Waxing or waning?

This is about how to differentiate the waxing moon from the waning moon in the sky. »Waxing« is known to be the lunar phase between the new moon and the full moon (meaning the time when the crescent increases in size), whereas »waning« is known to be the lunar phase between the full moon and the new moon (the time when the crescent decreases in size). In order to remember on which side the curve is, here are some neat mnemonics.

A well-known example in English for the waxing moon is to use the spelling of the lower case letter »b«, which has a curve on the right hand side and therefore signifies »beginning«. For the waning moon, the »d« is used which has its curve on the left hand side, representing »descending«.

• ☽ = »b« = beginning (waxing)
• ☾ = »d« = descending (waning)

Another mnemonic describes the order of the waxing crescent → full moon → waning crescent, uses the shape of letters too, in this case the »D« and the »C« and creates the abbreviation »DOC«:

• ☽ = »D« = waxing moon
• O = »O« = full moon
• ☾ = »C« = waning moon

These mentioned mnemonics only work in this way in the northern hemisphere of the Earth. For the southern hemisphere you have to reverse the mnemonics (so to say »to turn them topsy-turvy«), because there, the curve of the moon is just the opposite for the observer.

Column: Worth reading, Worth seeing | 32 comments | Leave a comment
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Comments

  • thank you for share!

  • It’s also very easy to remember.

  • Very helpful blog. That is a cool trick.

  • the waxing that means it is massive moon

    • you are sad why

    • the moon waning that means shrinking

  • I am sad

  • the moon

  • thxs for helping!

  • In France, the letter C for “croître” (to grow) is used when the Moon is waxing, and the letter D for “décroître” (to reduce) when the Moon wanes.

  • A few weeks ago (late Dec. 2013), I observed what looked like a smile-crescent moon in The southwestern United States — so it was neither a “D” nor a “C” (but more of a shallow “U”); and I was very surprised to see the moon filling in “from the bottom up” — ? ? ? ! I wouldn’t be able to tell which it was (waxing/waning) from the mnemonics. Love your Blog, though.

  • What if the moon is less full on the top? Is it waxing or waning?

    • That depends on the position of the observer on Earth (southern or northern hemisphere). You have to decide if the reduction of the circle is slightly on the left side or the right side of the top. On the northern hemisphere a reduction on the top left side would mean “waxing”, on the top right side “waning”. On the southern hemisphere it is reversed.

  • thanks for helping me with me report

  • Actually, the moon phases are “reversed” in the Southern Hemisphere.

    • Exactly – that’s what we have described in the last paragraph. ;-)

  • This was very helpful. I’m wondering how many nights it takes from the beginning of waxing to the full moon; and how many nights of waning until moon is gone until it comes the next month. I LOVE every full moon; and can always see ‘the man in the moon.’
    Does the moon have a different side that shows in Europe, for example? Do they see ‘the man’ as we see him here?
    When we were in France several years ago, I didn’t see ‘him’ very clearly; so have been wondering if I was seeing another side of the moon from what I see here in USA? Thanks, Ginny

  • very useful

  • this has been of great benefit to me, because I can now differentiate between waning and waxing as used in the phases of the moon.

  • this helped me soo o much I’m taking a test on this tomorrow and I’m not going to fail anymore

  • What is the best way to let go of your negative around you during the waning of the moon

  • Les stroud spoke of it on one of his Norwegian mountain shows now I know I know thanks

  • Les stroud spoke of it in his Norwegian mountain shows now I know thanks

  • cool thanks

  • thnx it helped aaalllooottt

  • In Slovak we have a similar mnemonic too. Waxing moon is D as in “Dopĺňa sa” (filling in) and waning is C as in “Cúva” (backing up).

    I never knew that on the southern hemisphere it is reversed though. Thanks :)

    • That is great – thank you for this interesting information!

  • GREAT WAY TO REMEMBER THE DIFFERENCE BETWEEN THE WAXING & WANING OF THE MOON. VERY CLEVER. THANKS…I WILL ALWAYS REMEMBER NOW.

  • Thxs! Very helpful!

  • Thank you for the info.

  • Good to know I had been wondering about this a few days ago

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