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Take it to the limit

Sirius, brightest star in the sky, outshines Polaris, the north star – but only because Polaris is much farther away. If they were side by side in space, Polaris would be much the brighter. Distance makes stars look dim. By collecting more light than the unaided eye, telescopes make dim objects visible.

Even in the dark, the pupil of your eye – the “window” through which light enters – is only a fraction of an inch across.

The Hubble Space Telescope collects light with a mirror – a “pupil” – just shy of 8-feet across. Collecting vastly more light than the eye, Hubble can “see” objects on the far side of the universe.



Light travels through a vacuum at 186,000 miles a second – faster than anything else in the universe. But the universe is vast, and even light takes some time to reach our eye: from Sirius, eight years; from Polaris, 425 years. From the farthest galaxies whose light the Hubble has been able to capture, 12 billion years.

If you send a snapshot of yourself to a friend, she’ll see, not what you look like now, but what you looked like when you sent the picture.




We see Sirius as it was eight years ago; Hubble’s farthest galaxies, as they were 12 billion years ago. They, and the universe, were a lot younger then.

The telescope is a time machine, letting us see into the past.

The universe is less than 14 billion years old. Twelve billion years is a pretty impressive “lookback time.” And yet, given the size and quality of its mirror, the precision with which it can be aimed, and its location, above the atmospheric blur, the Hubble might be able to peer so far back that we could see into an era in which the universe was very different from the way it is today.

To look so far away, at objects so dim, the telescope needs to stare outward, at a single point in space, minute after minute, hour after hour, day after day, collecting one photon – one particle of light – after another, until it has collected enough to paint an image that we can study, and image we can examine for structure, pattern, color.

To keep its gaze steady, three gyroscopes stabilize Hubble in much the way that its spinning wheels keep a bicycle stable (imagine trying to balance a bike when the wheels aren’t spinning). The spinning rotors of the gyros connect to the outside world via wires of copper-silver alloy. The super-fine wires are wearing out. Hubble will likely have only two good gyros by the end of next year.

Hubble’s nickel-hydrogen batteries are slowly losing their ability to take a charge from the solar panels. In three years or so, their capacity will drop below what the scope needs to do useful science.

With new gyros and fresh batteries, and with the installation of new instruments (now wrapped in plastic and lying in storage) Hubble – and we – could find ourselves looking back into an era never-before seen in visible light – an era when the universe was dark – and the first stars were turning on.

We’ve yet to see what the Hubble can do to the limit of its abilities.

While scientists and engineers debate whether Hubble should be rescued by a manned shuttle mission or an by an unmanned robot, government support for the rescue is evaporating. As the nation’s space budget is now proposed, the Hubble Space Telescope will be allowed to die, and then dropped into the ocean.


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