Tag: light

Why Is the Night Sky Turning Red?

By Guest Blogger | August 23, 2012 12:59 pm

Amy Shira Teitel is a freelance space writer whose work appears regularly on Discovery News Space and Motherboard among many others. She blogs, mainly about the history of spaceflight, at Vintage Space, and tweets at @astVintageSpace

The idea of a red sky at night used to invoke beautiful images of vibrant sunsets, the product of warm sunlight bathing the sky near the horizon. The adage of “red sky at night, sailor’s delight” refers to a calm night ahead; a red sunset suggests a high-pressure system in the west is bringing calm weather. But red skies at night have taken on a new meaning in recent decades. As outdoor lighting become increasingly prominent, our night skies are gradually turning from black to red.

This discovery came from a team of scientists led by Christopher Kyba from the Freie Universitaet and the Leibniz Institute of Freshwater Ecology and Inland Fisheries. The scientists were tracking the effects of cloud cover on light pollution when the realized the colour of the night is changing. Their report, entitled “Red is the New Black,” was just published in the journal Monthly Notices of the Royal Astronomical Society.

Until relatively recently, nights skies were quite dark. The only major source of light was the Moon, allowing us to see thousands of individual stars and the wide, glowing swath of the Milky Way across the sky. Then people started illuminating the outdoors and nights became brighter. Benjamin Franklin helped promote street lamps in the U.S. and improved the designs of these early versions, which were made from candles in glass cases on top of high posts. These were replaced by gas lamps starting in Baltimore in 1816, which remained popular until Thomas Edison introduced the light bulb. Electric streetlights first appeared in Cleveland in 1879 and were the dominant form of street illumination by the turn of the century. As electricity became more affordable, the number of street lamps increased, turning dark city skies into a thing of the past.

This useful light doesn’t confine itself to the paths and streets we want to illuminate—much of it gets scattered by and into the atmosphere. This sky glow is a common phenomenon seen over busy urban areas. Some types of light fixtures produce more of a glow than others. Street lamps open on the top, unfocused lights, and upward-facing lights, like those placed under billboards, drastically increase the amount of sky glow. The more light sent upwards, the more light scattered back down by the atmosphere.

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CATEGORIZED UNDER: Top Posts

Rest Easy, Einstein—Faster-Than-Light Neutrinos Would Not Violate Relativity

By Amir Aczel | October 3, 2011 9:45 pm

By now you’ve probably heard the widely reported news about the possible discovery of neutrinos that allegedly travel faster than light. The OPERA (Oscillation Project with Emulsion tRacking Apparatus) collaboration of almost 200 scientists working at the Gran Sasso underground laboratory in central Italy has discovered a phenomenon the physicists could simply not explain. For over three years, the scientists have been collecting data on the flight of neutrinos—those mysterious, nearly massless particles that can travel through anything at immense speed—originating in the SPS accelerator at CERN, near Geneva, and traveling underground all the way to Gran Sasso, 731 kilometers (about 450 miles) away. The experiment showed that the 16,000 neutrinos measured at Gran Sasso had traveled there through Earth’s crust at faster than light speed.

Facing a crowded lecture hall at CERN last Friday, Dario Autiero of the OPERA group explained how the researchers went to great lengths to remove any sources of error in their measurements: they measured distances using an extremely high-precision GPS called PolarX, measured time at the two locations to an accuracy of one nanosecond using cesium clocks, and accounted for the tides, Earth’s rotation, variations between day and night and spring and fall, etc. The statistical significance of the finding was six-sigma—meaning that the probability that the experimental result was a random fluke was only one in a billion. For a full hour after the presentation, Dr. Autiero was grilled by a roomful of physicists, and seemed to be able to account for all of the many potential errors brought up by the audience.

But physicists remain very skeptical. They want to see a confirmation of the findings from another experiment in a separate laboratory before they accept such a bizarre finding. After all, this result, if true, would appear to run against the spirit of Einstein’s special theory of relativity. When I showed the Gran Sasso paper to Nobel Laureate Steven Weinberg, he told me: “It looks pretty impressive, but I still think that this will go away.” The sentiment was echoed by almost every physicist I have spoken with since. The results seem mind-boggling. After all, nothing can go faster than light, right?

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CATEGORIZED UNDER: Space & Physics, Top Posts
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