The phases of the Moon
The Moon revolves around the Earth and the earth revolves around the sun. The plane of moon orbit is inclined at an angle of 5 degree to the plane of earth orbit around the sun.The alignment of the moon and the sun determines the phases of the Moon. Let us see the different phases of the moon during the lunar month.The moon takes exactly 29.53 days (29 days 12 hours 44 minutes and 2.9 seconds) to complete one revolution around the earth.
Note: The moon orbit plane around the earth is half time up and half time down to the earth orbit plane around the sun.
Phase 1- New Moon
In this phase, the moon is in between the Sun and the Earth, but not in a perfect straight line, because the moon’s orbit plane is inclined by 5 degrees to the earth orbit plane around the sun. At the new moon therefore the moon does not block the sun completely. The bright side of the Moon faces away from the Earth and its dark side facing toward the earth therefore not visible to viewers on earth. The brilliance of the sun also affects visibility.
Phase 2- Waxing Crescent
Waxing means getting bigger. In this phase the moon is getting bigger and is less than 1/2 illuminated by direct sunlight.
Phase 3- First Quarter
The right half of the Moon is illuminated and the left side of the Moon is dark. The part of the Moon that appears lighted gets bigger and bigger as it revolves around the earth.
Phase 4- Waxing Gibbous
The moon is more than 1/2 illuminated by the sun and the moon’s illumination is getting bigger until the size of the moon.
Phase 5- Full Moon
In this phase, the Earth is in between the sun and moon but not in a perfect straight line as like the case in the new moon, because the moon orbit plane is inclined by 5 degrees to the earth orbit plane around the sun.The side of the moon that is illuminated by the sun is facing the earth. The entire moon is visible at this point.
Phase 6- Waning Gibbous
Waning means getting smaller. The moon is more than 1/2 illuminated and the moon’s illumination is getting smaller
Phase 7- Last Quarter
The left half of the moon appears lighted, and the right side of the moon appears dark .The illuminated part of the moon that we can see is slowly getting smaller and smaller until the New Moon.
Phase 8- Waning Crescent
A small part of the moon is illuminated at this point and the moon’s illumination is decreasing.The crescent will grow smaller and smaller every day, until the moon looks like the New moon.
Note: If the moon’s tilt instead of 5 degree was 0 degree, then we would have total solar and lunar eclipses every month.
Zia Ahmed Khan
email: khanziaahmed50@gmail.com
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