Friday, August 12, 2016

Perseid Meteor Shower/Outburst

"The Perseids show up every year in August when Earth ventures through trails of debris left behind by the ancient Comet Swift-Tuttle as it makes its 133-year orbit around the sun. This year, Earth may be in for a closer encounter than usual with the comet trails that result in meteor shower, setting the stage for a spectacular display. An outburst is a meteor shower with more meteors than usual. The last Perseid outburst occurred in 2009."
Mashable:
Some forecasts are predicting that during its peak, meteor rates could be double the traditional rate expected for this shower that occurs each year around this time. This means there could be as many as 200 shooting stars per hour.

According to NASA meteor expert Bill Cooke, forecasts are showing that Jupiter's gravity has pulled some extra debris from the comet into Earth's path this year, meaning that the planet will pass through a thicker stream than usual.

"This year, the models show that Jupiter’s gravity has tugged streams of particles ejected from Comet Swift-Tuttle back in 1862, 1479, and 1079 closer to Earth’s path, which will lead to us seeing more Perseids than usual, perhaps double the normal rates," Cooke said.

If early morning on Friday won't work, however, you should still be able to see some Perseids shooting through the skies all week, it's just that the best rates should happen on August 12.

“Forecasters are predicting a Perseid outburst this year with double normal rates on the night of Aug. 11-12,” NASA meteor expert Bill Cooke said in a statement. “Under perfect conditions, rates could soar to 200 meteors per hour.”

It should be noted that "perfect conditions" are difficult to achieve for most people in the United States or in populous areas around the world.

The highest rates of meteors will only be visible to people in deep darkness, far from artificial light.


Stellar Scintillation
Stars twinkle because… they’re so far away from Earth that, even through large telescopes, they appear only as pinpoints. And it’s easy for Earth’s atmosphere to disturb the pinpoint light of a star. As a star’s light pierces our atmosphere, each single stream of starlight is refracted – caused to change direction, slightly – by the various temperature and density layers in Earth’s atmosphere. You might think of it as the light traveling a zig-zag path to our eyes, instead of the straight path the light would travel if Earth didn’t have an atmosphere.

Planets don’t twinkle because they are closer, and thus appear larger in our sky, as tiny disks instead of pinpoints.



The Autokinetic Effect
The autokinetic effect (also referred to as autokinesis) is a phenomenon of visual perception in which a stationary, small point of light in an otherwise dark or featureless environment appears to move. It was first recorded by a Russian officer keeping watch who observed illusory movement of a star near the horizon. It presumably occurs because motion perception is always relative to some reference point. In darkness or in a featureless environment there is no reference point, so the movement of the single point is undefined.

The direction of the movements does not appear to be correlated with the involuntary eye movements, but may be determined by errors between eye position and that specified by efference copy of the movement signals sent to the extraocular muscles. Several researchers, including Richard Gregory, have shown that autokinesis occurs when no eye movements are recorded. Gregory has suggested that with lack of peripheral information correcting movements that prevent eye movements due to muscle fatigue are wrongly interpreted as movement of the light.

Alexander von Humboldt observed the phenomenon in 1799 while looking at stars with the naked eye, but thought it was a real movement of the stars. Thus he named them "Sternschwanken" i.e. "Swinging Stars". It was not until 1857 that G. Schweitzer (Schweitzer, 1857), an early German psychologist, discovered that it was a subjective phenomenon. The US Navy started studying this in 1945 in order to explain vertigo experiences related by pilots. Today this "kinetic illusion" is categorized as a vestibular-induced illusion, see vestibular system.

Many sightings of UFOs have also been attributed to the autokinetic effect's action on looking at stars or planets.


More information:
» Space: "Meteor Showers and Shooting Stars: Formation, Facts and Discovery"

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