APOD: Moonless Meteors and the Milky Way (2015 Aug 13)

[APOD Robot]

Moonless Meteors and the Milky Way

Explanation: Have you watched the Perseid meteor shower? Though the annual shower's predicted peak was last night, meteor activity should continue tonight (August 13/14), best enjoyed by just looking up in clear, dark skies after midnight. Of course, this year's Perseid shower has the advantage of being active near the August 14 New Moon. Since the nearly New Moon doesn't rise before the morning twilight many fainter meteors are easier to spot until then, with no interference from bright moonlight. The Perseid meteor shower last occurred near a New Moon in 2013. That's when the exposures used to construct this image were made, under dark, moonless skies from Hvar Island off the coast of Croatia. The widefield composite includes 67 meteors streaming from the heroic constellation Perseus, the shower's radiant, captured during 2013 August 8-14 against a background of faint zodiacal light and the Milky Way. The next moonless Perseid meteor shower will be in August 2018.

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[Dad is watching]

Cool Photo!!!

Would it be possible to capture the light from each meteor streak in a spectroscope in order to determine the chemical make-up of each individual meteor? Do they last long enough or produce enough of a light signature for that? And I wonder if they would vary (a little or a lot) if such analysis is possible.

[NGC3314]

Meteor spectroscopy is indeed done. It takes patience or a lot of automation, since the equipment has to be capable of grabbing the data at any time and very quickly. This means that a diffraction grating or prism is added to a wide-angle system, and take the occasional set of data when a meteor bright enough to register the spectrum comes through. The American Meteor society has an introduction. Much of the emission from meteor light is from our own atmosphere heated via compression as the meteoroid Jencounrefsthe atmosphere, with variations due to velocity and typical altitude of emission associated with the velocity, but, especially for bright fireballs, ratios of metallic elements from the meteoroid (aluminum, iron, magnesium...) have been derived.

(Cue Chris Peterson...)

[Asterhole]

If the meteor shower occurs during a "New Moon" phase, most of the light would come from reflected Earthshine, since we would be viewing the shadow side of the Moon. It seems dubious that this low-level light source would interfere with our seeing the meteor shower. Now, if it were the "Full Moon"...

[Steve Dutch]

Now if you could get that in a single frame, it would be worth getting up for. The hype over meteor showers makes me cringe. 100 an hour? Count slowly: "1,2,3....30 Whee! 1,2,3....Ooh!" Anything under 1000 an hour should be described as "weak."

What's the harm? Well, look at all the areas where the public has stopped listening to science. Then they get up at 2 AM, go outside, see a few meteors, but mostly nothing, and conclude that, once again, the scientists were wrong and don't know what they were talking about.

[henrystar]

Now if you could get that in a single frame, it would be worth getting up for. The hype over meteor showers makes me cringe. 100 an hour? Count slowly: "1,2,3....30 Whee! 1,2,3....Ooh!" Anything under 1000 an hour should be described as "weak."
What's the harm? Well, look at all the areas where the public has stopped listening to science. Then they get up at 2 AM, go outside, see a few meteors, but mostly nothing, and conclude that, once again, the scientists were wrong and don't know what they were talking about.

I absolutely agree. I was called at dinner yesterday to comment for a newspaper. I sipped my Martini, and I replied, no way, José!

[henrystar]

It is a great photo. It would be nice to know what the total exposure time was.

[Chris Peterson]

(Cue Chris Peterson...)

Actually, it is becoming quite routine to capture meteor spectra. With sensitive and inexpensive video systems, there are now a number of dedicated meteor spectroscopes being operated (many by amateurs) and thousands of meteor spectra captured. Quite a change in just the last few years.

One interesting thing to come from this is a substantial improvement in our ablation models. Different constituents of meteoroids vaporize at different temperatures, so we see the spectrum change over the luminous path as different elements burn. This also means that there's an altitude distribution of material, with things like sodium being dispersed at a higher altitude than refractory elements.

[Duffer]

What's the harm? Well, look at all the areas where the public has stopped listening to science. Then they get up at 2 AM, go outside, see a few meteors, but mostly nothing, and conclude that, once again, the scientists were wrong and don't know what they were talking about.

Seems to me that much of the complacency you mention is due to media hype. If it's not sensational it won't compete with other broadcasters so the data gets exaggerated to make it more interesting. Look at weather reporting for example.

[Chris Peterson]

Now if you could get that in a single frame, it would be worth getting up for. The hype over meteor showers makes me cringe. 100 an hour? Count slowly: "1,2,3....30 Whee! 1,2,3....Ooh!" Anything under 1000 an hour should be described as "weak."

So all regular showers are weak?

