Re: [meteorite-list] Very Bright Fireball Over Europe on Halloween Night
Hi Doug- I don't think atmospheric extinction normally plays much of a role in color perception of bright meteors. You don't get a full magnitude difference between red and blue until you are about 15° above the horizon, or about four air masses. And even at a magnitude difference, I'd only expect a small impact on perceived color. Angle, however, translates to apparent speed, and I do think that might be an important factor in how people perceive color. I will say, however, that I haven't found any sort of systematic shift in color reports based on the distance from the fireball to the witness. Chris *** Chris L Peterson Cloudbait Observatory http://www.cloudbait.com On 11/4/2015 8:25 PM, Doug Ross wrote: Thanks for the very informative and interesting discussion. Could the altitude, angle and distance from which a meteor is viewed also affect perceived color? Seems to me that the air between the fireball and the witness might significantly filter the colors, in the same way that the sun can appear red at sunset, viewed at a low angle through more atmosphere. Doug Ross __ Visit our Facebook page https://www.facebook.com/meteoritecentral and the Archives at http://www.meteorite-list-archives.com Meteorite-list mailing list Meteorite-list@meteoritecentral.com https://pairlist3.pair.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] Very Bright Fireball Over Europe on Halloween Night
Op 5-11-2015 om 2:48 schreef "Beatty, Kelly" : this discussion is timely. what you've noted is exactly my understanding. just yesterday I came across a high-profile blog about these fireballs, Phil Plait's? and the writer stated that most of the light comes from the superheated vaporized particle as it ablates. suspecting this was wrong, I looked in several places for the correct information -- IMO, AMS, RASC Handbook, etc -- and yet I didn't really find the physics spelled out explicitly. (maybe I was looking in the wrong places?) the closest I came was this post by Peter Jenniskens (http://leonid.arc.nasa.gov/meteor.html), which was equivocal. Information on this indeed is not very consolidated but spread far and wide in primary literature, some dating to the '30-ies to '60-ies when Millman did a lot of groundbreaking spectroscopic work on meteors. More recent work on meteor spectra has been done by a.o. Borovicka. Chris Peterson rightly points to the influence of human physiology on colour perception: as he mentions, especially under low light level conditions the human eye is not as perceptive for each colour. Take also into account that on average 1 in 4 males have a form of colour blindness. Age plays a role as well: deep sky observers know that young people see planetary nebula as blue, while older people see them more greenish: this is due to the yellowing of the cornea with age. In other words: coupling meteor colours to meteor composition indeed is not as straight forward as some pretend. - Marco - Dr Marco (asteroid 183294) Langbroek Dutch Meteor Society (DMS) e-mail: d...@marcolangbroek.nl http://www.dmsweb.org http://www.marcolangbroek.nl - __ Visit our Facebook page https://www.facebook.com/meteoritecentral and the Archives at http://www.meteorite-list-archives.com Meteorite-list mailing list Meteorite-list@meteoritecentral.com https://pairlist3.pair.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] Very Bright Fireball Over Europe on Halloween Night
Yes Doug, I agree with you. In fact, I witnessed the very scenario you described. It was a long duration (earth-grazing) fireball that I was lucky enough to catch early-on in its flight. While it was at high elevation the fireball was a bright-blue ball with a greenish coma. As it streaked down to the horizon, it changed to a greenish-yellow flame, and as it approached the horizon it became a much dimmer, reddish sparkler. The flight-path gave me the distinct impression that the fireball was travelling away from me, much more than it was travelling downward. This helped me rationalize that the fireball hadn't really "dimmed" in brightness at the horizon. I was sure that it was just as bright and bluish-green for any lucky observers down-range and who were directly beneath the fireball, at the same point in its flight-path where I perceived it as being "reddish". Just as you worded it, Doug, the color changed "the same way that the sun can appear red at sunset, viewed at a low angle through more atmosphere." So, were in agreement then, that color AND magnitude are in the eye [and view angle] of the beholder. Bob V. On