Lunar eclipses have always been a topic of interest throughout history and many civilisations have strived to try and find out how and why lunar eclipses occur as well as the frequency in which they occur. This is because of how mysterious and beautiful a lunar eclipse looks, especially in past civilisations. A lunar eclipse is said to occur when the moon passes behind the earth and because of this the sun’s rays do not reach the moon because of it being blocked by the earth. This can only happen when the Sun, Moon, and the Earth are aligned together or very close together.
This diagram clearly shows the formation of lunar eclipses and how they occur. The umbra is the darkest part of the earth’s shadow while the penumbra is the lighter part of the earth’s shadow. This confirms that for a lunar eclipse to occur the planets must be aligned and that depending on the position of the moon a certain eclipse will happen. There are multiple types of lunar eclipses which are shown in the table below:
First Contact | Beginning of the Penumbral Eclipse |
Second Contact | Beginning of the Partial Eclipse |
Third Contact | Beginning of the Total Eclipse |
Fourth Contact | End of the Total Eclipse |
Fifth Contact | End of the Partial Eclipse |
Sixth Contact | End of the Penumbral Eclipse |
As can be seen there are 3 types of eclipses. The penumbral eclipse happens when the moon enters the earth’s penumbra. The partial eclipse happens when only part of the moon has entered the earth’s umbra. The total eclipse happens when the moon has travelled completely into the earth’s umbra.
This picture above shows how the colour of moon changes as it enters the different stages of the eclipse(Penumbral to Partial to Total and back again) and also how a total eclipse only occurs when a full moon is present.
Every year there are atleast 2 lunar eclipses with a maximum of 5 possible per year, however a total lunar eclipse doesnt happen very often. If you know the time a lunar eclipse will happen then you can use a Saros Cycle to predict when the next eclipse will happen.
The Saros Cycle is an eclipse cycle that states that when an eclipse occurs another almost identical eclipse will occur after 18 years and 11.3 days. This cycle can then be used to create a saros series which is multiple eclipses that have been predicted by the saros cycle and eventually this saros series will end as the eclipse differs greatly from the last, a new saros series will then begin.
So far it has been shown what our civilisation currently knows about lunar eclipses is great compared to past civilisations however they were still able to make correct predictions and findings. One of the first civilisations to manage to calculate when an eclipse would occur were the Chaldeans (1200 BC) using the Saros Cycle.
Eclipses back then were often seen as evil omens by the Greek’s who would make predictions about what would happen in the world based on the eclipse. Making predictions based on eclipses made sense to them as they didn’t have as much information about the world as we have so they had to make educated guesses about it. The Greek’s also managed to explain why an eclipse happens. Thales (620 – 546 BC) realised that the stars, moon and the sun were all solids. He also found that the moon was lit by the sun which explains why a lunar eclipse happens because of the earth blocking the sun’s light from reaching the moon. The Greek’s also were able to predict when a lunar eclipse would occur just as the Chaldeans had done using the Saros Cycle however they called it something different.
To conclude lunar eclipses are beautiful and have always been a large topic of interest. A lunar eclipse occurs when the Sun, Earth and the Moon are aligned together while the earth blocks the Sun’s light from reaching the moon. There are 3 types of lunar eclipses which are called Penumbral eclipses, Partial eclipses and Total eclipses. Each have different conditions for them to happen and a total eclipse can only take place when the full moon is present. Also there are around 2-5 eclipses every year but total eclipses occur very rarely. A lunar eclipse can be predicted using the Saros Cycle early civilisations such as the Greek’s used the Saros Cycle to predict the time of eclipses and also were able to explain why lunar eclipses happen which is a great feat.
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