It was late evening of 16th May. Whole of India was still busy buying tons of gold in the name of Akshaya Tritiya madness. I got SMS from close friend of mine, A.P. Subramanya asking me to capture Moon and Venus on the Northwest sky immediately. I looked at the crescent moon. He was grinning brightly just above the bright Venus. Even though I did not get tripod that day, I used my car as support and used my newly acquired Canon EF 300mm f/2.8 L IS USM lens with Canon EF 2X II Extender on my Canon EOS 5D mark II thus making it a 600 MM lens which is good for Astro-photography.
Earlier in the day moon had passed directly in front of and occult (eclipse) the planet venus. Most locations in the occultation’s ground path was in full daylight, but from some locations — in particular from Sumatra to the Philippines — the occultation occurred after sunset. When the moon will completely hide Venus for a short while. Just before the occultation, Venus will appear so close to the Moon that it would well be mistaken as being inside the crescent. It may well have been a glorious sight such as this that inspired the crescent moon and star symbol that has come to represent the faith of Islam. But don’t expect to see the star (Venus at least in this case) really inside the crescent, which is impossible. Being farther from Earth than the Moon (currently more than 500 times farther), it is not possible for Venus to shine through the solid body of the moon.
The moon passes somewhere near Venus about once a month, but conditions for observing aren’t always favorable. However, what you haven’t ever seen is a mention of the quarter moon, or gibbous moon, or full moon passing near Venus. Why is it that only the crescent moon ever passes Venus?
That’s because Venus is inferior. No, I don’t mean that it is less valuable in any way. Used in this context, inferior means lower than. Venus is lower than the Earth relative to the sun. In other words, Venus is closer to the sun. Because of this, Venus never appears very far away from the sun in Earth’s sky. It oscillates back and forth from one side of the sun to the other, much like a race car moving from the left side to the right side of a circular track as we watch it from the stands. Thus, Venus sometimes appears in the evening twilight, and sometimes in the dawn twilight. The point is that it is never far from the sun. The farthest it can get from the sun (called an elongation) is slightly more than 47 degrees. So when the moon appears to pass Venus, it does so at about the same elongation from the sun. Since 47 and fewer degrees correspond to a crescent phase, only the crescent moon can appear to pass near Venus in the sky. The quarter moon is 90 degrees from the sun, and the full moon is 180 degrees, so you will never see those phases near Venus.
Mercury is an inferior planet as well, but its maximum elongation is only 28 degrees, so only a very thin crescent moon can ever appear near Mercury. On the other hand, Mars, Jupiter and Saturn are farther from the sun than Earth, making them superior. From time to time they can appear at any angle from the sun, and the quarter or full moon phases can pass near them (sometimes even occulting them).