Politics, Policy & the Chance of Change: The Conversation Yearbook 2015 by John Watson

Author:John Watson [Watson, John]
Language: eng
Format: epub
Tags: Social Science, Political Science, World, Australian & Oceanian, Sociology, General
ISBN: 9780522869828
Google: fMkACwAAQBAJ
Publisher: Melbourne Univ. Publishing
Published: 2015-11-23T12:39:43+00:00

The only Remedy is a most serene and quiet Air, such as may perhaps be found on the tops of the highest Mountains above the grosser Clouds.

While astronomers do place telescopes atop of high mountains, the ultimate solution is a telescope in space. In space, the clarity of Hubble’s images (defined by angular resolution) is limited by the size of its 2.4-metre mirror rather than atmospheric turbulence. From this vantage point, in visible light Hubble can see details roughly 25 times smaller than most Earth-bound telescopes can.

Being in space gives Hubble incredible advantages compared to Earth-bound telescopes. But Hubble isn’t meaningfully closer to the stars than us. It’s just 540 kilometres above the Earth, which is nothing compared to astronomical distances. Indeed, it’s so close you can sometimes spot Hubble speeding by.

In the 1990s, a team of astronomers, led by Wendy Freedman, Rob Kennicutt and Jeremy Mould, exploited the clarity of Hubble’s images to find the bright variable stars in galaxies millions of light years from Earth. With these stars, astronomers measured the distances to these galaxies, which enabled the first precision measurement of the expansion rate of the Universe.

The detail of Hubble’s images has been crucial to its ongoing success. It has enabled astronomers to view changing weather and aurora on other planets, measure the gravitational deflection of light by dark matter, peer into stellar nurseries and glimpse planets orbiting other stars.

Innovations

For the past two decades astronomers have been discovering planets orbiting distant stars. Some of these planets transit, passing between their stars and us, so they block a tiny percentage of the starlight that we would otherwise see. Transits that cause stars to dim by 1% are regularly detected by ground-based telescopes.

A far greater challenge is detecting the almost imperceptible additional dimming during a transit caused by light being blocked by particular elements and molecules in a planet’s atmosphere. This requires measuring a 0.01% change in brightness: a perfect job for Hubble in the vacuum of space.

In 2000, David Charbonneau, Tim Brown and their colleagues used Hubble to detect sodium in the atmosphere of a planet orbiting the star HD 209458. This is incredibly innovative science, which was not imagined by Hubble’s designers four decades ago, when the only known planets were in our own solar system. Astronomers finding new ways to exploit Hubble’s unique advantages is a key reason for Hubble’s continuing success.

Light and dark

When we look at the night sky, we are seeing only a small portion of the spectrum of light. Ultraviolet and infrared light is invisible to our eyes. Even if we could see ultraviolet light, it is largely blocked by the ozone layer.

Furthermore, when we look up at the stars, we don’t just see the starlight. We can see dark trees silhouetted against the night sky. The air literally glows, and it is particularly bright in infrared light.

From its vantage point in space, Hubble can see a broad spectrum of light against an exceptionally dark sky. This allows it to see further than Earth-bound telescopes.

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