APOD: Geminid Meteors over Xinglong... (2015 Dec 23)

[APOD Robot]

Geminid Meteors over Xinglong Observatory

Explanation: Where do Geminid meteors come from? In terms of location on the sky, as the featured image composite beautifully demonstrates, the sand-sized bits of rock that create the streaks of the Geminid Meteor Shower appear to flow out from the constellation of Gemini. In terms of parent body, Solar System trajectories point to the asteroid 3200 Phaethon -- but this results in a bit of a mystery since that unusual object appears mostly dormant. Perhaps, 3200 Phaethon undergoes greater dust-liberating events than we know, but even if so, exactly what happens and why remains a riddle. Peaking last week, over 50 meteors including a bright fireball were captured streaking above Xinglong Observatory in China. Since the Geminids of December are one of the most predictable and active meteor showers, investigations into details of its origin are likely to continue.

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[aviojet]

Nice picture! The header shows the wrong date though.

[Ann]

Nice image! As a color commentator, I am of course very interested in the colors of the meteors. Since this is a composite image, the colors may not be absolutely comparable. I can't help noticing, however, that the brightest meteor is blue. Its true color may be more blue-green. What causes the color of the bright meteor and the different colors of the fainter meteors?

Ann

[Boomer12k]

Mass, speed, composition?

:---(===) *

[neufer]

[b][color=#0000FF]The larger spherical focusing mirror MB is at the top of the left-hand supporting column and the spectrographs are inside the right-hand column. (The almost-flat Schmidt corrector plate MA is in the left of the two domes at the right).[/color][/b]

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<<The 4m Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST), also known as the Guo Shoujing Telescope after the 13th-century Chinese astronomer, is a meridian reflecting Schmidt telescope, located in Xinglong Station, Hebei Province, China. The location, only 115 km (71 mi) NW of Beijing, is far from ideal, being in an area with high levels of both atmospheric and light pollution. Undertaken by the Chinese Academy of Science, the telescope is planned to conduct a 5-year spectroscopic survey of 10 million Milky Way stars, as well as millions of galaxies.

LAMOST is configured as a reflective Schmidt telescope with adaptive optics. There are two mirrors, each made up of a number of 1.1-metre (p-p) hexagonal deformable segments. The first mirror, is a Schmidt corrector plate in a dome at ground level. The almost-flat mirror MA reflects the light to the south, up a large slanted tunnel (25° above horizontal) to the larger spherical focusing mirror MB. This directs light to a focal plane 1.75 metres in diameter corresponding to a five-degree field of view. The focal plane is tiled with 4000 fibre-positioning units, each feeding an optical fibre which transfers light to one of sixteen 250-channel spectrographs below.

Using active optics technique to control its reflecting corrector makes it a unique astronomical instrument in combining large aperture with wide field of view. The available large focal plane may accommodate up to thousands of fibers, by which the collected light of distant and faint celestial objects down to 20.5 magnitude is fed into the spectrographs, promising a very high spectrum acquiring rate of ten-thousands of spectra per night.

The telescope is to conduct a wide-field survey, called the "LAMOST Experiment for Galactic Understanding and Evolution," or LEGUE. Particular scientific goals of the LAMOST include:

• An extra-galactic spectroscopic survey to shed light on the large scale structure of the universe
  
  A stellar spectroscopic survey, including a search for metal-poor stars in the galactic halo, to provide information on the structure of our Galaxy
  
  Cross-identification of multi-waveband surveys

It is also hoped that the vast volume of data produced will lead to additional serendipitous discoveries. Early commissioning observations have been able to confirm spectroscopically a new method of identifying quasars based on their infrared color.>>

[RJN]

Nice picture! The header shows the wrong date though.

Thanks! Fixed it. - RJN

[Chris Peterson]

Nice image! As a color commentator, I am of course very interested in the colors of the meteors. Since this is a composite image, the colors may not be absolutely comparable. I can't help noticing, however, that the brightest meteor is blue. Its true color may be more blue-green. What causes the color of the bright meteor and the different colors of the fainter meteors?

