Our moon Image source: Astronomynow.com Humans have been fascinated by the moon through time immemorial and it has had a huge impact on our society and culture – mythology, arts, calendar, and so on. The world of Literature has used the moon to compare so many things, especially poets who describe the beauty of a woman’s face by comparing it to the full moon. (My face definitely resembles the moon – full of craters and mountains as a result of pimples during teenage ) Perhaps some gourmands where very hungry when they looked at the full moon one day and imagined it to be cheese. Mothers have shown the moon to kids narrating stories and singing songs and also to get some kids to open their mouth to take food. Many remember terrace meals of curd rice roundels with a dollop of spicy kuzhambu on full moon days. Our moon was always called “The Moon” because we did not know that other moons existed until Galileo Galilei discovered Jupiter’s moons in 1610. Size and distance of the Earth and the Moon. The moon is farther away from Earth than most people realize. The moon is an average of 384,400 kilometers away. That means 30 Earth-sized planets could fit in between Earth and the moon If Earth was the size of a basketball the moon would be the size of a tennis ball and would be about 7.2 meters away - that is 1.3 saree lengths away. Interesting facts about the moon The moon’s gravity is only one sixth as that of the earth. So we will weigh six times less than our weight on earth. A 100 kg person will weigh 16.5 kg on the moon. It is the fifth largest moon in the solar system. The moon rotates on its axis and revolves around the earth at the same rate. This phenomenon is known as synchronous rotation. Due to synchronous rotation only one side of the moon is visible from Earth at all times. The side that is not visible is known as the far side. Some refer to it as the “dark side”. During a "full moon," the hemisphere of the moon we can see from Earth is fully illuminated by the sun. On a "new moon" the far side of the moon has full sunlight, and the side facing Earth experiences night. The near side and far side of the moon Image courtesy: slate.com The changing day/night portion on the moon as it rotates around the earth appears as “waxing” and “waning” and are also known as the “phases”. The moon makes a complete orbit around Earth and completes one rotation in 27 Earth days. However, because the Earth is rotating on its axis as it orbits the sun, the moon appears to orbit us every 29 days. What will we see if we cut a wedge off the moon? Earth's moon has a core, mantle and crust. The moon's core is 240 kilometers in radius. The innermost part of the shell is liquid iron that is about 90 kilometers thick. Covering this liquid iron is a layer of partially molten iron that is 150 km thick. The mantle extends from the top of the partially molten layer to the bottom of the moon's crust. It is most likely made of minerals that contain magnesium, iron, silicon and oxygen. The crust has a thickness of 70 kilometers on the moon's near-side (facing us) hemisphere and 150 kilometers on the far-side. It is made of oxygen, silicon, magnesium, iron, calcium and aluminum, with small amounts of titanium, uranium, thorium, potassium and hydrogen. Long ago the moon had active volcanoes, but today they are all dormant and have not erupted for millions of years. Image courtesy : planetfacts.org Surface The surface of the moon is ridden with craters which are result of steady impacts from raining asteroids, meteoroids, and comets. These impacts occurred because the moon does not have an atmosphere to burn up the heavenly bodies. Over billions of years, these impacts have ground up the surface of the moon into fragments ranging from huge boulders to powder. This rubble pile is called the lunar regolith. Beneath is a region of fractured bedrock referred to as the megaregolith. The light areas of the moon are known as the highlands. The dark features, called maria (Latin for seas). These were filled with lava between 4.2 and 1.2 billion years ago. Moon daytime temperatures go up to about 127 degrees Celsius when in full sun, and the nights on the moon are utterly bitterly cold, about -173 degrees Celsius. The moon has a very weak magnetic field. Life on Moon To date the many missions to moon have not suggested that life existed on the moon any time since its formation. Water India’s Chandraayan, and NASA’s LCROSS missions have provided evidence that water exists on the Moon. Scientists are currently working on confirming this. It is possible that trips to the moon may be resumed to explore further. Atmosphere The moon has a very thin and weak atmosphere, called an exosphere. It does not provide any protection from the sun's radiation or impacts from meteoroids. ******************** How old is our moon and how was it formed. Our moon is slightly younger than our Earth about 100,000 million years maybe. While many theories exist regarding its origin the most popular and currently accepted theory is that the moon resulted when a Mars-like body (Theia) collided with young Earth. This is popularly known as the giant-impact hypothesis or the Theia impact. The resulting debris from both Earth and “Theia” coalesced to form the moon. At first the moon was hot and in molten state. Over 100 million years the surface cooled and crystallized. The lighter rocks floated upward and eventually formed the lunar crust. image courtesy: sites.google.com A Moonless Earth (Solon) Let us suppose “Theia” did not encounter Earth those billions of years ago and went on its way and no moon was formed. How would it be today? (Parents, teachers – put this question to your children and bring out their responses. Guaranteed to bring out brilliant imaginative responses – enjoy). The moonless Earth would be known as “Solon” Let's see: - We will not have any lessons on the moon in our science books (Good – one less thing to learn for exams) - We will not be able to call any one a lunatic, or loony. - We will not have “months” - The poets and writers will have to find other sources to compare beauty.On the serious side: - We will not have any eclipses. We all know that when the moon comes between the Earth and the Sun it causes solar eclipse and when the Earth throws its shadow on the moon, it causes lunar eclipse.- Nights will be very dark. Now, even on a “new moon” night if we are in an open area devoid of electrical lights we can still see a little. That is because the light reflected off the surface of the moon is so bright that it lends to the faint visibility. Whereas if there was no moon, we would not be able to see our own hand at night if we lifted. Really, truly, pitch dark. Though there will be starlight, it will not be sufficient for us to see.