Wed, 11/4/15, Doug Ross via Meteorite-list To: "Meteorite List" Cc: "Matson, Rob D." Date: Wednesday, November 4, 2015, 7:25 PM Thanks for the very informative and interesting discussion. Could the altitude, angle and distance from which a meteor is viewed also affect perceived color? Seems to me that the air between the fireball and the witness might significantly filter the colors, in the same way that the sun can appear red at sunset, viewed at a low angle through more atmosphere. Doug Ross > HI All, > > Marco took the words out of my mouth. Getting tired of hearing that a green > meteor tells you anything about its composition. I know that it's natural > for people to think the most important thing they can report about a meteor > is its color, but I wish various broadcast media would do the public a > service and disabuse them of this notion. It would be far better if witnesses > could be trained to get in the habit of counting the duration accurately, > and noting the exact time of the meteor to the nearest minute. Seeing as > how almost everyone has a cell phone these days, and all cell phones have > accurate clocks, there really is no excuse to get the time wrong. Yet even > a casual browse of the AMS fireball site reveals that people clearly don't > think getting the time right is important. And even more obvious is that > most people have no business reporting anything about fireball starting > and ending bearings and elevation angles. --Rob > > -Original Message- > From: Meteorite-list [mailto:meteorite-list-boun...@meteoritecentral.com] > On Behalf Of Marco Langbroek via Meteorite-list > Sent: Wednesday, November 04, 2015 12:06 AM > To: meteorite-list@meteoritecentral.com; baa...@zagami.jpl.nasa.gov > Subject: Re: [meteorite-list] Very Bright Fireball Over Europe on Halloween > Night > >> A lot of folks say it looked green to them, which means it may have been >> metallic; > > > It is a perpetuated misunderstanding that meteor colours are primarily due > to > their composition. It's a science myth inspired by High School Bunsen burner > experiments that appears hard to kill. > > While composition in some cases does have some influence on the colour, it > is > actually the composition of the atmosphere that is usually dominant for our > perception of meteor colours. > > That certainly is true for green colours. Meteor spectra show that meteors > usually are very strong at the "forbidden" Oxygen line at 5577 Angstrom > (557.7 nm). > This line is due to atmospheric Oxygen, the same atmospheric Oxygen > exitation line also responsible for the green colours of Aurora. > > So green meteor colours are likely atmospheric in origin and say little > about the meteoroids' composition. > > - Marco > > - > Dr Marco (asteroid 183294) Langbroek > Dutch Meteor Society (DMS) > > e-mail: d...@marcolangbroek.nl > http://www.marcolangbroek.nl __ __ Visit our Facebook page https://www.facebook.com/meteoritecentral and the Archives at http://www.meteorite-list-archives.com Meteorite-list mailing list Meteorite-list@meteoritecentral.com https://pairlist3.pair.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] Very Bright Fireball Over Europe on Halloween Night
Thanks for the very informative and interesting discussion. Could the altitude, angle and distance from which a meteor is viewed also affect perceived color? Seems to me that the air between the fireball and the witness might significantly filter the colors, in the same way that the sun can appear red at sunset, viewed at a low angle through more atmosphere. Doug Ross > HI All, > > Marco took the words out of my mouth. Getting tired of hearing that a green > meteor tells you anything about its composition. I know that it's natural > for > people to think the most important thing they can report about a meteor > is its color, but I wish various broadcast media would do the public a > service > and disabuse them of this notion. It would be far better if witnesses > could be trained to get in the habit of counting the duration accurately, > and noting the exact time of the meteor to the nearest minute. Seeing as > how almost everyone has a cell phone these days, and all cell phones have > accurate clocks, there really is no excuse to get the time wrong. Yet even > a casual browse of the AMS fireball site reveals that people clearly don't > think getting the time right is important. And even more obvious is that > most people have no business reporting anything about fireball starting > and ending bearings and elevation angles. --Rob > > -Original Message- > From: Meteorite-list [mailto:meteorite-list-boun...