A measure of the universe, in that pulsar. About tiny angles, vast distances and unimaginable speeds. (Which means the explosion actually happened 22,000 years ago, since G292.0+1.8 is 20,000 light years from us.) That is, this was an explosion so monumental, so cataclysmic, that the star-the star!-it expelled into space is, 2000 years later, still hurtling along at two million kmph. Scientists calculate that had we humans been able to observe the explosion of G292.0+1.8, that would have been 2,000 years ago. Compare with the car that trundled past at 18kmph. That is a speed of.wait for it.over two million kmph. It took ten years to cover those 190 billion km. Gargantuan or not, we can now calculate how fast the pulsar is moving. It’s well over a thousand times the distance between the sun and our planet.
Some fairly easy calculation tells us: about 190 billion km. Exactly like we can use 11 degrees and 100m to work out the 20m length of that stretch of road, we can use 0.00006 degrees and 20,000 light years to work out how far the pulsar travelled in 10 years. Though “minuscule" is hardly the word for this pulsar’s actual movement. Yet Chandra had detected a movement that minuscule. You certainly have no way to measure such an angle. An inadvertent twitch of your finger would be far larger. How far had it moved? Well, if you did the same finger pointing exercise spelled out above, your finger would have traced out an angle of.wait for it.0.00006 degrees. Comparing both, astronomers found that a particular dot of light had, just like the car above, moved. Chandra produced an image of G292.0+1.8 in 2006, and then again in 2016. It is designed specifically to observe, among other objects, exploded stars. So we have telescopes such as Nasa’s Chandra X-Ray Observatory, which was launched into orbit around the earth in 1999. If you could see it in the sky-which you can’t-you might stare at it for hours, weeks and years on end, and you would not detect it moving. But the stars are so distant that without instruments, we’ll never notice their movement. Yet we know they are constantly moving, because we have instruments that can detect or deduce movement in different ways. As far as humans can see with our naked eyes, none of them has moved for millennia. Think of any star at all-the ones in the beloved constellation Orion, known in India as Shikari or Kalpurush, for example. Not so easy with objects out in the cosmos.
Though there’s a more basic question: How do we even know the pulsar is moving? In the case of the car, you actually see it move. The point of this digression is to put in your mind the question that astronomers naturally ask about the pulsar that G292.0+1.8 kicked out: how fast is it moving? In this case, the angle would be just over 11 degrees. Given that and the 100m distance to the road, some elementary trigonometry lets you calculate the length of the visible stretch of road. Measure the angle through which the finger swivels.
Point a finger at the right end, then swivel it till it points at the left end. One more thing about this thought experiment: if you didn’t know, how might you calculate that the stretch is 20m long? Here’s one way. How fast was the car travelling? That’s easy: Four seconds for 20m, that’s 5m/s, which translates to 18kmph. Exactly four seconds later, the car disappears to the left. As you watch, a car appears at the right end of the stretch of road and you hit the button on your stopwatch. Give the scene some numbers: the road is 100m from you, and the stretch is 20m long. Let’s say you’re standing at your window and looking at a short stretch of the nearby road, stopwatch conveniently at hand.
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