4/9 of the
"lag time". The instant of new moon is given below the diagram.
The age of the moon at its first visibility with a telescope and also with the naked eye are given below the diagram where
appropriate. A key describing the annotation and shading is given beneath each diagram.
The following diagram shows the visibility of the new crescent Moon on 2021 May 11.