Starship Asterisk*

by **Sam** » Sun Jul 21, 2024 6:15 pm

richard schumacher wrote: ↑Sun Jul 14, 2024 2:49 pm
Deathfleer wrote: ↑Sun Jul 14, 2024 5:43 amVery lucky guy
Indeed.

I am curious to hear whether the APOD editors had heard of the shooting before choosing the image for this day?
SInce Sundays are typically "reruns" and the process for choosing what to rerun may be to a degree automated at an earlier time,
I think it is possible and even likely that this APOD represents a coincidence, not an editorial choice.

by **Bird_Man** » Tue Jul 16, 2024 4:25 pm

shaileshs wrote: ↑Sun Jul 14, 2024 5:16 pm I am more amazed by everything else other than the galaxy and the colored lighted meteorite streak. Look at the number of objects in visible light. I'm not seeing any refraction spikes etc, so assuming every single light blob is some galaxy. Yes ? How many ? 1000s.. Seems denser than deep/ultra deep views showing dense galaxies in many other photos.

Diffraction spikes are caused by light interaction with struts holding mirrors or angular aperture (like the hexagonal mirrors in the James Webb Telescope). You usually won't have diffraction spikes with either a Catadioptric (Schmidt Cassegrain or Maksutov telescopes) or a refractor. Most of the spots could very well be stars in the Milky Way.

by **Ann** » Mon Jul 15, 2024 5:04 am

Chris Peterson wrote: ↑Sun Jul 14, 2024 1:24 pm
Ann wrote: ↑Sun Jul 14, 2024 5:44 am
It is also interesting that the lower part of the meteor's trail is yellow-green. In fact, the meteor clearly changes color during its fiery decent through the Earth's atmosphere from red to green. Why is that, Chris? Okay, it has to do with the composition of the meteor again...
The most volatile meteoroid components ablate first, with refractory materials surviving longer. This compositional change is apparent in spectroscopic images of meteors, but hard to decode in a simple RGB image. But it does show up as varying colors along the path.

I should note that the direction this meteor is moving in the image is not apparent. Do not assume it is moving from upper-left to lower-right. We may be seeing the beginning of the event and the end is off the field.

Indeed, I found a few other pictures that appear to show that meteors are typically green first, red or orange second and white or cyan-white if they explode as fireballs:

: The Leonid storm of 2001 was memorable. Two fireballs were captured during the shower. Image: Tony Hallas.

Interestingly, the "red" parts of the meteor trails are not red in Tony Hallas' image, but rather magenta. The ionized material coming off the meteor trails (FeO?) is brick-red, but the "red" parts of the meteor trails are magenta.

Ann

by **florid_snow** » Mon Jul 15, 2024 4:18 am

Chris Peterson wrote: ↑Mon Jul 15, 2024 12:24 am
Roy wrote: ↑Mon Jul 15, 2024 12:15 am Take the comparison of 3 million light years to 3 ten-thousandths of a light second - what is that for? (The latter number works out to 5.6 miles and so is probably wrong, too many decImal places, as that meteor track is most likely starting at least 50 miles up)
By my calculations 0.0003 light seconds is 56 miles. If there's any error here it's likely from the implied assumption that the telescope is pointing at the zenith. As it is likely to be pointing lower than that, the distance to the meteor is greater than the height it is moving through. So if the scope was pointed at a more realistic 45° altitude, that 56 miles would mean a distance of 79 miles, or 0.0004 light seconds.

Yep, 50-80 miles, 90-120 km, whatever units you want to use, the uncertainty in distance from pointing off-zenith is not enough to change the order-of-magnitude. For this photo, the meteor and the galaxy both emitted light for about the same amount of time relative to their distance from the camera, haha, I just think that's incredible. Each were emitting light for 3000 seconds for every light-second of distance between us.

by **Roy** » Mon Jul 15, 2024 2:05 am

Right you are, Chris Peterson. Calculator error on my part, too many decimal places.

by **Chris Peterson** » Mon Jul 15, 2024 12:24 am

Roy wrote: ↑Mon Jul 15, 2024 12:15 am Take the comparison of 3 million light years to 3 ten-thousandths of a light second - what is that for? (The latter number works out to 5.6 miles and so is probably wrong, too many decImal places, as that meteor track is most likely starting at least 50 miles up)

