Earth & climate
Earth, Moon & Sun
How Earth, Moon and Sun work together and how eclipses and the tides come about.
In the sky we see the Sun every day and the Moon on many nights. The three bodies Earth, Moon and Sun together form a finely tuned system. The Earth the Sun, the Moon orbits the Earth. From this dance amazing things arise: the phases of the Moon, rare eclipses and even the in the sea.
Who orbits whom
The Sun is a huge star and the centre of our solar system. The Earth needs a whole year to travel around the Sun once. The Moon is much smaller and circles the Earth in just over 27 days. From one full moon to the next it takes a little longer, about 29 days, because by then the Earth has itself moved on a bit around the Sun. The Moon does not shine by itself, it only reflects sunlight back to us. That is why we always see only the part of the Moon that is lit by the Sun at that moment. When the Moon stands exactly opposite the Sun, we look straight at its lit half, that is full moon. When it stands towards the Sun, it turns almost only its dark half to us, that is new moon. All the other phases of the Moon lie in between.
When a shadow falls
Sometimes the three line up exactly. When the Moon moves in front of the Sun, it goes dark for a few minutes in the middle of the day, though only in a narrow strip of the Earth: that is a . When instead the Earth moves between Sun and Moon, its shadow falls on the Moon and it turns reddish: that is a . It can be watched from the whole night side of the Earth. Both events are rare because the Moon's path is slightly tilted against the Earth's path. Usually the Moon passes just above or just below the Sun.
The Moon pulls at the sea
With its the Moon pulls very slightly at the Earth, especially at the water of the seas. On the side facing the Moon the water piles up into a bulge, and a second such bulge forms on the opposite side. Because the Earth turns once under these two bulges in a day, every coastal place usually gets high tide twice and low tide twice in between. So we notice the interplay of Earth and Moon very directly at the beach.
The moon pulls the water into two bulges, one facing it and one on the far side. Because Earth rotates beneath both, high tide comes about twice a day. At full and new moon the sun pulls the same way: spring tide.
Exercises
0 of 6 solvedTime to try it yourself. You can't break anything, every attempt counts.
Why can we see the Moon in the sky?
What happens during a solar eclipse?
The Moon needs about 27 days for one lap around the Earth. How many days is that for 2 full laps?
Match each sky event to what happens during it.
At a coastal place there is high tide 2 times a day. How often is that in a week of 7 days?
The Moon does not shine by itself, it only reflects the … back to us.