Color is complicated with meteors. Most of the color is produced by atmospheric gases, and in some cases meteoroid composition may affect color, too. In an image like this, the short trails near the radiant represent meteors that are traveling almost directly toward the camera. They are entering the atmosphere at a steep angle, and depending on their size may travel deeper and therefore encounter a wide range of atmospheric conditions. The meteors which are far from the radiant are shallower, and mostly higher. Their longer trails represent both a geometric effect, as well as probably longer duration (since they take a little longer to burn up at higher altitude).

The size of the meteoroid affects how hot it gets, as well as the physics of the heat production itself. The temperature impacts the spectrum, and therefore the color.

Add to all of this the various artifacts that can be created by the camera, such as what happens when your light source is made up of individual spectral lines but you collect the data through broad RGB filters, the effects of saturation in some color channels but not others, the variable exposure time created by a fast object moving across pixels (meteor exposure time is determined by meteor speed, not shutter time).

Really, given all the variables, it's remarkable that the colors are as consistent as they are!

[neufer]

[b][color=#0000FF]The natural colors of a meteor's emission lines. This spectrum of a Perseid was photographed by Julian Nott (U.C. Santa Barbara) using a digital camera equipped with a 1000 lines/mm objective grating during the Aurigid MAC test flight on August 13, 2007. Photo: NASA/Julian Nott (www.nott.com).[/color][/b]

---

American Meteor Society

<<The difficulties of specifying meteor color arise because meteor light is dominated by an emission, rather than a continuous, spectrum. The majority of light from a fireball radiates from a compact cloud of material immediately surrounding the meteoroid or closely trailing it. 95% of this cloud consists of atoms from the surrounding atmosphere; the balance consists of atoms of vaporized elements from the meteoroid itself. These excited particles will emit light at wavelengths characteristic for each element. The most common emission lines observed in the visual portion of the spectrum from ablated material in the fireball head originate from iron (Fe), magnesium (Mg), and sodium (Na). Manganese (Mn), Chromium (Cr), Copper (Cu) have been observed in fireball spectra, along with rarer elements. Silicon (Si) may be under-represented due to incomplete dissociation of SiO₂ molecules. The refractory elements Aluminum (Al), Calcium (Ca), and Titanium (Ti) tend to be incompletely vaporized and thus also under-represented in fireball spectra.

Vivid colors are more often reported by fireball observers because the brightness is great enough to fall well within the range of human color vision. These must be treated with some caution, however, because of well-known effects associated with the persistence of vision. Reported colors range across the spectrum, from red to bright blue, and (rarely) violet. The dominant composition of a meteoroid can play an important part in the observed colors of a fireball, with certain elements displaying signature colors when vaporized. For example, sodium produces a bright yellow color, nickel shows as green, and magnesium as blue-white. The velocity of the meteor also plays an important role, since a higher level of kinetic energy will intensify certain colors compared to others. Among fainter objects, it seems to be reported that slow meteors are red or orange, while fast meteors frequently have a blue color, but for fireballs the situation seems more complex than that, but perhaps only because of the curiosities of color vision as mentioned above.>>

[MarkBour]

Thanks, neufer, for posting the article about the LAMOST / Guo Shoujing Telescope and its mission. Sounds like some really massive datasets to be gathered. As an earth-based telescope, will its spectra be limited, or is it expected that lots of great data will be gathered here? Are Chinese astronomers likely to make their data available freely, even to the West? Will this result in a more detailed map of the stars in our galaxy, with relative motions? Are there other places that similar/competing data are being gathered that astronomers here are more interested in?

[Ann]

Thanks, Art, for that article about colors of meteors!

Ann

[BillBixby]

I, also, want to thank Art.

The 95% vs 5% cleared up discrepancies and misunderstanding I had regarding postings I had read.

[ta152h0]

Were these meteors all at once ? The background stars seem to be all points of light.

[Chris Peterson]

Were these meteors all at once ? The background stars seem to be all points of light.

No. It's a stack of (I think) 8-second exposures. The stars presumably appear fixed because they were the aligned in the stacking, and then the landscape was compostited into the final image.

[neufer]

the landscape was compostited into the final image.

Compost, v. t.: To mingle, as different fertilizing substances,
in a mass where they will decompose and form into a compost.