By my calculations 0.0003 light seconds is 56 miles. If there's any error here it's likely from the implied assumption that the telescope is pointing at the zenith. As it is likely to be pointing lower than that, the distance to the meteor is greater than the height it is moving through. So if the scope was pointed at a more realistic 45° altitude, that 56 miles would mean a distance of 79 miles, or 0.0004 light seconds.

by **Roy** » Mon Jul 15, 2024 12:15 am

“Please realize that a lot of kids read this site. It is supposed to be a layman's site. Nemiroff and Bonnell know a lot of kids read their site. There is nothing wrong with their occasional descriptions that can steer towards our kids.”
I taught kids, for 18 years, after a career in the computer business up to age 63. High school and middle school. I had a second career I never expected to have. You cannot teach them by patronizing them. Take the comparison of 3 million light years to 3 ten-thousandths of a light second - what is that for? (The latter number works out to 5.6 miles and so is probably wrong, too many decImal places, as that meteor track is most likely starting at least 50 miles up)
I don’t take issue with posed pictures, like a tree against a starscape, I just think they could be interesting, but the quirky explanations?

by **Chris Peterson** » Mon Jul 15, 2024 12:09 am

Ann wrote: ↑Sun Jul 14, 2024 5:43 pm
Chris Peterson wrote: ↑Sun Jul 14, 2024 1:24 pm
Indeed, the color is due to the composition of the meteor (and of the atmosphere). And if we had a spectroscopic data, we could say a lot about what the meteoroid was made of. But with only three broadband channels (red, green, and blue) we really don't have much information. The colors of the trail come from the recombination of ionized material ablated from the meteoroid (mostly metals) and from ionized atmospheric gases (mainly oxygen- a major player in the green we see- and nitrogen). These produce light emissions on the order of a second. Persistent trains- the material seen here drifting away from the meteor path- can last many minutes. We are not seeing dust here. Meteors can produce visible dust (often referred to as smoke), but it is only seen in daylight fireballs or late twilight meteors where it is illuminated by sunlight. The long-lasting glow of persistent trails is produced by recombination in molecules (as opposed to single atoms), with FeO being an important contributor. This is continuum emission, not single spectral lines.

In terms of color, it is almost always seen as orange. I think the red color we see here (and in the trail) is a processing artifact.
FeO, isn't that rust? Isn't that the stuff that makes Mars orange?

A Martian landscape. Picture taken by the Mars Pathfinder. Credit: NASA/JPL/CALTECH/UNIVERSITY OF ARIZONA
Ann

Rust is ferric oxide, Fe₂O₃. FeO is ferrous oxide. There are several "iron oxide" species.

by **Chris Peterson** » Mon Jul 15, 2024 12:04 am

shaileshs wrote: ↑Sun Jul 14, 2024 5:16 pm I am more amazed by everything else other than the galaxy and the colored lighted meteorite streak. Look at the number of objects in visible light. I'm not seeing any refraction spikes etc, so assuming every single light blob is some galaxy. Yes ? How many ? 1000s.. Seems denser than deep/ultra deep views showing dense galaxies in many other photos.

We only get diffraction spikes from reflector telescopes which have arms supporting a secondary mirror. This image has a FOV of 5° x 3.5°, which likely means it was made with a refractor... so no diffraction spikes.

Here's an annotated version of the image showing the locations of known galaxies in the field. There are a lot! But if you zoom in you'll find that very few are visible in this exposure, which simply doesn't go deep enough. So almost every point we see here is a star.
_

by **johnnydeep** » Sun Jul 14, 2024 5:53 pm

shaileshs wrote: ↑Sun Jul 14, 2024 5:16 pm I am more amazed by everything else other than the galaxy and the colored lighted meteorite streak. Look at the number of objects in visible light. I'm not seeing any refraction spikes etc, so assuming every single light blob is some galaxy. Yes ? How many ? 1000s.. Seems denser than deep/ultra deep views showing dense galaxies in many other photos.

I expect (and hope) Chris will weigh in here, and I suspect most of those objects are stars not galaxies, but to be more sure, we need to know exactly how this image was made and what specific images were used to compose it. After searching for 15 minutes I came up empty. I couldn't even find any further details on the author's Instagram page. Note: this APOD was originally posted in 2019.