A hundred per hour is more than one per minute. I find that inexperienced observers (including children) are quite amazed by that level of activity, and will remain outside a long time watching if the weather is comfortable.

What's the harm? Well, look at all the areas where the public has stopped listening to science. Then they get up at 2 AM, go outside, see a few meteors, but mostly nothing, and conclude that, once again, the scientists were wrong and don't know what they were talking about.

I don't blame media "hype" for that, but rather, a change in culture towards instant gratification and short attention spans.

[Meekmoe]

Are the streaks from meteors near parallel in 3D space? Like the Solar Rays (Crepuscular Rays) that peak through clouds? If so, I assume only if they are with in a close time frame giving our viewing reference frame changes with the earths rotation..

[Chris Peterson]

Are the streaks from meteors near parallel in 3D space? Like the Solar Rays (Crepuscular Rays) that peak through clouds? If so, I assume only if they are with in a close time frame giving our viewing reference frame changes with the earths rotation..

Yes, the paths are parallel, but only at any particular time. The radiant of the shower is the vanishing point for the parallel tracks, and the radiant moves with the stars. However, the Perseid radiant has a pretty high declination (+58°), meaning it's not far from the pole and therefore moves across the sky slowly.

If you have a fixed camera an shoot the sky over several hours, the lack of a common origin will be detectable, if not grossly obvious. To get the best results, you can use a tracking camera, and then composite a single background on the final image. That will accurately maintain the relationship between the meteor trails and the sky.

[Chris Peterson]

85 Perseids captured last night from my camera in Colorado (despite thunderstorms until well after midnight).

[Coil_Smoke]

Are they truly meteors? OR...Is Lrrr attacking the Earth once again ???

[grump]

Maybe this is a dumb question, but why do meteor showers follow in the path of a comet? The physics of it eludes me.

I would have thought that material ejected from a comet would disperse generally in the direction it was ejected, and continue to orbit the sun in a new orbit. I can't work out why ejected material would follow roughly the same orbit as the comet many many years and centuries after the comet had passed by.

[geckzilla]

Are you doing any meteor spectroscopy yourself, Chris?

[Chris Peterson]

Maybe this is a dumb question, but why do meteor showers follow in the path of a comet? The physics of it eludes me.

I would have thought that material ejected from a comet would disperse generally in the direction it was ejected, and continue to orbit the sun in a new orbit. I can't work out why ejected material would follow roughly the same orbit as the comet many many years and centuries after the comet had passed by.

The material does disperse. Material ejected outward orbits more slowly, material ejected inward orbits more quickly. Furthermore, a small delta-v (we're talking about perihelion ejection velocities on the order of a few tens to a few hundreds of meters per second, from bodies with orbital speeds of tens of kilometers per second) means that the particle orbits, while different from the parent, won't be all that different. And depending on the direction of ejection, the major effect may be a slight change in eccentricity or inclination, not semi-major axis.

The effect of all this is to produce a slowly dispersing rather toroidal cloud of debris centered approximately on the path of the parent comet. Larger particles are closer to that path (they have lower ejection velocities). All of the material is swept out of orbit over time- most towards the Sun, but very small dust particles are swept outward. Meteor showers are sustained by the regular release of new material when the comet nears perihelion. Without that, the debris would be gone and the shower would evaporate.

[Chris Peterson]

Are you doing any meteor spectroscopy yourself, Chris?

I've fooled with it a little, but no serious monitoring. Might do more at some time in the future, as the costs have come down so much and the productivity has increased. I have friends and colleagues who have a serious investment in it, though.

[Ron-Astro Pharmacist]

This was an interesting site for specifics about the various meteor showers. I was surprised to see the Perseids are moving much faster than meteors from the other showers.

http://www.theskyscrapers.org/meteor-showers

Then I noticed it was in miles per hourfor the Perseids versus miles per second for the other showers. Still some interesting statistics.

I was trying to find information on a meteor shower that occured about 20 years ago. While watching this year's Perseids a friend was describing a shower that produced continuous meteors and many fireballs that broke into fragments. It was in the fall or winter probably early in the evening as he eventually gathered up the freezing kids and went inside. Any ideas on that specific event? I could find no reference.

[Chris Peterson]

I was trying to find information on a meteor shower that occured about 20 years ago. While watching this year's Perseids a friend was describing a shower that produced continuous meteors and many fireballs that broke into fragments. It was in the fall or winter probably early in the evening as he eventually gathered up the freezing kids and went inside. Any ideas on that specific event?

The Leonids (~ Nov 17) were extremely active from 1998-2002, producing meteor storms in 1999, 2001, and 2002. A bit under 20 years ago, but the most likely suspect.