- We will not have high ocean tides. The tides will be about 1/3 high as a result of the pull by the Sun’s gravity. However, this effect will be too negligible. The surfers would not even know that there was a sport called “surfing”- The days on the Earth would be 6 – 12 hours. When the Earth was first formed it was spinning very rapidly. Yes, the moon, with its gravitational force had slowed the Earth’s spin considerably.- We would not have predictable weather. The moon keeps the Earth tilted on its axis which is the reason we have predictable weather. If not for the moon the Earth’s axis would tilt too far or not tilt at all. Our weather patterns would be much different.- We would not be safe. Our Moon is full of impact craters caused by meteorites. The Moon has been protecting us by taking the brunt of these impacts. Aha! While all the above is true none of them would matter to us. As a matter of fact I willnot be writing this post and you will not be reading it. That’s because – without our moon, We would not have existed at all!! Let’s explore why. Multiple factors contributed to the evolution of life on Earth. 1. Earth's tilt - weather & temperature: Scientists believe that the Theia impact tilted the Earth’s axis at 23.5 degrees and the gravity of the moon has helped the Earth to maintain it. It is this axis tilt that maintains optimum temperatures spread evenly throughout the Earth’s sphere throughout the year. Without the axis tilt Solon would have extreme weather or no weather. Some parts would be only hot and some parts would be only cold. 2. Spin rate of the Earth:The young Earth was spinning very fast - 6-10 hours per day. This would have created hurricane force winds all the time. Therefore any animals life that were created would have adapted to facing hurricane force winds and also have a biological clock to sleep only three to four hours every day. Their bodies, and brains would have developed very differently than the species that inhabit the Earth today. 3. Meteorite impacts. Without the Moon to shield, Solon might have taken on many huge meteor strikes which could have wiped away life. 4. The most important factor were the tides. When life first began to appear on Earth, the moon was about half the distance as it is today. Therefore its tidal pull on the oceans was very strong and the waves were quite high. Also the Earth was spinning much faster. High and very strong tidal waves would pound the rocks, pulverize bits and pieces and take the nutrients back in to the ocean. This constant pulling of the ocean waves and the churning enabled primordial life to be spread across the planet. This, combined with the nutrient rich soup pools, provided the most optimum environment for the primordial life to evolve. In Solon, the only tides would be from the Sun. Today Solon would have slowed down a bit and its days might have been 8 hours long. Different species of life may have evolved from the very hot, very cold, fast spinning, erratic weather patterns, nutrition lacking seas, and confined primordial life. So, we have to thank "Theia" for our presence today and learning about it ********** Our Moon is moving farther and farther away from us at the rate of 3.8 centimeters per year. As it does, Earth's own spin rate is slowing.The day is getting longer by about 0.002 seconds per century. ******************************** Information sources: SCIENTIFIC AMERICAN, Astrosociety.org, NASA, scienceinschool.org
Note: This was a very time consuming post. There was so much information and I could not include all in this article. I have left out many, such as the blue moon, moon's surface, view of earth from the moon, man on moon, etc. Please ask questions and hopefully we can cover many other aspects of our moon. Thank you.
That is an incredible amount of work. Very comprehensive! Thank you for the article. Adding these to my 8 year old's reading list.
@kkrish ditto to @Gauri03 post, already shared with my son. The present topic between us is the increased frequency of intense earthquakes and activity and the latest discovery of plate movement in Indian Ocean. Do share if you have come across more on these.
Thank you @Gauri03 . I am glad that a future space scientist will get to read this. That would be my best reward.
Thank you @Shanvy Very happy to hear that another budding scientist had read the post. Yes, my next topic is on Mother Earth! This is going to take little more time - The amount of information on our Earth is astounding. I will certainly focus on earthquakes. Thanks for the request - it makes it easy for me.
" The resulting debris from both Earth and “Theia” coalesced to form the moon. At first the moon was hot and in molten state " Did all the debris over a time became the moon ,or few debris over a time became the moon ? If all the debris of earth have formed the moon ! then definitely we might one day have a tiny earth which is now called a moon , i might be insane but Ma'am plz reply all the debris or only few of earth and theia ???? Want to know What was the earth like when theia collided with Solon ?
Hi @Madhumagie Once again good question. Do keep in mind that the "Theia impact" is only a hypothesis and at present the most accepted one. There is still no compelling evidence that this happened. Research is on going. It could be confirmed by your daughter one day. Another theory has begun to evolve that there was no Theia impact. According to this theory, after planets formed, there were still remaining debris. Those that were close to and revolving around our Earth coalesced to form the moon. So we really do not know if all the debris from the Theia impact became the moon, or if some of the debris was attracted back to earth, or if some of the debris just drifted out and joined the astreroid belt. Our Earth was very young only about 100,000 million years old when Theia hit; a ball of molten hot lava. More on this in my next post on Earth.
Dear OP, Iam also a big lover of space and astronomy and your articles are inspiring and easy to understand. That said,i would also like to add that,if moon is not there,then earth's rotation would not have been stable and would have got wobblier due to the gravitational pull of outer planets. So its quite correct that ancient people worshipped sun and moon as gods.Without them,we would not be here.
Thank you JGVR. Your point on other planets causing earth to wobble is quite interesting. Can you please share the article? Would like to know more. Yes, you are correct that Sun and Moon, and planets too, are worshipped by humans. Not sure if we would exist if any of the planets did not exist too.
