How to determine the moon phase like 🌑🌒🌓🌔🌕🌖🌗🌘 ?

[gongzhang]

I'm still not quite sure how I should get the moon phase after reading https://github.com/onekiloparsec/SwiftAA/issues/63. 😂

The goal is to determine the current moon phase like: 🌑 🌒 🌓 🌔 🌕 🌖 🌗 🌘 . As I understand it, I need both Moon.phaseAngle and Moon.positionAngleOfTheBrightLimb information to draw the icon.

   phaseAngle  positionAngleOfTheBrightLimb

🌑   180°        ~ 260°
🌒   135           .
🌓   90°           .
🌔   45          ~ 290°
🌕   0           ~ 90°
🌖   45            .
🌗   90°           .
🌘   135           .
🌑   180°        ~ 80°

The Moon.phaseAngle is straightforward. However, how should I determine whether the left or right side of the moon is bright based on Moon.positionAngleOfTheBrightLimb? Also, this seems to assume that we all observe the moon from the northern hemisphere. Am I right?

[HerrAlien]

I'd use selenographicPositionOfTheSun() instead of positionAngleOfTheBrightLimb () , and examine the longitude.

Regards, Alex

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On Tue, May 11, 2021 at 7:34 PM Gong Zhang @.***> wrote:

I'm still not quite sure how I should get the moon phase after reading #63 https://github.com/onekiloparsec/SwiftAA/issues/63. 😂

The goal is to determine the current moon phase like: 🌑 🌒 🌓 🌔 🌕 🌖 🌗 🌘 . As I understand it, I need both Moon.phaseAngle and Moon.positionAngleOfTheBrightLimb information to draw the icon.

phaseAngle positionAngleOfTheBrightLimb

🌑 180° ~ 260°

🌒 135 .

🌓 90° .

🌔 45 ~ 290°

🌕 0 ~ 90°

🌖 45 .

🌗 90° .

🌘 135 .

🌑 180° ~ 80°

The Moon.phaseAngle is straightforward. However, how should I determine whether the left or right side of the moon is bright based on Moon.positionAngleOfTheBrightLimb? Also, this seems to assume that we all observe the moon from the northern hemisphere. Am I right?

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[gongzhang]

@HerrAlien Thanks! 👍