Astronomy Picture of the Day 9-06-02

NASA ^ | 9-06-02 | Robert Nemiroff and Jerry Bonnell

[petuniasevan]

Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2002 September 6

HESS Gamma-Ray Telescope
Credit: The HESS Collaboration

Explanation: Most ground-based telescopes with lenses and mirrors are hindered by the Earth's nurturing, protective atmosphere that blurs images and scatters and absorbs light. But this telescope was designed to detect extreme gamma rays - photons with over 100 billion times the energy of visible light - and actually requires the atmosphere to operate. As the gamma rays impact the upper atmosphere they produce air showers of high-energy particles. Adorned with 382 separate mirrors each 60 centimeters in diameter and equipped with a fast camera, the telescope records in detail the brief flashes of optical light, called Cherenkov light, created by the air shower particles. The telescope pictured here was inaugurated this week and is intended to operate as part of the High Energy Stereoscopic System (HESS) array under construction in Namibia. The initial phase of HESS will consist of four telescopes working in concert to provide multiple stereoscopic views of the air showers, relating them to the energies and directions of the incoming cosmic gamma rays.

[petuniasevan]

Astronomy Fun Fact:

Cherenkov radiation can be said to be the light equivalent of a sonic boom. In a medium such as air or water, the speed of light is considerably less than the speed of light in vacuum (c). An energetic particle enters the atmosphere at c. It's now moving faster than light does in air. A cascade of photons ensues - that's the light shower that the HESS telescope detects. It is important to remember that the cosmic rays are not travelling faster than c. They are just travelling faster than light does after it has been slowed down by passing through a material. Also: The blue glow in the water surrounding nuclear reactors is Cherenkov radiation. For more information visit THIS SITE or HERE.

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[petuniasevan]

[MeekOneGOP]

[BossyRoofer]

Can't wait to see the images from this process! GO APOD!

[RightWhale]

It's now moving faster than light

People say, yes, of course, but this phenomenon ought to cause relativity theory brain synapses to twist up into klein bottles. It's a big problem.

[Notforprophet]

Why did they build it in Namibia?

[petuniasevan]

HESS is a German project. Namibia used to be called German South West Africa in the early 20th century. German settlers moved there by the thousands. South Africa seized power there in 1915 and incorporated it. The area was home to guerrilla warfare - remember SWAPO? - for decades until independence was achieved in 1990.

I'm supposing that the HESS project is a money source for the Namibian government, and perhaps a German attempt at a bribe to ease persecution of the white minority population.

Namibia isn't exactly a human-rights showcase.

[sleavelessinseattle]

Wow...I don't think I'd want a job as lens polisher on that unit if the "War Veterans" don't want me to be!