@meteoritecentral.com] On > Behalf Of Marco Langbroek via Meteorite-list > Sent: Wednesday, November 04, 2015 12:06 AM > To: meteorite-list@meteoritecentral.com; baa...@zagami.jpl.nasa.gov > Subject: Re: [meteorite-list] Very Bright Fireball Over Europe on Halloween > Night > >> A lot of folks say it looked green to them, which means it may have been >> metallic; > > > It is a perpetuated misunderstanding that meteor colours are primarily due > to > their composition. It's a science myth inspired by High School Bunsen burner > > experiments that appears hard to kill. > > While composition in some cases does have some influence on the colour, it > is > actually the composition of the atmosphere that is usually dominant for our > perception of meteor colours. > > That certainly is true for green colours. Meteor spectra show that meteors > usually are very strong at the "forbidden" Oxygen line at 5577 Angstrom > (557.7 > nm). This line is due to atmospheric Oxygen, the same atmospheric Oxygen > exitation line also responsible for the green colours of Aurora. > > So green meteor colours are likely atmospheric in origin and say little > about > the meteoroids' composition. > > - Marco > > - > Dr Marco (asteroid 183294) Langbroek > Dutch Meteor Society (DMS) > > e-mail: d...@marcolangbroek.nl > http://www.marcolangbroek.nl __ Visit our Facebook page https://www.facebook.com/meteoritecentral and the Archives at http://www.meteorite-list-archives.com Meteorite-list mailing list Meteorite-list@meteoritecentral.com https://pairlist3.pair.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] Very Bright Fireball Over Europe on Halloween Night
Meteor color is important. It's just not a very useful measure for determining composition. Color changes with meteor speed and meteor depth in the atmosphere. And certainly, the composition is a factor, both in terms of chemical composition and bulk properties. But the relationship is complex, so there's no simple correlation between these things and color that we can make much use of. Common groups of factors tend to lead to common colors, which is why we see specific colors with specific showers. Chris *** Chris L Peterson Cloudbait Observatory http://www.cloudbait.com On 11/4/2015 3:16 PM, kashuba via Meteorite-list wrote: Rob, Marco, OK, so color isn't important. But why the different colors? Not green can't mean no oxygen. Is the green overwhelmed by other colors? Why? - John John Kashuba Bend, Oregon __ Visit our Facebook page https://www.facebook.com/meteoritecentral and the Archives at http://www.meteorite-list-archives.com Meteorite-list mailing list Meteorite-list@meteoritecentral.com https://pairlist3.pair.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] Very Bright Fireball Over Europe on Halloween Night
Different colors because there are different constituents in our atmosphere. Unless people are recording meteors with a spectrograph reporting "color" is useless since everyone sees colors differently, and the human eye is hardly a scientific calibrated device. Michael in so. Cal. On Wed, Nov 4, 2015 at 2:16 PM, kashuba via Meteorite-list wrote: > Rob, Marco, > > OK, so color isn't important. But why the different colors? Not green > can't mean no oxygen. Is the green overwhelmed by other colors? Why? > > - John > > John Kashuba > Bend, Oregon > > -Original Message- > From: Meteorite-list [mailto:meteorite-list-boun...@meteoritecentral.com] On > Behalf Of Rob Matson via Meteorite-list > Sent: Wednesday, November 04, 2015 12:54 AM > To: 'meteorite-list' > Subject: Re: [meteorite-list] Very Bright Fireball Over Europe on Halloween > Night > > HI All, > > Marco took the words out of my mouth. Getting tired of hearing that a green > meteor tells you anything about its composition. I know that it's natural > for > people to think the most important thing they can report about a meteor > is its color, but I wish various broadcast media would do the public a > service > and disabuse them of this notion. It would be far better if witnesses > could be trained to get in the habit of counting the duration accurately, > and noting the exact time of the meteor to the nearest minute. Seeing as > how almost everyone has a cell phone these days, and all cell phones have > accurate clocks, there really is no excuse to get the time wrong. Yet even > a casual browse of the AMS fireball site reveals that people clearly don't > think getting the time right is important. And even more obvious is that > most people have no business reporting anything about fireball starting > and ending bearings and elevation angles. --Rob > > -Original Message- > From: Meteorite-list [mailto:meteorite-list-boun...