Monday, May 04, 2015

202.6 - And Another Thing: the Hubble Space Telescope at 25

The Hubble Space Telescope at 25

I don't know how I missed this last week but I did. This past Friday, April 24, was the 25th anniversary of the launch of the Hubble Space Telescope.

The Hubble Space Telescope was named for Edwin Hubble, the American astronomer who in the 1920s showed first that the Milky Way is not the only galaxy, expanding our sense of the scale of the universe by a factor of multiple billions, and then later in the decade proved that the universe is not static but is expanding. The Hubble was conceived from the beginning as a telescope in space, one designed to operate outside the atmosphere of Earth and so without the visually-distorting effects of looking through that atmosphere.

It has worked brilliantly at that. But it didn't start that way. About a month after the telescope was set in orbit during a space shuttle mission came what's called in the trade "first light," the first image to be seen through a new telescope. It came - and it was blurry.

The media reaction was harsh. It was a failure, a boondoggle, a waste, a washout, useless. None of that was really true: Even the blurry images were superior to what could be obtained by Earth-bound observatories. But they were not nearly what they should have been or what the Hubble was designed to produce. It was a huge disappointment.

The problem was quickly diagnosed as spherical aberration, where light striking close to the edges of the telescope's primary mirror is not focused at the same place as light striking the mirror closer to the center, resulting in a blurred, out-of-focus image. The primary mirror in the Hubble is 2.4 meters (just about 8 feet) across and it was, in the words of one, "perfectly flawed" - it was made to the exact specifications called for, but the specifications were a little off. And so, therefore, were the images the mirror produced.

Happily for the Hubble, some optics specialists figured out a way to add small mirrors to correct for the aberraion, a process some described as fitting the telescope with a pair of glasses. In 1993, three years after the launch, another space shuttle mission did repairs - and the results were fantastic.

When those first images began to hit the media, for maybe the first time, no one needed to have an excuse for being an astronomer. No one needed to answer the inevitable "So what's the point?" for their interest in the stars and the galaxies and what they are made of and how they form and what will happen to them.

In the words of Adam Frank, an astrophysics professor at the University of Rochester, Hubble
showed us the universe in ways we simply could not have imagined before. When it showed us light-year-spanning cathedrals of gas where new stars are born, Hubble revealed a new kind of grace. When it showed us glittering but ancient jewels marking the apocalyptic death of stars, it spoke of power on a scale words cannot embrace. Hubble gave humanity a new visual vocabulary for space.

But it was not just a matter of the glorious look of the images. It was what they revealed.

The Hubble Space Telescope triggered the discovery of the still-not-understood dark energy when it showed us that not only is the universe expanding, the rate at which it's expanding is increasing. The effect has been likened to throwing a ball into the air and having it rise faster and faster as it goes up.

The Hubble gave us our first visible-light picture of an exoplanet, a planet orbiting a star other than our Sun.

It has advanced the search for extraterrestrial life with its ability to reveal something about the atmospheres of exoplanets, where it has found cases of carbon dioxide, organic molecules, and even water vapor in some of those atmospheres.

It has advanced our understanding of black holes, those collapsed remnants of massive stars were local gravity is so great that even light can't escape and has provided evidence that a supermassive black hole lies at the heart of almost all galaxies (including our own Milky Way), advancing our knowledge of how galaxies form.

It enabled us to watch the impact of a comet or asteroid on Jupiter almost in real time.

It has enabled us to look deep into the history of the cosmos. Remember that the speed of light is not infinite; light takes time to get from one place to another. What you see is not how an object is at your own "now" but how that object was at time moment the light left it. Which means the further out into space you go, the further back in time you are looking. By looking into deep space, Hubble has enabled us to look into deep time to see galaxies and clusters as they were billions of years ago.

And by looking at those exoplanets, the Hubble Space Telescope has even helped better our understanding of how our own Earth formed.

Quoting Adam Frank again:
From planets to black holes to the large-scale structure of the universe entire, you'd be hard-pressed to find a domain of cosmic science whose textbooks haven't been rewritten because of the Hubble Space Telescope.
The fact is, how we see space and our place in the cosmos we now see through Hubble's eyes; it is a reflection of what the Hubble Space Telescope has seen and shown us.

The Hubble is nearing end of its life. The original plan was for periodic maintenance missions but with the end of the shuttle program in 2009, that possibility is gone. NASA expects that in another year or two the telescope's instruments will start to break down. At some point, it will be brought down from orbit, most of it to burn up in the atmosphere and the rest to splash down in the Pacific Ocean.

That won't be the end of the story, however, just the Hubble's chapter. The next space telescope, the James Webb Space Telescope, is to launch in 2018. It's an infrarad-detecting scope. Why is that important? Because of the expansion of space, the further away something is, the faster it is moving away from us. As it does so, the wavelength of the light it emits gets stretched, making the light redder and redder. It's called redshift and astronomers can use it to tell how far away an object is. (It's also how Edwin Hubble proved the universe is expanding.) It's a visual version of the Doppler effect, usually illustrated by noting how the sound a ambulance siren makes changes as it approaches you, goes by, and moves away.

The point of all this is that if an object is far enough away, the light it emits becomes so redshifted that it is no longer in the visual spectrum but is in the infrared. Yes, the Hubble could take images in the infrared, but the James Webb telescope is designed to maximize abilities in that range. Which means that by "seeing" in the infrared, the James Webb Space Telescope may well be able to see further out in space - and so further back in time - than even the Hubble could.

We'll have to wait to see what new wonders that can reveal.

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