Starship Asterisk*

Delphinid Meteor Mystery

Explanation: Over a five hour period last Tuesday morning, exposures captured this tantalizing view of meteor streaks and the Milky Way in dark skies above Las Campanas Observatory in Chile. During that time, astronomers had hoped to see an outburst from the gamma Delphinid meteor shower as Earth swept through the dust trail left by an unknown comet. Named for the shower's radiant point in the constellation Delphinus, a brief but strong outburst was reported in bright, moonlit skies on June 10, 1930. While no strong Delphinid meteor activity was reported since, an outburst was tentatively predicted to occur again in 2013. But even though Tuesday's skies were dark, the overall rate of meteors in this field is low, and only the three lower meteor streaks seem to point back to the shower's estimated radiant.

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I found it absolutely amazing that, from an unexpected and largely unverified meteor spotting back in 1930, a prediction for a possible re-sighting could be made for June 10, 2013 ..... How could enough information be captured back then to be able to make this prediction?

biddie67 wrote:I found it absolutely amazing that, from an unexpected and largely unverified meteor spotting back in 1930, a prediction for a possible re-sighting could be made for June 10, 2013 ..... How could enough information be captured back then to be able to make this prediction?

It wasn't. The shower is a known one. I record several GDEs every year. I had four this year, including a bright fireball that was also observed by several cameras in New Mexico, allowing the radiant to be narrowed down.

The shower is caused by a long period comet (unidentified) and by modeling the one-revolution dust trail it was predicted an outburst could occur in 2013. Apparently it didn't, but the data the calculation was based on was not of as good quality as that we have when making shower predictions for short period cometary parents.

I am sure it is not just a finely determined thing that ALL meteors are going to point back exactly to the point of origin....general direction is probably more likely...and that is not to say that some individual meteors coming from "slightly off" are not going to get through. After all debris is hitting us all the time....


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Boomer12k wrote:I am sure it is not just a finely determined thing that ALL meteors are going to point back exactly to the point of origin....general direction is probably more likely...and that is not to say that some individual meteors coming from "slightly off" are not going to get through. After all debris is hitting us all the time....

No, at any one time the radiant is very small- usually less than a degree in diameter. Stuff can't come from different directions, because it's all in pretty much the same orbit. The radiant is simply determined by the velocity of the Earth and the velocity of the meteoroid stream at the time of impact- and all the meteoroids have the same velocity. There are some more minor effects that can affect radiant position, as well, but they act on all the particles about the same. These can result in somewhat larger radiants, up to several degrees in diameter. But as a rule, we can think of the physical radiant as being a point.

The radiant does move with time, drifting in a predictable and measurable way. But this is slow, not typically observed over a single night.

I was about to ask how long comet material would stay out in Earth's orbital path and was in the middle of typing it when I suddenly remembered reading about this minute effect the sun has on a nearby dust grain. I'm feeling sheepish because when I read about it I wondered why anyone bothered to study orbiting dust grains.

geckzilla wrote:I was about to ask how long comet material would stay out in Earth's orbital path and was in the middle of typing it when I suddenly remembered reading about this minute effect the sun has on a nearby dust grain. I'm feeling sheepish because when I read about it I wondered why anyone bothered to study orbiting dust grains.

Modeling streams is complex. You need to consider P-R, radiation pressure (which acts in the other direction), and the perturbations of Jupiter, Saturn and sometimes other planets as well.

Is the photo a composite?
No star trails, no blured horizon...

Ultimately all of those things mean there's not going to be any leftover streams from comet impacts millions of years ago, which would have been nifty reminders had they stayed long enough.

tetrodehead wrote:Is the photo a composite?
No star trails, no blured horizon...

You figured it out.

geckzilla wrote:Ultimately all of those things mean there's not going to be any leftover streams from comet impacts millions of years ago, which would have been nifty reminders had they stayed long enough.

Yup, the Solar System is very good at keeping itself clean. Outside the planets, the asteroid belt, and the distant ice objects, nothing is stable enough to last very long. Very small dust is blown away by radiation pressure. Larger dust falls into the Sun because of the P-R effect (the dust responsible for the zodiacal light is being continuously replenished from comets). Comets only have lifetimes of dozens or hundreds of orbits, before they are perturbed into the Sun, Jupiter, or out of the Solar System. Likewise for asteroids that get knocked out of the Belt. Anything knocked off a planet isn't going to be in orbit for more than a few million years.