Monday, 21 January 2019

Moon

The Moon is a funny customer. Its weight is 1.23% of Earth and it revolves round us in 27 days, 7 hours, 43 minutes and 11.5 seconds. It originated about 4.5 billion years ago, not long after Earth, and always turns the same face towards us. Its distance to the center of Earth varies between roughly 350,000 and 400,000 kilometers. 

Due to its gravity forces the Moon is the prime mover of marine tides on our planet, so I have experienced the Moon’s influence for a large part of my life. In the past we occasionally used the Moon in celestial navigation at sea. Occasionally, because the arithmetic involved is more complex.

Movement
When you look at the sky, you see the Moon tracing its way more slowly from east to west than the Sun. Starting from a new Moon, it drops behind day by day and after a little over 13 days it stands right opposite the Sun - a full Moon.

But unlike the Sun, which travels a neat course through the sky and reaches its highest and lowest position every summer and winter, the Moon staggers over the expanse
like a drunken sailor. In two weeks time, the largest angle it makes with the equator changes from north to south or vice versa. Now it is almost above your head, then again low above the horizon.

Phases
Depending on the light of the Sun shining on the Moon we see it either as a full moon, a part moon or not at all. When the Moon is facing the Sun, it is full. When it is almost in line with the Sun, we can hardly see it (new moon). So when the Sun sets and the Moon rises on the opposite side at the same time, it is full. If it sets shortly after the Sun, we hardly see it, apart perhaps from a narrow sickle.

Lunar eclipse
Earth casts a shadow cone in space, which the Moon passes through occasionally due to its apparently erratic course. The shadow of Earth on the Moon obscures the light of the Sun. Now it is full, and a while later it has partly or completely gone. The last complete lunar eclipse was early this morning, January 21, 2019. I filmed it.


The reddish sheen is due to the red light from the Sun being deflected in Earth's atmosphere and striking the Moon's surface.

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