@meteoritecentral.com] On > Behalf Of Marco Langbroek via Meteorite-list > Sent: Wednesday, November 04, 2015 12:06 AM > To: meteorite-list@meteoritecentral.com; baa...@zagami.jpl.nasa.gov > Subject: Re: [meteorite-list] Very Bright Fireball Over Europe on Halloween > Night > >> A lot of folks say it looked green to them, which means it may have been >> metallic; > > > It is a perpetuated misunderstanding that meteor colours are primarily due > to > their composition. It's a science myth inspired by High School Bunsen burner > > experiments that appears hard to kill. > > While composition in some cases does have some influence on the colour, it > is > actually the composition of the atmosphere that is usually dominant for our > perception of meteor colours. > > That certainly is true for green colours. Meteor spectra show that meteors > usually are very strong at the "forbidden" Oxygen line at 5577 Angstrom > (557.7 > nm). This line is due to atmospheric Oxygen, the same atmospheric Oxygen > exitation line also responsible for the green colours of Aurora. > > So green meteor colours are likely atmospheric in origin and say little > about > the meteoroids' composition. > > - Marco > > - > Dr Marco (asteroid 183294) Langbroek > Dutch Meteor Society (DMS) > > e-mail: d...@marcolangbroek.nl > http://www.marcolangbroek.nl > > __ > > Visit our Facebook page https://www.facebook.com/meteoritecentral and the > Archives at http://www.meteorite-list-archives.com > Meteorite-list mailing list > Meteorite-list@meteoritecentral.com > https://pairlist3.pair.net/mailman/listinfo/meteorite-list > > __ > > Visit our Facebook page https://www.facebook.com/meteoritecentral and the > Archives at http://www.meteorite-list-archives.com > Meteorite-list mailing list > Meteorite-list@meteoritecentral.com > https://pairlist3.pair.net/mailman/listinfo/meteorite-list __ Visit our Facebook page https://www.facebook.com/meteoritecentral and the Archives at http://www.meteorite-list-archives.com Meteorite-list mailing list Meteorite-list@meteoritecentral.com https://pairlist3.pair.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] Very Bright Fireball Over Europe on Halloween Night
Rob, Marco, OK, so color isn't important. But why the different colors? Not green can't mean no oxygen. Is the green overwhelmed by other colors? Why? - John John Kashuba Bend, Oregon -Original Message- From: Meteorite-list [mailto:meteorite-list-boun...@meteoritecentral.com] On Behalf Of Rob Matson via Meteorite-list Sent: Wednesday, November 04, 2015 12:54 AM To: 'meteorite-list' Subject: Re: [meteorite-list] Very Bright Fireball Over Europe on Halloween Night HI All, Marco took the words out of my mouth. Getting tired of hearing that a green meteor tells you anything about its composition. I know that it's natural for people to think the most important thing they can report about a meteor is its color, but I wish various broadcast media would do the public a service and disabuse them of this notion. It would be far better if witnesses could be trained to get in the habit of counting the duration accurately, and noting the exact time of the meteor to the nearest minute. Seeing as how almost everyone has a cell phone these days, and all cell phones have accurate clocks, there really is no excuse to get the time wrong. Yet even a casual browse of the AMS fireball site reveals that people clearly don't think getting the time right is important. And even more obvious is that most people have no business reporting anything about fireball starting and ending bearings and elevation angles. --Rob -Original Message- From: Meteorite-list [mailto:meteorite-list-boun...@meteoritecentral.com] On Behalf Of Marco Langbroek via Meteorite-list Sent: Wednesday, November 04, 2015 12:06 AM To: meteorite-list@meteoritecentral.com; baa...@zagami.jpl.nasa.gov Subject: Re: [meteorite-list] Very Bright Fireball Over Europe on Halloween Night > A lot of folks say it looked green to them, which means it may have been > metallic; It is a perpetuated misunderstanding that meteor colours are primarily due to their composition. It's a science myth inspired by High School Bunsen burner experiments that appears hard to kill. While composition in some cases does have some influence on the colour, it is actually the composition of the atmosphere that is usually dominant for our perception of meteor colours. That certainly is true for green colours. Meteor spectra show that meteors usually are very strong at the "forbidden" Oxygen line at 5577 Angstrom (557.7 nm). This line is due to atmospheric Oxygen, the same atmospheric Oxygen exitation line also responsible for the green colours of Aurora. So green meteor colours are likely atmospheric in origin and say little about the meteoroids' composition. - Marco - Dr Marco (asteroid 183294) Langbroek Dutch Meteor Society (DMS) e-mail: d...