Venus, though the twin of our planet, stands in complete contrast to it in almost every aspect, if not in all aspects. It is the brightest planet. it is the second planet from the Sun. One factor that completely sets this planet apart from ours is that it rotates “clockwise.” Therefore, the east witnesses the sun setting instead of rising and vice versa.

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On Earth, our view of the illuminated part of the Moon changes each night, depending on where the Moon is in its orbit, or path, around Earth. When we have a full view of the completely illuminated side of the Moon, that phase is known as a full moon.

But following the night of each full moon, as the Moon orbits around Earth, we start to see less of the Moon lit by the Sun. Eventually, the Moon reaches a point in its orbit when we don’t see any of the Moon illuminated. At that point, the far side of the Moon is facing the Sun. This phase is called a new moon. During the new moon, the side facing Earth is dark.

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Astronomy is one of the oldest natural sciences. The early civilizations in recorded history made methodical observations of the night sky. These include the Babylonians, Greeks, Indians, Egyptians, Chinese, Maya, and many ancient indigenous peoples of the Americas. In the past, astronomy included disciplines as diverse as astrometry, celestial navigation, observational astronomy, and the making of calendars. Nowadays, professional astronomy is often said to be the same as astrophysics.

Objects of interest include planets, moons, stars, nebulae, galaxies, and comets. Relevant phenomena include supernova explosions, gamma ray bursts, quasars, blazars, pulsars, and cosmic microwave background radiation. More generally, astronomy studies everything that originates beyond Earth’s atmosphere. Cosmology is a branch of astronomy that studies the universe as a whole.

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https://youtu.be/U3PV8xydvsU

Can you name the four most massive moons of jupiter? No.. Not a problem we got you!

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So, come let’s dig into this Game of Galaxies. Fasten your seat belts & brace for the impact!

THE JOURNEY

Andromeda is our closest neighboring galaxy, 2.5 million light years away from us. If I was to write this distance in kilometres, it would have 20 digits, so yes, it’s a huge distance!

Fueled by gravity, the galaxies are moving towards each other at a speed of 110 Km/s or 402,000 Km/h. To put this speed into perspective, moving at 110 km/s, you could go around the Earth in just 6 minutes. 

(Source : https://www.nasa.gov/mission_pages/hubble/science/milky-way-collide.html)

After 4 Billion years, the first contact between the two galaxies would happen, the galactic collision would begin, and would continue to take place over the span of another 2 Billion years.

THE SHOW BEGINS

As the galaxies would close in, one would see Andromeda getting bigger and bigger in the night sky. However, the magnificent spiral in the sky would be just the beginning, soon a show of cosmic choreography would begin, a dance of stars & planets on the rhythm of gravity would follow in one of the most ecstatic galactic collisions the human race might ever come to experience.

Below is an illustration by NASA on what a person on Earth would witness in the sky, during the course of 6 Billion years. Each picture differs by roughly 0.7 Billion years, which means the first picture is the night sky, today, and the last one is the night sky, 6 Billion years later.

(Source : https://www.nasa.gov/mission_pages/hubble/science/milky-way-collide.html)

During the course of 4 Billion years, Andromeda would keep getting closer and closer to us, until we have touchdown. Now the collision finally begins, we’re in the endgame.

ENDGAME

So, what happens next?

Well, simply put, now the two galaxies would “collide”. However, a galactic collision differs greatly from a collision of two solid objects, like footballs because of what galaxies are made up of and how they work. A galaxy is a gravitationally bound system of stars, dust, gas & planets. They generally also have a Black Hole at their center, which holds the complete system together. 

Enough with the theory, now let us visualize the collision. 

So, arrange two pieces of transparent paper, and make a disk outline on both of these. Fill this disk with tiny dots using your pen, make a lot of dots. Do the same for both the papers. Now, overlap the two papers. You would notice some dots overlap, while some do not. 

The disk is the galaxy, the dots are the stars. The overlapping dots are the stars that would collide into each other, while the non-overlapping ones are the ones who would survive without a scratch. 

This is a simulation by NASA where you can see how the showdown would happen.

(Click the image to open the link)

So, now the two galaxies & their central black holes would merge over the course of another 2 billion years to form a new central black hole & a new system of stars & planets around it. The two galaxies would combine to form a new galaxy!

But what happens to the stars and planets, wouldn’t all of them collide and get destroyed?

Yes, some would. But surprisingly enough, most stars & even our solar system might survive the collision, the reason is that stars have a lot of empty space between them, so it gets really difficult for two stars to land at just the right spot to collide. Most stars would pass right beside each other. 

