|
Tag: astronomy
Why Is the Night Sky Turning Red?
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.
Venus’s Day in the Sun: How the Transit Will Help Us Search for Other Earths
Mark Anderson has an M.S. in astrophysics, is a contributor to Discover, and has written about science and history for many other publications. His new book The Day the World Discovered the Sun: An Extraordinary Story of Scientific Adventure and the Race to Track the Transit of Venus has just been published by Da Capo.
Also see Paul Raeburns’s explanation of what investigating Venus can teach us about our own planet.
The 2004 Venus transit at sunrise
On Tuesday afternoon—for those in North, Central and parts of South America—the planet Venus will pass directly in front of the sun for seven hours. This rare spectacle, called the Venus transit, occurs twice within a decade, then not again for more than a century. But as fleeting as they are, transits of the past provided invaluable information about our place in the solar system—and, astronomers hope, this transit could help us glean more information on planets elsewhere in the galaxy.
In the 1760s, some of the age’s top explorers and scientists collaborated on dozens of expeditions across the planet to observe the Venus transit. These voyages launched the legendary careers of Captain Cook and the surveyors Mason and Dixon. The expeditions also represented the world’s first big science project—forefather to today’s Large Hadron Collider and Human Genome Project, in which an international community of hundreds or thousands collaborates on a single fundamental scientific problem at the frontier of human knowledge.
In the balance hung two of the greatest scientific and technological puzzles of the 18th century: discovering the Sun’s distance from the Earth and finding one’s longitude at sea. Read More
The Brilliant “Blunder” That Led to a Nobel Prize
In 1917, a year after his general theory of relativity was published, Einstein tried to extend his field equation of gravitation to the universe as a whole. The universe as known at the time was simply our galaxy—the neighboring Andromeda, visible to the naked eye from very dark locations, was thought to be a nebula within our own Milky Way home. Einstein’s equation told him that the universe was expanding, but astronomers assured him otherwise (even today, no expansion is evident within the 2-million-light-year range to Andromeda; in fact, that galaxy is moving toward us). So Einstein inserted into his equation a constant now known as “lambda,” for the Greek letter that denoted it. Lambda, also called “the cosmological constant,” supplied a kind of force to hold the universe from expanding and keep it stable within its range. Then in 1929, Hubble, Humason, and Slipher made their monumental discovery using the 100-inch Mount Wilson telescope in California of very distant galaxies and the fact that they were receding from us—implying that the universe was indeed expanding, just as Einstein’s original equation had indicated! When Einstein visited California some time later, Hubble showed him his findings and Einstein famously exclaimed “Then away with the cosmological constant!” and never mentioned it again, considering lambda his greatest “blunder”—it had, after all, prevented him from theoretically predicting the expansion of the universe.
Fast forward six decades to the 1990s. Saul Perlmutter, a young astrophysicist at the Lawrence Berkeley Laboratory in California had a brilliant idea. He knew that Hubble’s results were derived using the Doppler shift in light. Light from a galaxy that is receding from us is shifted to the red end of the visible spectrum, while a galaxy that is approaching us has its light shifted to the blue end of the spectrum, from our vantage point. The degree of the shift is measured by a quantity astronomers call Z, which is then used to determines a galaxy’s speed of recession away from us (when Z is positive and shift is to the red).
DISCOVER's Newsletter
Sign up to get the latest science news delivered weekly right to your inbox!
