The ornamental design for a nighttimeskyviewing apparatus, as shown and described.
FIG. 1 is a front view of the nighttime sky viewing apparatus.
FIG. 2 is a rear view of the claimed design.
FIG. 3 is a side view of the claimed design.
FIG. 4 is a top side view of the claimed design.
FIG. 5 is a bottom view of the claimed design; and,
FIG. 6 is an isometric view of the claimed design in use with environmental matter that is not being claimed, but which is being depicted in dashed lines.