THE AFTERMATH

The darkest of nights lead to the brightest of mornings.

After 6 Billion years, as the dust settles, things would start to calm down. The stellar cosmic choreography would come to an end and the two galaxies would become one, the “Milkdromeda”.

The galaxy would contain a much bigger, Super Super Massive Black Hole at its center and our solar system would probably be thrown out somewhere on the outskirts of the galaxy.

But where would we be?

It’s incredible how much our humankind has advanced into technology & space exploration. As time passes by, newer technologies arrive, discoveries are made, and we make one more step into deep space, far away from our Earth and Solar System.

But we would soon be put to a test. Much before the galaxy comes racing our way, our own Sun would end up consuming us. In 1 billion years, it would be so luminous it would evaporate all the water on Earth! LIfe on Earth as you know it, wouldn’t be possible and it’s evident that we need to leave!

Our survival is on the line, the humans to come would be the ones who’d have to make us an intergalactic race, they’d have to migrate to another stellar system, go out into the unknown, so that a kid like me, or a kid like you, would then be able to look up in the sky, and see what we would miss.

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So, let’s dive in & see what our moon is up to!

MOONLIGHT OR SUNLIGHT?

Firstly, you can let go of the idea of the moon changing shape, The moon is a celestial, spherical body, of fixed dimensions, which is in constant motion around the Earth and the reason it “appears” to change shape is actually the fact that the moon does not produce light of its own, it merely reflects our sun’s light back to Earth. 

So, when you look up at the moon, and you notice how it lights up the night sky with it’s “moonlight”, that light is actually the sun’s light, hitting the moon’s surface and getting reflected towards you. The moon is kind of like a mirror in the night sky, trying to sneak in some of the sun’s light onto you, while you are on the dark side, away from the bright sun. 

MIRROR MIRROR IN THE SKY

So now that we know that the moon is essentially just kind of like a “mirror” reflecting the sun’s light on us, we can see how it “appears” to change its shape. The phases of the moon are just a simple consequence of how much of the surface of the moon is illuminated by the sun on a particular night.

The three musketeers, the sun, the moon & the earth, are in constant motion relative to each other at all times. The sun sits at the center of the solar system, the Earth goes around the sun, while the moon goes round the Earth!

(Source: https://media.proprofs.com/images/QM/user_images/2503852/New%20Project%20(78)(28).jpg)

As the moon moves between the Earth & the sun, the amount of area that:

• receives sunlight 
• And is also visible to us from the Earth 

varies continuously and it is this variation that leads to the phases of the moon..

PHASES OF THE MOON

So, now that we know how the moon moves relative to the Earth & the sun, and how it reflects the sun’s light, let’s see how our beautiful moon goes from a shining bright circle to complete darkness every month.

The moon completes one cycle around the Earth every 28 days. This means it goes from full moon to new moon & back to full moon, in 28 days.

When the moon is right in between the sun & earth, we cannot see it’s bright side, since it is facing away from us, towards the sun, so that is your “New Moon”, complete darkness as no light can be reflected from the moon, to you.

When it completes half an orbit from “New Moon” position, it is now away from both the sun & the Earth, Now imagine you are standing on the dark side of the Earth, the sunlight would fall on the moon & be reflected back to you, you would see the complete circle, the “Full Moon”.

When half the side of the moon facing earth is lit up, these phases are called first and third quarters.

When the visible lighted surface seems to be getting bigger, we say the moon is waxing, & when it seems to be getting smaller, we say the moon is waning. Also, when more than half of the visible moon is lit, we call it gibbous & when less than half of it is lit up, we call it crescent.

(Source: https://www.natgeokids.com/wp-content/uploads/2018/05/Phases-of-the-Moon-Orbit.jpg)

So, that was all about how the moon “appears” to change shape. Remember, it doesn’t, it’s just a matter of how much of its surface is lit by sunlight and how much of that lit surface you can see at a time. 

TRY AT YOUR  HOME

Here is an interesting experiment from the wonderful team at NASA, which you can do at home to understand how all this works.

1. Use a pencil & a styrofoam ball for the setup, fix the ball on the pencil.
2. Go into a dark room & set up a source of light, a bulb, or a lamp.
3. Stand in front of the lamp, holding the pencil upright in your hand.

The light source is now the Sun, the ball is the Moon, and you are the Earth.

Now rotate while standing in your place, you would see how the ball would enact the phases of the moon.

(Source: https://www.jpl.nasa.gov/edu/teach/activity/moon-phases/)

Have Fun!