The Moon, as seen through the Azim Premji University 200mm diameter Dobsonian reflecting telescope.

“Wow! There are so many craters!”, gasped the student while her eyes were glued to the eyepiece. It was a crisp moonlit night and dozens of students were gathered on the roof of one of the buildings on the Azim Premji University, Bengaluru campus, to explore the sky through the 200mm diameter Dobsonian telescope. The reaction of every student was equally wondrous, even though many had seen the Moon through a telescope several times before. 

The Moon is our closest celestial neighbour. It has had a deep impact on our imagination and a profound influence over our lives. Very literally. Life on Earth as we know it would not have been possible without the Moon. The tides, which occur due to the gravitational pull of the Moon, cause the waters of the seas and oceans to retreat and flood coastal lands twice daily. Life, which originated in the oceans, slowly adapted to land as amphibians due to this oscillating aquatic dance¹. It’s extremely unlikely that you and I would have been around without our Moon. The Moon also protects us by gravitationally deflecting asteroids from impacting the Earth. Many birds and insects use the Moon to migrate and navigate ². We clearly owe a lot to the Moon.

It would be fair to say that the Moon has captured our imagination more than any other celestial body in the universe. The first day of the week is the ​“day of the Moon”: Monday, Lundi, Montag, Somvara in several languages. The word ​‘month’, twelve of which make up our Gregorian year, is also derived from ​‘moon’, since the period of revolution of the Moon around the Earth is roughly the average length of a month. Civilisations across the world have developed and followed a lunar calendar and to this day many of our festivals are celebrated on dates associated with such a calendar. The various phases of the moon evoke varied human emotions, from fear of the darkness during a new Moon night to moonstruck romantic couples dancing on full Moon nights, all of which are immortalised by an array of Bollywood films. ​“Chander hanshi” is how Rabindranath Tagore describes the nurturing presence of the Moon smiling down upon us ³. 

An astonishing coincidence is that the Sun, which is four hundred times more distant from us than the Moon, has a diameter four hundred times greater than the Moon. This allows the Moon to perfectly obscure the Sun during a total solar eclipse. This is the kind of coincidence that makes even the staunchest atheist amongst us to question our beliefs. Our understanding of the universe has been immeasurably enhanced by eclipses. Einstein’s theory of General Relativity was experimentally verified in 1919 which fundamentally altered our view of how the universe works. Many unanswered questions about the outer layers of the solar surface and its corona continue to be investigated during solar eclipses making them one of the most anticipated natural phenomena. It is another remarkable fact that the Moon is receding from us by a few centimeters each year because of the energy lost from friction due to the tides. Total solar eclipses are a feature only of the present time – in a few million years they’ll cease to exist.

“That’s one small step for [a] man, one giant leap for mankind.” These were Neil Armstrong’s words upon setting foot on the Moon on 20 July 1969, the day we celebrate each year as International Moon Day. The first exploration of the Moon started just 10 years prior to this, and almost all missions in between were symbolic achievements inspired by the Cold War between the USA and the USSR. However, during this time several experiments and important tasks were conducted, such as placing retroreflectors on the Moon due to which we know its distance from us to an accuracy of a few millimetres. More recent explorations of the Moon have studied the composition of its soil (which is not very different from the Earth’s); the existence of water (yes, in the form of ice); its seismic activity (‘moonquakes’ do happen, one was detected by the Chandrayaan III lander, in fact); the range in surface temperature from day to night (a staggering 250°C), and so much more. 

Have you ever wondered what role the atmosphere plays in regulating the Earth’s temperature? A perfect way to answer this is to study the Moon which is at the same distance from the Sun as the Earth and does not have an atmosphere. This is precisely what Arrhenius and Langley did over a 100 years ago in a landmark piece of work ⁴. They went further and studied the effect of atmospheric CO₂ on the Earth’s temperature predicting global warming well before it was on anyone’s mind.

The age has now come when we are likely to impact the Moon as much as it has impacted us. The Moon is set to be used as a staging ground for further exploration of outer space. At one-sixth the mass of the Earth, the gravitational pull exerted by the Moon on any object is likewise lower and this means that it takes less energy to launch rockets from the Moon than from the Earth. A future human colony on the Moon will have its work cut out – lunar residents will have to assemble rockets from parts sent from the Earth, and launch them to the far reaches of the universe. However, there are many other reasons to live and work on the Moon. It is an excellent place for astronomy. Due to the lack of an atmosphere, the sky from the Moon appears dark even during the daytime. This means that an optical telescope can operate at all times, collecting exquisite pictures of stars, galaxies, and nebulae undistorted by any atmosphere. 

One of my graduate advisors mooted the idea of building a telescope on the ridge of a crater near one of the lunar poles. Such a telescope will almost always be illuminated by the Sun thereby allowing it to harness solar energy for its operation. The icy bottom of the crater, almost always in the dark, will provide enough water for the needs of the moon citizens ⁵. Loony, you may say, but a bold idea that has the potential to unlock many new discoveries. Such ground-based lunar telescopes can be much larger than what’s possible to launch into space, thereby enabling the observation of much fainter and distant objects. Radio astronomy on the Moon is another attractive proposition since there are few artificial radio signals on the Moon like there are on the Earth to interfere with cosmic sources ⁶.

The Moon is tidally locked to the Earth which means that the Moon rotates about its axis at the same rate as it revolves around the Earth. Thus, the length of the lunar day is 29 days, half of which is daytime and the other night. This is why we see only one face of the Moon from the Earth. We can communicate easily with spacecraft that land on this side of the Moon unlike on the ​“far side of the Moon”. On full moon nights, our imagination runs riot and we give the Moon unique names: Blue Moon (second full moon of the month), Harvest Moon (full moon nearest the autumnal equinox, when crops are harvested), Wolf Moon (full moon during the bitter winter), Blood Moon (a reddish-purple full moon during a lunar eclipse, when sunlight refracted by the Earth’s atmosphere falls on the Moon), and many more. 

The Moon was born from the Earth according to the Giant-Impact Hypothesis during the formation of the solar system about 4.5 billion years ago ⁷. Though it’s our child it also protects us, nurtures us, teaches us, and allows us to survive. It has a lot of responsibilities to bear and we are foisting much more upon it. Nearly every space-faring nation is planning to land spacecraft on the Moon over the next decade. We want to populate the Moon with humans and use it as a base for further colonisation of space. Some feel that The Moon could be our new home should climate change make the Earth uninhabitable. Will the Moon become our world? Or can we remain content gazing upon it through a telescope, exclaiming with wonder, ​“wow! It’s so beautiful!”?

About the author:

Proteep Mallik is faculty, Azim Premji University, Bengaluru campus. He worked for several years as an optical engineer, designing and building instrumentation for Biotechnology (DNA sequencing) and semiconductor (photomask inspection) companies. Apart from teaching undergraduate courses, Proteep works along with Azim Premji Foundation to conduct Science workshops for teachers, and to design experiments in science for school students.

Featured Photo credit: Proteep Mallik

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