@marcolangbroek.nl http://www.marcolangbroek.nl __ Visit our Facebook page https://www.facebook.com/meteoritecentral and the Archives at http://www.meteorite-list-archives.com Meteorite-list mailing list Meteorite-list@meteoritecentral.com https://pairlist3.pair.net/mailman/listinfo/meteorite-list __ Visit our Facebook page https://www.facebook.com/meteoritecentral and the Archives at http://www.meteorite-list-archives.com Meteorite-list mailing list Meteorite-list@meteoritecentral.com https://pairlist3.pair.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] Very Bright Fireball Over Europe on Halloween Night
The whole issue of meteor color is complex. We now have many examples of high resolution meteor spectra... but "color" is a physiological phenomenon that isn't always easy to relate to physical spectra. The light of meteors consists mostly of thermally broadened atomic emission lines- lots of them- from both the meteoritic material and the atmosphere. As has been noted, the atmospheric contributions tend to dominate. But there are often strong lines from meteoritic material, as well. In the case of large fireballs (where we have much less spectroscopic data) there may be a blackbody contribution as well, either from the ablating surface or from a supercompressed plasma. And since this is mostly driven by thermal effects, the speed of the body makes a big difference in perceived color. Throw into all of this the complexities of human vision- differences in retinal response, persistence effects, psychological effects given typically short observation times- and it's little wonder this entire area remains poorly understood. After large fireballs, when I get many witness reports submitted, I review color. It's common for about half the witnesses who report color to agree on one in particular (green is by far the most common), while the other half see red, orange, yellow, or blue. My takeaway is that we should generally assume that most color is coming from atmospheric contributions, probably modified slightly by meteoritic components (often too subtly for people to report accurately), and that above all, it's almost impossible to make any assumptions about meteoroid composition from color. Chris *** Chris L Peterson Cloudbait Observatory http://www.cloudbait.com On 11/4/2015 5:21 AM, Beatty, Kelly via Meteorite-list wrote: Marco, Rob... this discussion is timely. what you've noted is exactly my understanding. just yesterday I came across a high-profile blog about these fireballs, and the writer stated that most of the light comes from the superheated vaporized particle as it ablates. suspecting this was wrong, I looked in several places for the correct information -- IMO, AMS, RASC Handbook, etc -- and yet I didn't really find the physics spelled out explicitly. (maybe I was looking in the wrong places?) the closest I came was this post by Peter Jenniskens (http://leonid.arc.nasa.gov/meteor.html), which was equivocal. clear skies, Kelly *** J. Kelly Beatty Senior Editor, Sky & Telescope SkyandTelescope.com (a division of F+W, a Content + eCommerce Company) 617-864-7360 x22168 @NightSkyGuy -Original Message- From: Meteorite-list [mailto:meteorite-list-boun...@meteoritecentral.com] On Behalf Of Rob Matson via Meteorite-list Sent: Wednesday, November 04, 2015 3:54 AM To: 'meteorite-list' Subject: Re: [meteorite-list] Very Bright Fireball Over Europe on Halloween Night HI All, Marco took the words out of my mouth. Getting tired of hearing that a green meteor tells you anything about its composition. I know that it's natural for people to think the most important thing they can report about a meteor is its color, but I wish various broadcast media would do the public a service and disabuse them of this notion. It would be far better if witnesses could be trained to get in the habit of counting the duration accurately, and noting the exact time of the meteor to the nearest minute. Seeing as how almost everyone has a cell phone these days, and all cell phones have accurate clocks, there really is no excuse to get the time wrong. Yet even a casual browse of the AMS fireball site reveals that people clearly don't think getting the time right is important. And even more obvious is that most people have no business reporting anything about fireball starting and ending bearings and elevation angles. --Rob -Original Message- From: Meteorite-list [mailto:meteorite-list-boun...