[Tekija]

Nice image! As a color commentator, I am of course very interested in the colors of the meteors. Since this is a composite image, the colors may not be absolutely comparable. I can't help noticing, however, that the brightest meteor is blue. Its true color may be more blue-green. What causes the color of the bright meteor and the different colors of the fainter meteors?

Color is complicated with meteors. Most of the color is produced by atmospheric gases, and in some cases meteoroid composition may affect color, too. In an image like this, the short trails near the radiant represent meteors that are traveling almost directly toward the camera. They are entering the atmosphere at a steep angle, and depending on their size may travel deeper and therefore encounter a wide range of atmospheric conditions. The meteors which are far from the radiant are shallower, and mostly higher. Their longer trails represent both a geometric effect, as well as probably longer duration (since they take a little longer to burn up at higher altitude).

The size of the meteoroid affects how hot it gets, as well as the physics of the heat production itself. The temperature impacts the spectrum, and therefore the color.

Add to all of this the various artifacts that can be created by the camera, such as what happens when your light source is made up of individual spectral lines but you collect the data through broad RGB filters, the effects of saturation in some color channels but not others, the variable exposure time created by a fast object moving across pixels (meteor exposure time is determined by meteor speed, not shutter time).

Really, given all the variables, it's remarkable that the colors are as consistent as they are!

And add also that there is no such physical thing as color, there are only objects that reflect or emit certain wavelengths of radiation and combnations thereof, and how these wavelengths stimulate our photoreceptors varies - about 10 percent of men and a much smaller fraction of women have one of them mutated which greatly alters spectral sensitivity, and many women carry a heteozygous mutation that theoretically can enhance color perception because they then have four rather than normal three types of light sensitive pigments in their retina - and how this information when relayed to the visual cortex is interpreted also varies considerably.

[Chris Peterson]

And add also that there is no such physical thing as color, there are only objects that reflect or emit certain wavelengths of radiation and combnations thereof, and how these wavelengths stimulate our photoreceptors varies - about 10 percent of men and a much smaller fraction of women have one of them mutated which greatly alters spectral sensitivity, and many women carry a heteozygous mutation that theoretically can enhance color perception because they then have four rather than normal three types of light sensitive pigments in their retina - and how this information when relayed to the visual cortex is interpreted also varies considerably.

And most of the information from the American Meteor Society about color isn't applicable to this image precisely because of that. What we see on camera images usually differs significantly from what we see with our eyes. I have thousands of witness reports which report completely different colors than what images show.

[Ann]

And add also that there is no such physical thing as color, there are only objects that reflect or emit certain wavelengths of radiation and combnations thereof, and how these wavelengths stimulate our photoreceptors varies - about 10 percent of men and a much smaller fraction of women have one of them mutated which greatly alters spectral sensitivity, and many women carry a heteozygous mutation that theoretically can enhance color perception because they then have four rather than normal three types of light sensitive pigments in their retina - and how this information when relayed to the visual cortex is interpreted also varies considerably.

And most of the information from the American Meteor Society about color isn't applicable to this image precisely because of that. What we see on camera images usually differs significantly from what we see with our eyes. I have thousands of witness reports which report completely different colors than what images show.

Still, Chris, very many different photographs show bright meteors as blue or green. I googled "bright meteors" and got many pictures of such meteors, where the majority appears to be predominantly blue or green.

Ann

[Chris Peterson]

And add also that there is no such physical thing as color, there are only objects that reflect or emit certain wavelengths of radiation and combnations thereof, and how these wavelengths stimulate our photoreceptors varies - about 10 percent of men and a much smaller fraction of women have one of them mutated which greatly alters spectral sensitivity, and many women carry a heteozygous mutation that theoretically can enhance color perception because they then have four rather than normal three types of light sensitive pigments in their retina - and how this information when relayed to the visual cortex is interpreted also varies considerably.

And most of the information from the American Meteor Society about color isn't applicable to this image precisely because of that. What we see on camera images usually differs significantly from what we see with our eyes. I have thousands of witness reports which report completely different colors than what images show.