EDIT: even in this very deep image from the VLT Survey Telescope (VST) at ESO’s Paranal Observatory in Chile, I can only clearly identify a few obvious galaxies:

https://www.eso.org/public/images/eso1424a/

But even here, it doesn't seem to mention how long the exposure(s) were.

by **Ann** » Sun Jul 14, 2024 5:43 pm

Chris Peterson wrote: ↑Sun Jul 14, 2024 1:24 pm
Indeed, the color is due to the composition of the meteor (and of the atmosphere). And if we had a spectroscopic data, we could say a lot about what the meteoroid was made of. But with only three broadband channels (red, green, and blue) we really don't have much information. The colors of the trail come from the recombination of ionized material ablated from the meteoroid (mostly metals) and from ionized atmospheric gases (mainly oxygen- a major player in the green we see- and nitrogen). These produce light emissions on the order of a second. Persistent trains- the material seen here drifting away from the meteor path- can last many minutes. We are not seeing dust here. Meteors can produce visible dust (often referred to as smoke), but it is only seen in daylight fireballs or late twilight meteors where it is illuminated by sunlight. The long-lasting glow of persistent trails is produced by recombination in molecules (as opposed to single atoms), with FeO being an important contributor. This is continuum emission, not single spectral lines.

In terms of color, it is almost always seen as orange. I think the red color we see here (and in the trail) is a processing artifact.

FeO, isn't that rust? Isn't that the stuff that makes Mars orange?

: A Martian landscape. Picture taken by the Mars Pathfinder. Credit: NASA/JPL/CALTECH/UNIVERSITY OF ARIZONA

Ann

by **shaileshs** » Sun Jul 14, 2024 5:16 pm

I am more amazed by everything else other than the galaxy and the colored lighted meteorite streak. Look at the number of objects in visible light. I'm not seeing any refraction spikes etc, so assuming every single light blob is some galaxy. Yes ? How many ? 1000s.. Seems denser than deep/ultra deep views showing dense galaxies in many other photos.

by **zendae** » Sun Jul 14, 2024 4:44 pm

Roy wrote: ↑Sun Jul 14, 2024 12:21 pm Really tired of the vapid, patronizing explanations of quirky photos. I don’t see the humor in the “meteor missed the galaxy” bit.
As to the colors of the meteor track, the velocity is sufficient to ionize atmosphere and meteor debris. Colors will vary. “Dust” looks like red sprites, which are high-atmosphere electric discharges, probably spreading all that ionization disturbance over a wider volume. One cannot pretend there are no electrical effects.

Please realize that a lot of kids read this site. It is supposed to be a layman's site. Nemiroff and Bonnell know a lot of kids read their site. There is nothing wrong with their occasional descriptions that can steer towards our kids.

by **richard schumacher** » Sun Jul 14, 2024 2:49 pm

Deathfleer wrote: ↑Sun Jul 14, 2024 5:43 amVery lucky guy

Indeed.

by **florid_snow** » Sun Jul 14, 2024 2:47 pm

What a spectacular shot! I love thinking about how the light from the galaxy is relatively constant, from an amateur instrument, M33 is always going to look the same, every night, for the rest of our lives and a long time into the future. But that meteor barely lasted a second, and you'll never see another exactly like it ever again.

Here's a quick order-of-magnitude analysis. If the meteor was about 90 km away (3 x 10^-4 light seconds) and the light emission lasts for about a second, then the ratio is 1/3 x 10^-4 = 3.3 x 10^3 seconds per light second, which is to say, the light emission filled the space between the meteor and the camera for about 3000 times longer than it took to travel the distance.

The same ratio for M33 would be 3000 x 3 million light years = 10 billion years, which is, on the hand-waving scale of order-of-magnitude analysis, kinda close to an estimate for how long M33 has been emitting light towards us. So despite the incredible difference in time-scale for both the galaxy and the meteor, they have a curious similarity in the ratio between how long they've been emitting and the distances between us.

by **Chris Peterson** » Sun Jul 14, 2024 1:24 pm

Ann wrote: ↑Sun Jul 14, 2024 5:44 am
I am of course wondering about the very red-colored dust coming off the meteor. I'd like to ask Chris why this dust is so red, but I know that he would only say that the color is due to the composition of the meteor, and since he himself knows nothing about the composition of this meteor, he can't say anything about the red-colored dust! Right, Chris?