@meteoritecentral.com] On Behalf Of Marco Langbroek via Meteorite-list Sent: Wednesday, November 04, 2015 12:06 AM To: meteorite-list@meteoritecentral.com; baa...@zagami.jpl.nasa.gov Subject: Re: [meteorite-list] Very Bright Fireball Over Europe on Halloween Night A lot of folks say it looked green to them, which means it may have been metallic; It is a perpetuated misunderstanding that meteor colours are primarily due to their composition. It's a science myth inspired by High School Bunsen burner experiments that appears hard to kill. While composition in some cases does have some influence on the colour, it is actually the composition of the atmosphere that is usually dominant for our perception of meteor colours. That certainly is true for green colours. Meteor spectra show that meteors usually are very strong at the "forbidden" Oxygen line at 5577 Angstrom (557.7 nm). This line is due to atmospheric Oxygen, the same atmo
Re: [meteorite-list] Very Bright Fireball Over Europe on Halloween Night
Marco, Rob... this discussion is timely. what you've noted is exactly my understanding. just yesterday I came across a high-profile blog about these fireballs, and the writer stated that most of the light comes from the superheated vaporized particle as it ablates. suspecting this was wrong, I looked in several places for the correct information -- IMO, AMS, RASC Handbook, etc -- and yet I didn't really find the physics spelled out explicitly. (maybe I was looking in the wrong places?) the closest I came was this post by Peter Jenniskens (http://leonid.arc.nasa.gov/meteor.html), which was equivocal. clear skies, Kelly *** J. Kelly Beatty Senior Editor, Sky & Telescope SkyandTelescope.com (a division of F+W, a Content + eCommerce Company) 617-864-7360 x22168 @NightSkyGuy -Original Message- From: Meteorite-list [mailto:meteorite-list-boun...@meteoritecentral.com] On Behalf Of Rob Matson via Meteorite-list Sent: Wednesday, November 04, 2015 3:54 AM To: 'meteorite-list' Subject: Re: [meteorite-list] Very Bright Fireball Over Europe on Halloween Night HI All, Marco took the words out of my mouth. Getting tired of hearing that a green meteor tells you anything about its composition. I know that it's natural for people to think the most important thing they can report about a meteor is its color, but I wish various broadcast media would do the public a service and disabuse them of this notion. It would be far better if witnesses could be trained to get in the habit of counting the duration accurately, and noting the exact time of the meteor to the nearest minute. Seeing as how almost everyone has a cell phone these days, and all cell phones have accurate clocks, there really is no excuse to get the time wrong. Yet even a casual browse of the AMS fireball site reveals that people clearly don't think getting the time right is important. And even more obvious is that most people have no business reporting anything about fireball starting and ending bearings and elevation angles. --Rob -Original Message- From: Meteorite-list [mailto:meteorite-list-boun...@meteoritecentral.com] On Behalf Of Marco Langbroek via Meteorite-list Sent: Wednesday, November 04, 2015 12:06 AM To: meteorite-list@meteoritecentral.com; baa...@zagami.jpl.nasa.gov Subject: Re: [meteorite-list] Very Bright Fireball Over Europe on Halloween Night > A lot of folks say it looked green to them, which means it may have > been metallic; It is a perpetuated misunderstanding that meteor colours are primarily due to their composition. It's a science myth inspired by High School Bunsen burner experiments that appears hard to kill. While composition in some cases does have some influence on the colour, it is actually the composition of the atmosphere that is usually dominant for our perception of meteor colours. That certainly is true for green colours. Meteor spectra show that meteors usually are very strong at the "forbidden" Oxygen line at 5577 Angstrom (557.7 nm). This line is due to atmospheric Oxygen, the same atmospheric Oxygen exitation line also responsible for the green colours of Aurora. So green meteor colours are likely atmospheric in origin and say little about the meteoroids' composition. - Marco - Dr Marco (asteroid 183294) Langbroek Dutch Meteor Society (DMS) e-mail: d...@marcolangbroek.nl http://www.marcolangbroek.nl __ Visit our Facebook page https://www.facebook.com/meteoritecentral and the Archives at http://www.meteorite-list-archives.com Meteorite-list mailing list Meteorite-list@meteoritecentral.com https://pairlist3.pair.net/mailman/listinfo/meteorite-list __ Visit our Facebook page https://www.facebook.com/meteoritecentral and the Archives at http://www.meteorite-list-archives.com Meteorite-list mailing list Meteorite-list@meteoritecentral.com https://pairlist3.pair.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] Very Bright Fireball Over Europe on Halloween Night
