The NASA JPL video What's Up: September 2019 Skywatching Tips from NASA says (per both the closed captions and audio):

We’re in a several-month period right now when the new Moon falls right around the end of each month. This means we get to enjoy lovely waning crescent moons at dusk for the first few days of each month, and delightful waxing crescents in the predawn sky near the end of each month.

  • Are "waning" and "waxing" used correctly here or is it just the opposite of what's said?
  • Would the video be correct if "waning" and "waxing" were replaced by "setting" and "rising"?

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1 Answer 1


I think they did make a mistake. The moon waxes after a new moon and wanes before a new moon. To wax means to grow bigger or stronger (and is cognate with "waist"!). To wane means to become smaller or weaker (cognate with "waste" and "vaccum").

The moon that sets shortly after sunset in the evening is a waxing moon. The moon that rises shortly before sunrise in the morning is a waning moon.


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