Roemer knew that the true orbital period of Io could have nothing to do with the relative positions of the Earth and Jupiter. In a brilliant insight, he realized that the time difference must be due to the finite speed of light. That is, light from the Jupiter system has to travel farther to reach the Earth when the two planets are on opposite sides of the Sun than when they are closer together. Romer estimated that light required twenty-two minutes to cross the diameter of the Earth’s orbit. The speed of light could then be found by dividing the diameter of the Earth’s orbit by the time difference.
The Dutch scientist Christiaan Huygens, who first did the arithmetic, found a value for the speed of light equivalent to 131,000 miles per second. The correct value is 186,000 miles per second. The difference was due to errors in Roemer’s estimate for the maximum time delay (the correct value is 16.7, not 22 minutes), and also to an imprecise knowledge of the Earth’s orbital diameter. More important than the exact answer, however, was the fact that Roemer’s data provided the first quantitative estimate for the speed of light, and it was in the right ballpark.
What’s interesting was that at the time the true distance from the Earth to the Sun was unknown, making this measurement either incredibly lucky or incredibly insightful.
Excerpt from Cosmic Horizons from the American Museum of Natural History.
If the weather clears up at all this week, there’s a good chance of catching some meteors during the Geminid meteor shower:
This week is a great chance to watch a great meteor shower: the Geminids, so named because they appear to shoot away from the constellation of Gemini. This is a really reliable shower, generally putting out as many as 100 meteors per hour! It peaks on the evening to morning of Dec. 13/14, but usually has a decent showing for a couple of days before and after the peak.
First things first: In November, I posted a how-to guide on watching a meteor shower for the Leonids, another nice annual shower. The instructions for the Geminids are essentially the same. Just replace “Leo” with “Gemini” in your head when you read the guide, and you’ll be fine. Gemini rises in the east around 7:00 p.m. local time, but the best time to observe is after local midnight (see #3 in the how-to guide).
Just remember: if you’re anywhere close to a major city, you’ll have a much better time if you drive somewhere darker. This dark sky map is a good way of finding suitable viewing areas near you: Dark Sky Finder.
via Bad Astronomy.
A brief history of the gas discharge tube, and the first public demonstration of the neon discharge tube 102 years ago today.
Claude’s associate, Jacques Fonseque, sold the first neon-advertising sign to a Paris barber in 1912. The next year saw a breakthrough, as boulevardiers gazed upon 3.5-foot neon letters spelling “CINZANO.”
Claude had applied for a U.S. patent Nov. 9, 1911, and Patent 1,125,476 was awarded Jan. 9, 1915. Claude then sold licenses to the new invention in other countries.
via This Day In Tech | Wired.com.
Prior to his historic dive to the bottom of the Mariana Trench, James Cameron explored the 8.2 km deep New Britain Trench, a region never before explored by human or robot:
In terms of biology, the New Britain Trench looked like New York City compared to the desert at the bottom of the Mariana Trench. On dives with the submersible and with robotic vehicles, the team found thriving communities of acorn worms and sea anemones at the bottom of the New Britain trench, which were fed by nutrients coming from nearby islands. “There was a lot of nutrient input,” says Douglas Bartlett, a microbiologist at the Scripps Institution of Oceanography in La Jolla, California. “It was incredible to see logs at 8.2 kilometres.”
via Nature, The Scuttlefish.