HI All, Marco took the words out of my mouth. Getting tired of hearing that a green meteor tells you anything about its composition. I know that it's natural for people to think the most important thing they can report about a meteor is its color, but I wish various broadcast media would do the public a service and disabuse them of this notion. It would be far better if witnesses could be trained to get in the habit of counting the duration accurately, and noting the exact time of the meteor to the nearest minute. Seeing as how almost everyone has a cell phone these days, and all cell phones have accurate clocks, there really is no excuse to get the time wrong. Yet even a casual browse of the AMS fireball site reveals that people clearly don't think getting the time right is important. And even more obvious is that most people have no business reporting anything about fireball starting and ending bearings and elevation angles. --Rob -Original Message- From: Meteorite-list [mailto:meteorite-list-boun...@meteoritecentral.com] On Behalf Of Marco Langbroek via Meteorite-list Sent: Wednesday, November 04, 2015 12:06 AM To: meteorite-list@meteoritecentral.com; baa...@zagami.jpl.nasa.gov Subject: Re: [meteorite-list] Very Bright Fireball Over Europe on Halloween Night > A lot of folks say it looked green to them, which means it may have been > metallic; It is a perpetuated misunderstanding that meteor colours are primarily due to their composition. It's a science myth inspired by High School Bunsen burner experiments that appears hard to kill. While composition in some cases does have some influence on the colour, it is actually the composition of the atmosphere that is usually dominant for our perception of meteor colours. That certainly is true for green colours. Meteor spectra show that meteors usually are very strong at the "forbidden" Oxygen line at 5577 Angstrom (557.7 nm). This line is due to atmospheric Oxygen, the same atmospheric Oxygen exitation line also responsible for the green colours of Aurora. So green meteor colours are likely atmospheric in origin and say little about the meteoroids' composition. - Marco - Dr Marco (asteroid 183294) Langbroek Dutch Meteor Society (DMS) e-mail: d...@marcolangbroek.nl http://www.marcolangbroek.nl __ Visit our Facebook page https://www.facebook.com/meteoritecentral and the Archives at http://www.meteorite-list-archives.com Meteorite-list mailing list Meteorite-list@meteoritecentral.com https://pairlist3.pair.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] Very Bright Fireball Over Europe on Halloween Night (2)
The recent spade of very bright fireballs is due to the Taurid meteor stream by the way, which every 5-6 years shows enhanced activity of this kind. - Marco - Dr Marco (asteroid 183294) Langbroek Dutch Meteor Society (DMS) e-mail: d...@marcolangbroek.nl http://www.dmsweb.org http://www.marcolangbroek.nl - __ Visit our Facebook page https://www.facebook.com/meteoritecentral and the Archives at http://www.meteorite-list-archives.com Meteorite-list mailing list Meteorite-list@meteoritecentral.com https://pairlist3.pair.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] Very Bright Fireball Over Europe on Halloween Night
A lot of folks say it looked green to them, which means it may have been metallic; It is a perpetuated misunderstanding that meteor colours are primarily due to their composition. It's a science myth inspired by High School Bunsen burner experiments that appears hard to kill. While composition in some cases does have some influence on the colour, it is actually the composition of the atmosphere that is usually dominant for our perception of meteor colours. That certainly is true for green colours. Meteor spectra show that meteors usually are very strong at the "forbidden" Oxygen line at 5577 Angstrom (557.7 nm). This line is due to atmospheric Oxygen, the same atmospheric Oxygen exitation line also responsible for the green colours of Aurora. So green meteor colours are likely atmospheric in origin and say little about the meteoroids' composition. - Marco - Dr Marco (asteroid 183294) Langbroek Dutch Meteor Society (DMS) e-mail: d...@marcolangbroek.nl http://www.marcolangbroek.nl - __ Visit our Facebook page https://www.facebook.com/meteoritecentral and the Archives at http://www.meteorite-list-archives.com Meteorite-list mailing list Meteorite-list@meteoritecentral.com https://pairlist3.pair.net/mailman/listinfo/meteorite-list