Indeed, the color is due to the composition of the meteor (and of the atmosphere). And if we had a spectroscopic data, we could say a lot about what the meteoroid was made of. But with only three broadband channels (red, green, and blue) we really don't have much information. The colors of the trail come from the recombination of ionized material ablated from the meteoroid (mostly metals) and from ionized atmospheric gases (mainly oxygen- a major player in the green we see- and nitrogen). These produce light emissions on the order of a second. Persistent trains- the material seen here drifting away from the meteor path- can last many minutes. We are not seeing dust here. Meteors can produce visible dust (often referred to as smoke), but it is only seen in daylight fireballs or late twilight meteors where it is illuminated by sunlight. The long-lasting glow of persistent trails is produced by recombination in molecules (as opposed to single atoms), with FeO being an important contributor. This is continuum emission, not single spectral lines.

In terms of color, it is almost always seen as orange. I think the red color we see here (and in the trail) is a processing artifact.

It is also interesting that the lower part of the meteor's trail is yellow-green. In fact, the meteor clearly changes color during its fiery decent through the Earth's atmosphere from red to green. Why is that, Chris? Okay, it has to do with the composition of the meteor again...

The most volatile meteoroid components ablate first, with refractory materials surviving longer. This compositional change is apparent in spectroscopic images of meteors, but hard to decode in a simple RGB image. But it does show up as varying colors along the path.

I should note that the direction this meteor is moving in the image is not apparent. Do not assume it is moving from upper-left to lower-right. We may be seeing the beginning of the event and the end is off the field.

by **Roy** » Sun Jul 14, 2024 12:21 pm

Really tired of the vapid, patronizing explanations of quirky photos. I don’t see the humor in the “meteor missed the galaxy” bit.
As to the colors of the meteor track, the velocity is sufficient to ionize atmosphere and meteor debris. Colors will vary. “Dust” looks like red sprites, which are high-atmosphere electric discharges, probably spreading all that ionization disturbance over a wider volume. One cannot pretend there are no electrical effects.

by **Ann** » Sun Jul 14, 2024 5:44 am

The APOD looks positively unreal!

: Meteor Misses Galaxy. Credit & Copyright: Aman Chokshi

: A collage of astronomical and astronomy-related images.

The APOD looks as if it was cut in half, and as if the meteor trail was the dividing line. It looks as if the lower left and upper right part of the image were not part of the same frame at all! It looks as if it was a collage consisting of two images! What a fantastic, and lucky, shot!

I am of course wondering about the very red-colored dust coming off the meteor. I'd like to ask Chris why this dust is so red, but I know that he would only say that the color is due to the composition of the meteor, and since he himself knows nothing about the composition of this meteor, he can't say anything about the red-colored dust! Right, Chris?

It is also interesting that the lower part of the meteor's trail is yellow-green. In fact, the meteor clearly changes color during its fiery decent through the Earth's atmosphere from red to green. Why is that, Chris? Okay, it has to do with the composition of the meteor again...

It said in the caption that the photographer, Aman Choksi, took this image as well as two other images of M33 to bring out the galaxy's colors. This, of course, made me go hunting for a good image of M33 that really brings out the galaxy's colors. Among the images I found by googling, I decided that this one was the best one:

M33. Credit: Cosgrove's Cosmos.

Some interesting NGC, IC and PGC objects in and near M33.

You have to go to Patrick Cosgrove's website and watch the full size of his image! Amazing!

Ann

by **Deathfleer** » Sun Jul 14, 2024 5:43 am

Very lucky guy

by **APOD Robot** » Sun Jul 14, 2024 4:06 am

Meteor Misses Galaxy

Explanation: The galaxy was never in danger. For one thing, the Triangulum galaxy (M33), pictured, is much bigger than the tiny grain of rock at the head of the meteor. For another, the galaxy is much farther away -- in this instance 3 million light years as opposed to only about 0.0003 light seconds. Even so, the meteor's path took it angularly below the galaxy. Also the wind high in Earth's atmosphere blew the meteor's glowing evaporative molecule train away from the galaxy, in angular projection. Still, the astrophotographer was quite lucky to capture both a meteor and a galaxy in a single exposure -- which was subsequently added to two other images of M33 to bring up the spiral galaxy's colors. At the end, the meteor was gone in a second, but the galaxy will last billions of years.

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