The Curious Case of Venus-Moon Conjunction

A fellow U.P. Astrosoc member asked this question:

“I just noticed…everytime there’s a conjunction of the Moon and Venus, they are always in their crescent phase… is it always like that?:D” -Kathy

I find this question interesting and will try to answer based on my past observations of planetary conjunctions. (You may visit UP Astrosoc’s Facebook fan page to read my answer in Filipino.)

Planet Venus  is the brightest starlike object in the sky visible near or before dawn, near dusk and early evening at certain times of the year.  Thus, it is called Morning and Evening star. The planet’s nearer orbit to the Sun is the reason why this happens. As for the moon, when it reaches its waxing crescent phase, you will only see it in the west  a few minutes after sunset and early evening before it sets.  The moon is visible before or near dawn in the east as it progresses to waning crescent phase.

The fact that the moon’s crescent phase coincides with the visibility of Venus at dusk and dawn may well be the reason why the moon is always in its crescent phase during a conjunction between Moon and Venus.

I’m not sure in the case of Venus where it is also in its crescent phase. Venus was in gibbous phase last May 16 Venus-Moon conjunction and occultation.

What do you think? If you have a better explanation of this phenomenon, please comment on this post. 🙂

For more questions on a particular topic in astronomy, visit U.P. Astrosoc’s Ask an Amateur Astronomer to be enlightened!

To the stars!


~ by Stella's Gaze on June 25, 2010.

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