Still, Chris, very many different photographs show bright meteors as blue or green. I googled "bright meteors" and got many pictures of such meteors, where the majority appears to be predominantly blue or green.

Oh yes, that's certainly true. But visual observers more commonly report much less saturated color, as well as a range of yellows, oranges, and reds that are not typically seen in photographs. Camera images are a poor representation of the visual experience of color.

[DavidLeodis]

It's an excellent scene. Though out of view on the left I suspect that there may have been just as much activity there. It would thus have been an even more wonderful sight.

On trying some online translations of the Chinese text with the image I was amused by one that translated 3200 Phaethon as 3200 Ernie.

[neufer]

Click to play embedded YouTube video.

Click to play embedded YouTube video.

<<The Fechner color effect is an illusion of color seen when looking at certain rapidly changing or moving black-and-white patterns. They are also called pattern induced flicker colors (PIFCs). Not everyone sees the same colors.

The effect is most commonly demonstrated with a device known as Benham's top. It can also be seen in stroboscopic lights when flashes are set at certain critical speeds. Rotating fan blades, particularly aluminum ones, can also demonstrate the effect; as the fan accelerates or decelerates, the colors appear, drift, change and disappear. The stable running speed of the fan does not (normally) produce colors, suggesting that it is not an interference effect with the frequency of the illumination flicker.

The effect was noted by Gustav Fechner and Hermann von Helmholtz and propagated to English-speakers through Charles Benham's invention of his toy top. The perceptual mechanism of Fechner color is not entirely understood. When the disk is spun, arcs of pale color are visible at different places on the disk. One possible reason people see colors may be that the color receptors in the human eye respond at different rates to red, green, and blue. Or, more specifically, that the latencies of the center and the surrounding mechanisms differ for the different types of color-specific ganglion cells. The phenomenon originates from neural activity in the retina and spatial interactions in the primary visual cortex, which processes pattern recognition (von Campenhausen & Schramme, 1995). Research indicates that the blue/yellow opponent process accounts for all the different PIFCs (Schramme, 1992).>>

[Chris Peterson]

Click to play embedded YouTube video.

Do you see colors here? I see nothing but grays. But I have a wheel like this that I use in the classroom, and with that I see lots of colors. So again, a difference I think in how our eyes perceive things directly and how cameras capture them (in this case with the added complexity of video, so time becomes a factor, not just the sensor dynamics).

[geckzilla]

I get what people are trying to say by "there is no such thing as color" but I beg to differ. Color is how our brains translate certain wavelengths of EM radiation into a signal we understand. Say you had a transcript in a foreign language and had it translated into your native language. It's like saying your native language doesn't exist because the message existed originally in that foreign language.

[Chris Peterson]

I get what people are trying to say by "there is no such thing as color" but I beg to differ. Color is how our brains translate certain wavelengths of EM radiation into a signal we understand. Say you had a transcript in a foreign language and had it translated into your native language. It's like saying your native language doesn't exist because the message existed originally in that foreign language.

The guy in the video is the only person I've ever heard claim that there's no such thing as color. And from the rest of his comments, it's clear that he's just saying that as a rhetorical device.

[neufer]

I get what people are trying to say by "there is no such thing as color" but I beg to differ. Color is how our brains translate certain wavelengths of EM radiation into a signal we understand.

The guy in the video is the only person I've ever heard claim that there's no such thing as color. And from the rest of his comments, it's clear that he's just saying that as a rhetorical device.

Yes, Ann, the not so terribly amazing Dr. B is wrong... there is color! Dr. B has been affected by the skepticism of a skeptical age. He does not believe what he sees. He thinks that nothing can be which is not comprehensible by his little mind. In this great universe of ours, man is a mere insect in his intellect as compared with the boundless world about him, as measured by the intelligence capable of grasping the whole of truth and knowledge. Alas! How dreary would be the world if there were no color! It would be as dreary as if there were no Anns. The eternal blue light with which childhood fills the world would be extinguished. Not believe in color! You might as well not believe in blue fairies!

[Chris Peterson]

Yes, Ann, the not so terribly amazing Dr. B is wrong...

What, no reference to Pleasantville? You're slipping, Art.

Click to play embedded YouTube video.