VLBA Measures Asteroid's Characteristics
In an unusual observation, astronomers used the National Science Foundation's Very Long Baseline Array (VLBA) to study the effects on radio waves coming from a distant radio galaxy when an asteroid in our Solar System passed in front of the galaxy. The observation allowed them to measure the size of the asteroid, gain new information about its shape, and greatly improve the accuracy with which its orbital path can be calculated.
When the asteroid passed in front of the galaxy, radio waves coming from the galaxy were slightly bent around the asteroid's edge, in a process called diffraction. As these waves interacted with each other, they produced a circular pattern of stronger and weaker waves, similar to the patterns of bright and dark circles produced in terrestrial laboratory experiments with light waves.
"By analyzing the patterns of the diffracted radio waves during this event, we were able to learn much about the asteroid, including its size and precise position, and to get some valuable clues about its shape," said Jorma Harju, of the University of Helsinki in Finland.
The asteroid, named Palma, is in the main asteroid belt between Mars and Jupiter. Discovered in 1893 by French astronomer Auguste Charlois, Palma completes an orbit around the Sun every 5.59 years. On May 15, 2017, it obscured the radio waves from a galaxy called 0141+268 with the radio shadow tracing a path running roughly southwest to northeast, crossing the VLBA station at Brewster, Washington. The shadow sped across the Earth's surface at 32 miles per second.
(Score: 3, Informative) by PartTimeZombie on Sunday September 16 2018, @08:59PM (4 children)
Not quite 200 kilometres long.
Also, from the Wikipedia article:
which seems a bit unnecessary, how many main-belt asteroids are going to hit the Earth? It is something of a relief however. My lawn is just starting to look nice and it would make a mess.
(Score: 2) by takyon on Sunday September 16 2018, @11:01PM (1 child)
Pretty big for an asteroid. It's the 32nd largest known asteroid by diameter [wikipedia.org], out of hundreds of thousands known. I read the Wikipedia text you mentioned and yes it is silly.
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(Score: 2) by PartTimeZombie on Sunday September 16 2018, @11:04PM
Oh, yes, quite right. It is big for an asteroid, I think I was trying to make the point that it is small and hard to see from Earth.
(Score: 1, Interesting) by Anonymous Coward on Monday September 17 2018, @01:59AM (1 child)
I did a few calculations, based the stats on the Wikipedia page, for what would happen if it did hit the earth [ic.ac.uk]. The speed of 12.2 km/s is based on the asteroid's mean orbital velocity. The diameter of 191.524 is such that the volume times the listed 1.40 g/cm3 density yields the mass of 5.15×1018 kg. 3.83×1026 joules is about a thousand times more energy than that of the asteroid that killed the dinosaurs. The last time the earth might have experienced such an impact was at latest probably during the Late Heavy Bombardment, before the planet was fully formed.
(Score: 2) by PiMuNu on Monday September 17 2018, @11:16AM
So not good for lawns then?
(Score: 2) by MichaelDavidCrawford on Monday September 17 2018, @03:11AM
One can derive refraction from both the completely classical Maxwell's Equations or from the Quantum Uncertainty Principle.
In the case of Quantum it's easier to understand the diffraction around the edges of a pinhole. If you place a screen some distance behind the pinhole you won't see a sharp, round circle of light, rather it will be fuzzy on the edges. Either bright light - as with a laser - or the use of photographic film will reveal the alternating circles of light and dark.
Every photon has momentum in all three axes. If it's traveling straight along the X axis then one might say that its momentum in Y and Z is zero. That will be the case for a photon whose wavefunction is constant to Y and Z infinity.
But if you constrict that planar photon with a pinhole, you will measure its energy in the Y and Z directions: just expose that film for a measured amount of time, then use a digital scanner to measure how dark its spot is.
But by measuring its Y and Z contributions to energy, we simultaneously introduce uncertainty as to its Y and Z momenta. As we place the screen or film farther and farther behind the pinhole, that momentum will result in the spot with rings of bright and dark growing larger and larger in diameter.
This same phenomenon limits the resolution of small telescopes. That's why you need a big lens or mirror to resolve details on the planets, despite that they are very bright and so don't need a scope that can gather a lot of flux.
The resolution of large scopes is limited by atmospheric turbulence, however recent developments in adaptive optics have made that a much smaller problem with the result that the diffraction-limited resolution of large professional scopes being astoundingly fine.
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