The Universe responds to #10YearChallenge

The cosmos ages on such a vast timescale that it would take a very keen astronomical eye and a very powerful camera to detect changes in its face in our lifetime.

January 28, 2019 06:22 pm | Updated January 29, 2019 04:47 pm IST

As Carl Sagan said, we are a way for the cosmos to know itself. But if we are to know the cosmos, gazing at it is the way to go.

As Carl Sagan said, we are a way for the cosmos to know itself. But if we are to know the cosmos, gazing at it is the way to go.

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Your social media feeds were probably filled with the viral #10YearChallenge these last two weeks. What started off as a way to show how one has aged over a decade spawned accusations of ageism, narcissism, and even of sinister designs to train face-recognition algorithms. People have since used this to highlight the effect of climate change, bad governance and so on.

Ten years is an ideal period of time to measure changes in a human being, but our lifetimes are but ‘a blip on the timeline of eternity’. So, how would the Universe itself respond to #10YearChallenge?

For millennia, we knew that the stars did not change their positions from one night to the next. Except, that is, five bright ones which could clearly be seen moving over days, or even weeks. We know them as our nearest planets, of course. Apart from these planets, the unchanging sky was something humankind took for granted, and was reassured by. Which is why comets, which seemed to come and go as they please, caused panic in many civilisations. Comets aside, the sudden appearance of a ‘guest star’ in 1604 C.E. which then faded away over months, posed a serious challenge in Europe to the Aristotelian view of the unchanging cosmos. This was the famous Kepler’s Supernova.

Not only is every planet, star and galaxy perpetually moving; it is constantly evolving as well. However, their sizes and separations are beyond our comprehension or even imagination. Hence, we can see them change only if we are are very close to them, or if they move incredibly fast.


But first, how fast can we see the Universe change, sitting on Earth? The entire sky seems to rotate around us once a day, and the Sun seems to rotate around us once a year. We can see the Moon move against the background stars over hours, and the planets, over a few days. The axis of the Earth precesses (gradually rotates such that the angle of its axis changes) roughly every 25,770 years, and thus the pole star and the coordinates of all the stars do change over thousands of years. Our solar system, and all the stars that we can see, are moving around the Galactic centre, and this will cause the shape of the constellations to change visibly over tens of thousands of years. Stars much more massive than our Sun evolve over only millions of years, ending their lives in a supernova explosion that last a matter of minutes. However, our Sun and less massive stars evolve slowly over billions of years. In the meantime, our neighbouring Andromeda Galaxy is hurtling towards the Milky Way and will collide with us in 4 billion years. The Moon itself is slowly moving away from us and sadly, 100s of millions of years hence, it will be too small in the sky to cause any more total solar eclipses for us, provided we are still around then, to enjoy. Indeed, the sky seems to change on every timescale we can imagine.

What about the Universe as a whole? Carl Sagan popularised the idea of a ‘cosmic calendar’. If the entire age of the Universe — 13.8 billion years — were to be scaled down to one year, starting with the Big Bang on January 1, then the first galaxies formed around January 22, but the Milky Way formed only on March 16. Our solar system formed as late as September 2 and the first life on Earth arose around 19 days later. Animals migrated onto land around December 22, and modern humans arose on December 31 at 11.52 p.m. All of modern history has occurred only in the last second!

Exploding stars eject their outer layers at 1000s of km/s and we can actually see this expansion from objects in our own Galaxy or very nearby. Here are some images that the Public Outreach and Education Committee (POEC) of the Astronomical Society of India (ASI) came up with as its contribution to #10YearChallenge. The images of the supernova 1987A in visible light and radio clearly show how this object has changed over 20 years.


Does this mean that we can see such changes within a human lifetime only if they are near enough? Not necessarily. Cosmic timescales are huge, but if our telescopes could produce images with sufficient detail (or resolution), then we could even detect changes in objects much farther away, provided they moved that much faster for their distance from us.

The timelapse images below, depicting a radio jet from a black hole in galaxy 3C 111, is one such example. This is a jet of plasma ejected by a supermassive black hole at a speed very very close to the speed of light itself. 3C 111 is about 700 million light years away from us. We can see how this jet has changed over only 10 years by using a radio telescope that is equivalent to one that is as big as the United States of America!


It is not just incredibly fast or very close-by celestial objects that change over a few years. Our knowledge of the cosmos itself changes by extraordinary amounts over such a period (probably because a typical PhD thesis takes that long too). The final ‘10-year challenge’ comparison below shows how much our knowledge has grown in a field that was purely the realm of science fiction as recently as a couple of decades ago — namely, exoplanets. Mainly because of telescopes like the Kepler Mission, we have now, in 2019, discovered 10 times the number of planets around other stars compared to what we knew in 2009. Who knows what the next ten years will teach us about our Universe?



Our cosmos is a never-ending source of surprises. It is full of events that happen ever so slowly, but somewhere, sometime, an entire star can explode in just minutes. It is full of objects that span unimaginable sizes, but if we look at nearby ones with sufficiently powerful telescopes, we can glimpse such large structures changing before our very eyes. Hopefully, humanity will be able to tackle something that is certainly changing rapidly, in the coming 10 years — the climate — so that we can continue to gaze at the Universe in amazement. Meanwhile, as a friend pointed out to me, our astronomy-themed ‘10 year challenge’ pictures can at least serve to confuse those face-recognition algorithms that expect to see a nose on all pictures hash-tagged as #10YearChallenge!

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