August 5 The very idea of a space telescope is far-out, no pun intended. It makes a whole lot of sense, of course - because it won't have to deal with dust and ambient light and pollution that earthbound telescopes are tormented by. But that we would design, build and rocket such an instrument into space? Audacious and inspiring.
We did it 30 years ago, with the Hubble Space Telescope. Last December, the James Webb Space Telescope lifted off, and it's now stationed a cool million miles away. Far out indeed. And from that vantage point, it has started looking out at our universe and has already sent us some beautiful, breathtaking images. My Mint column today addresses that - but not the beauty so much as how far these objects are and what that means. Meet the oldest object ever seen, https://www.livemint.com/opinion/columns/meet-the-oldest-object-ever-seen-11659639047752.html Your thoughts welcome. cheers, dilip --- Meet the oldest object ever seen One of the great scientific endeavours of our times has just started delivering. Maybe you've noticed? I refer to the James Webb Space Telescope (JWST), that was fired into space last December. Settled into its position about a million miles away, it took its time to unfurl mirrors and get its equipment functioning. Then ... ... by now, no doubt you've seen the spectacular first few images from the JWST. There's the Southern Ring Nebula, like some glowing beetle. There's the Carina Nebula, what looks like a bank of roiling orange clouds with stars gleaming above in a deep royal blue field. There's Stephan's Quintet, five galaxies like ethereal nymphs doing an elaborate dance; that one photograph is actually a mosaic of about 1000 separate images. And this week, there's a dramatic view of Jupiter like you've never seen Jupiter, in gleaming black-and-white like some ancient warrior's shield. Just beautiful, each photograph. And yet they are not what's really remarkable about the JWST's performance. What is remarkable, is how far into the cosmos it has been able to peer. Let me give you a flavour of that, and the implications. Take the Southern Ring Nebula. It is about 2000 light-years (ly) from us on Earth. How far is that, really? What does that distance actually mean? Start by remembering that a "light-year" is a measure of distance, not time. It is the distance that light travels in a year. Now light moves along at about 300,000 km every second. That's so fast as to seem pretty much instantaneous, which is why you see the lamp on your wall turn on as soon as you press the switch. But of course it is not really "as soon as", not actually instantaneous. Think about this by imagining that when you press the switch, the fixture on the wall gently lobs a tennis ball at you. The ball takes a moment - maybe a second - to reach you. In the same way, the light from the lamp takes a slice of time - a tiny fraction of a second - to reach you. Over much larger distances than the few metres between you and your lamp, the time light takes to travel becomes perceptible, rather than apparently instantaneous. For example, light needs about eight minutes to get from the Sun to the Earth. That's a distance of about 150 million km, but we could also say that the Sun is eight light-minutes from us. Jupiter, for its part, is 36 light-minutes away. One light-minute, the distance light travels in a minute, is 300,000 km x 60 = 18 million km. We can do a similar calculation for a light-year: 1 ly = 300,000 km x 60 x 60 x 24 x 365 = 9,460,800,000,000 km. Call it 9.5 trillion km. The Southern Nebula is 2000 ly, or 19,000,000,000,000,000 (19 quadrillion) km away. All those zeros tell you why, for astronomical distances, the light-year is an easier unit to work with than the kilometer. Still, whichever unit you use, the Southern Nebula is almost unimaginably far off. Yet the truth of our awe-inspiring universe is that, stacked up against other objects out there, the distance to the Southern Nebula is almost unimaginably minuscule. The Carina Nebula is 7600 ly distant, or over twice as far as the Southern. If you're not impressed by "over twice", Stephan's Quintet is ... wait for it ... 290 million ly away. That's 150,000 times as far as the Southern Nebula. Take your time to grasp that. I find it hard, because even that vast distance is small change compared to some still farther objects the JWST has shown us. In mid-July, a team led by Harvard astronomer Rohan Naidu announced that they had spotted a galaxy, GLASS-z13, whose light took about 13.4 billion ly to reach JWST. That's nearly 50 times as far as Stephan's Quintet. That's also the most distant galaxy humans have ever observed. Now grasp this: GLASS-z13 is also the oldest galaxy humans have ever observed. How do we know this? Remember the Sun is eight light-minutes away. So when we look at it in the sky, we see it where it was eight minutes ago. When it "rises", it's actually eight minutes further along on the path it will trace in the sky through the day. Extend that reasoning to the Southern Nebula. Because light from there has taken 2000 years to reach us, we are actually seeing it as it was 2000 years ago. In a very real sense, when you look out at objects in the sky, you are looking back in time. You are looking at an eight minute-old Sun, at a 2000 year-old Southern Nebula, at a 7600 year-old Carina Nebula. It's a good bet the Sun hasn't exploded or vanished in those eight minutes, but what about those Nebulae? For all we know, they may not even exist today. And these are all relatively nearby objects. The five galaxies in Stephan's Quintet are 290 million years old. GLASS-z13 is 13.4 billion years old. Compare that last number to the age of our universe itself. Since it was born in the vast cataclysm we call the Big Bang, it's been about 13.8 billion years. So the very old GLASS-z13 actually offers us a glimpse of what a very young universe - aged a mere 400 million years - was like. And all this is also why astronomers typically refer to objects such as GLASS-z13 by age - "the oldest galaxy ever observed" - rather than distance. Given that everything in the universe is also moving, GLASS-z13 is today certainly not where it was 13.4 billion years ago. In fact, astronomers estimate it is now actually about 33 billion ly from us. How do they know that? The "z13" is a clue. That story, in another column. For now, let's just savour JWST's early findings, savour the wonder and excitement in them. -- My book with Joy Ma: "The Deoliwallahs" Twitter: @DeathEndsFun Death Ends Fun: http://dcubed.blogspot.com -- You received this message because you are subscribed to the Google Groups "Dilip's essays" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/dilips-essays/CAEiMe8q8wuqn66yJw43P6uTMqCGXAyu%3D9YrZ9vKDEiLwBWnqyg%40mail.gmail.com.
