The Moon Now

Moon Phases 2019

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Moon Phases for Amsterdam, Netherlands in 2019

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Moon Phases Explained 

It takes our Moon about 29.5 days to completely cycle through all eight phases. Occasionally (about every 2.7 years) there are two Full Moons in the same month. This is referred to as a Blue Moon. Hence the saying

"Once in a Blue Moon".

New Moon

The side of the moon facing the Earth is not illuminated. Additionally, the moon is up through out the day, and down through out the night. For these reasons we can not see the moon during this phase.

Waxing Crescent

During this phase, part of the Moon is beginning to show. This lunar sliver can be seen each evening for a few minutes just after sunset. We say that the Moon is "waxing" because each night a little bit more is visible for a little bit longer.

First Quarter

During first quarter, 1/2 of the moon is visible for the first half of the evening, and then goes down, leaving the sky very dark.

Waxing Gibbous

When most of the Moon is visible we say it is a Gibbous Moon. Observers can see all but a little sliver of the moon. During this phase, the Moon remains in the sky most of the night.

Full Moon

When we can observe the entire face of the moon, we call it a Full Moon. A full moon will rise just as the evening begins, and will set about the time morning is ushered in.

Waning Gibbous

Like the Waxing Gibbous Moon, during this phase, we can see all but a sliver of the Moon. The difference is that instead of seeing more of the Moon each night, we begin to see less and less of the Moon each night. This is what the word "waning" means.

Last Quarter

During a Last Quarter Moon we can see exactly 1/2 of the Moon's lighted surface.

Waning Crescent

Finally, during a Waning Crescent Moon, observers on Earth can only see a small sliver of the Moon, and only just before morning. Each night less of the Moon is visible for less time.

Effect of parallax !!!
The Earth subtends an angle of about two degrees, when seen from the Moon. This means that an observer on Earth who sees the Moon when it is close to the eastern horizon sees it from an angle that is about two degrees different from the line of sight of an observer who sees the Moon on the western horizon. The Moon moves about 12 degrees around its orbit per day, so, if these observers were stationary, they would see the phases of the Moon at times that differ by about one-sixth of a day, or four hours. But in reality the observers are on the surface of the rotating Earth, so someone who sees the Moon on the eastern horizon at one moment sees it on the western horizon about 12 hours later. This adds an oscillation to the apparent progression of the lunar phases. They appear to occur more slowly when the Moon is high in the sky than when it is below the horizon. The Moon appears to move jerkily, and the phases do the same. The amplitude of this oscillation is never more than about four hours, which is a small fraction of a month. It does not have any obvious effect on the appearance of the Moon. However, it does affect accurate calculations of the times of lunar phases.

https://en.wikipedia.org/wiki/Parallax

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