[meteorite-list] Very Bright Fireball Over Europe on Halloween Night
http://www.slate.com/blogs/bad_astronomy/2015/11/01/halloween_fireball_bright_meteor_over_europe.html Very Bright Fireball Over Europe Saturday Night By Phil Plait November 1, 2015 Saturday night (Halloween) at around 19:00 local time, a smallish bit of cosmic debris entered Earth's atmosphere and burned up over central Europe. It was very bright, and because it happened in the early evening, a lot of people saw it. Twitter was lit up with reports. It was seen from south Sweden, Germany, Poland, and as far east as Belarus! Impressive. Pictures and video started getting posted to YouTube and Twitter as well. Here's one of the best ones, taken from Poland, that shows the fireball quite well. [Video] As you can see, it gets bright very rapidly, leaves a nice glowing train (the technical term for the trail of glowing debris), and then you see the still-hot solid meteoroid fall away. This is typical behavior for meteors. The solid part (called the meteoroid) is moving so rapidly - usually more a few dozen kilometers per second - it rams the air in front of it violently. A compressed gas heats up, and the shocked air can reach several thousand degrees. This heats the meteoroid up, causing it to glow. The rush of air past it blows the melted material off (this is called ablation), and that leaves the glowing train. The meteoroid decelerates viciously, falls below the speed where it heats the air up, and then begins its long fall to the ground (assuming it's big enough to reach the ground). It may glow for a few more seconds, but at 40-80 km high the air is quite cold, and it cools rapidly. It may break apart, raining meteorites down over some area, or big chunks might hit as well. That last part's rare, though. Unlike movies, where they show small pieces hitting at high speed, the meteoroid(s) slows to terminal velocity, usually a couple of hundred kilometers per hour (or much slower for smaller pieces), for the rest of the trip down. [Video] This video missed the first second or two of the European event, but you can see the sky light up blue-green from it: A lot of folks say it looked green to them, which means it may have been metallic; nickel glows green when heated to incandescence, and metallic meteoroids are generally mostly iron with several percent nickel. Magnesium can be blue-green as well, and that's common in stony meteorites too. On Twitter, I got a lot of people questioning if this was related to 2015 TB145, the 600-meter asteroid/dead comet that passed Earth on Saturday. Almost certainly not; the direction it was moving doesn't line up, and the difference in time makes it unlikely as well (remember, these things are moving at 20-40 kps, and TB145 passed us many hours earlier; they were separated by hundreds of thousands of kilometers at least). [Video] This video, taken by the Polish Fireball Network, shows it moving roughly SE to NW; note the Big Dipper on the horizon. As it happens, the annual Taurid meteor shower is ramping up right now. It's possible this was related; that shower is known for its fireballs. The direction kinda sorta lines up, and the radiant of the shower (the part of the sky from which meteors appear to come) was just on or above the horizon at that time, so it's possible. But if this fireball was in fact from a chunk of metal, it wasn't related; Taurids come from an old comet and have essentially no metal. Hopefully we'll know more soon. The final question is, how big was the meteoroid? It's hard to tell. I'd guess it was less than a meter across, but that really is just a guess. Objects that small rarely survive re-entry intact, but again it depends on what they're made of. All in all, a nice example of a fireball, and a good reminder that our atmosphere does a great job protecting us from the 100 or so tons of material that hits us every day. And, of course, a reminder to look up. You never know what you might see. __ Visit our Facebook page https://www.facebook.com/meteoritecentral and the Archives at http://www.meteorite-list-archives.com Meteorite-list mailing list Meteorite-list@meteoritecentral.com https://pairlist3.pair.net/mailman/listinfo/meteorite-list
