APOD: A Meteor and the Gegenschein (2021 May 12)

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APOD: A Meteor and the Gegenschein (2021 May 12)

Post by APOD Robot » Wed May 12, 2021 4:07 am

Image A Meteor and the Gegenschein

Explanation: Is the night sky darkest in the direction opposite the Sun? No. In fact, a rarely discernable faint glow known as the gegenschein (German for "counter glow") can be seen 180 degrees around from the Sun in an extremely dark sky. The gegenschein is sunlight back-scattered off small interplanetary dust particles. These dust particles are millimeter sized splinters from asteroids and orbit in the ecliptic plane of the planets. Pictured here from last March is one of the more spectacular pictures of the gegenschein yet taken. The deep exposure of an extremely dark sky over Teide Observatory in Spain's Canary Islands shows the gegenschein as part of extended zodiacal light. Notable background objects include a bright meteor (on the left), the Big Dipper (top right), and Polaris (far right). The meteor nearly points toward Mount Teide, Spain's highest mountain, while the Pyramid solar laboratory is visible on the right. During the day, a phenomenon like the gegenschein called the glory can be seen in reflecting air or clouds opposite the Sun from an airplane.

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Re: APOD: A Meteor and the Gegenschein (2021 May 12)

Post by Ann » Wed May 12, 2021 4:55 am

That's a really fascinating image! Thanks! :D


For me the picture is frustrating, too, as I can't make sense of the background stars. I think that the little cluster we can see at the bottom of the column of the Gegenschein is M44, the Beehive Cluster in Cancer. But if so, Leo should be nearby - but not too nearby! - and I can't find it where I think it ought to be.

Can anyone help me?

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Re: APOD: A Meteor and the Gegenschein (2021 May 12)

Post by alter-ego » Wed May 12, 2021 5:14 am

Ann wrote:
Wed May 12, 2021 4:55 am
That's a really fascinating image! Thanks! :D


For me the picture is frustrating, too, as I can't make sense of the background stars. I think that the little cluster we can see at the bottom of the column of the Gegenschein is M44, the Beehive Cluster in Cancer. But if so, Leo should be nearby - but not too nearby! - and I can't find it where I think it ought to be.

Can anyone help me?

Ann
The Beehive is correct. Leo is directly over the cluster. The lion's back is parallel (and within) the Zodiacal light. Regulus is the bright star in the Zodiacal light about midway between the Beehive and Gegenschein. Pollux and Castor are behind the observatory near the horizon.
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Re: APOD: A Meteor and the Gegenschein (2021 May 12)

Post by Chris Peterson » Wed May 12, 2021 5:26 am

APOD Robot wrote:
Wed May 12, 2021 4:07 am
The gegenschein is sunlight back-scattered off small interplanetary dust particles. These dust particles are millimeter sized splinters from asteroids and orbit in the ecliptic plane of the planets.
This band of interplanetary dust particles also produces the zodiacal light- typically seen as forward scattered light in the direction of the Sun after sunset or before sunrise. New evidence suggests that these particles are not produced by asteroids, but are associated with Mars, although the ejection mechanism remains uncertain.
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Re: APOD: A Meteor and the Gegenschein (2021 May 12)

Post by Ann » Wed May 12, 2021 7:10 am

alter-ego wrote:
Wed May 12, 2021 5:14 am
Ann wrote:
Wed May 12, 2021 4:55 am

For me the picture is frustrating, too, as I can't make sense of the background stars. I think that the little cluster we can see at the bottom of the column of the Gegenschein is M44, the Beehive Cluster in Cancer. But if so, Leo should be nearby - but not too nearby! - and I can't find it where I think it ought to be.

Can anyone help me?

Ann
The Beehive is correct. Leo is directly over the cluster. The lion's back is parallel (and within) the Zodiacal light. Regulus is the bright star in the Zodiacal light about midway between the Beehive and Gegenschein. Pollux and Castor are behind the observatory near the horizon.
Gegenschein Big Dipper and Beehive annotated J S Casado.png

Thank you, alter-ego!

I've tried to annotate the APOD a bit. I have filled in the Big Dipper and made a ring around Polaris.

I've also made a ring around Regulus and drawn a figure "1" above it. "2" is the Beehive cluster.

I still can't see the Sickle of Leo.

Ann
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Last edited by Ann on Wed May 12, 2021 9:13 am, edited 1 time in total.
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Re: APOD: A Meteor and the Gegenschein (2021 May 12)

Post by rj rl » Wed May 12, 2021 7:33 am

Thanks, Ann! I couldn't even make out the Big Dipper, surprised how little it stands out.

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Re: APOD: A Meteor and the Gegenschein (2021 May 12)

Post by Ann » Wed May 12, 2021 10:21 am

Chris Peterson wrote:
Wed May 12, 2021 5:26 am
APOD Robot wrote:
Wed May 12, 2021 4:07 am
The gegenschein is sunlight back-scattered off small interplanetary dust particles. These dust particles are millimeter sized splinters from asteroids and orbit in the ecliptic plane of the planets.
This band of interplanetary dust particles also produces the zodiacal light- typically seen as forward scattered light in the direction of the Sun after sunset or before sunrise. New evidence suggests that these particles are not produced by asteroids, but are associated with Mars, although the ejection mechanism remains uncertain.
Check out this video:

Click to play embedded YouTube video.

Note that the zodiacal light and the gegenschein are caused by the same phenomenon, sunlight reflected by tiny dust particles in the orbital plane of the Solar system.

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Re: APOD: A Meteor and the Gegenschein (2021 May 12)

Post by orin stepanek » Wed May 12, 2021 11:22 am

GegenscheinBolide_Casado_1080_annotated.jpg
Very nice discussion by everyone; I like the way everybody explained
the starry sky! Beautiful annotation by APOD! :thumb_up: This could be a
nice background!:wink:
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Re: APOD: A Meteor and the Gegenschein (2021 May 12)

Post by neufer » Wed May 12, 2021 2:53 pm

https://en.wikipedia.org/wiki/Mojave_(crater) wrote:
Click to play embedded YouTube video.

<<Mojave is a 58 km diameter impact crater in the Oxia Palus quadrangle of Mars. The crater is located at 7.5° N and 33.0° W within the Martian Xanthe Terra region. Some parts of the crater display a high concentration of closely spaced pits. Pits show little or no evidence of rims or ejecta. The pits are so close to each other that adjacent pits often share the same wall. It is believed that the pits form from steam produced when the heat from the impact process interacts with ice in the ground. Mojave is a rayed crater, another indication of its youth, and is the largest such crater on Mars. Based on crater counts of its ejecta blanket, it is thought to be about 3 million years old. It is believed to be the most recent crater of its size on Mars, and has been identified as the probable source of the shergottite meteorites collected on Earth.

The depth of Mojave is approximately 2,600 meters. Based on its ratio of depth to diameter, researchers believe it is very young. It is not old enough to have accumulated much material and start to fill. Its relatively undegraded state helps scientists model impact processes on Mars. If one measures the diameter of a crater, the original depth can be estimated with various ratios. Because of this relationship, researchers have found that many Martian craters contain a great deal of material; much of it is believed to be ice deposited when the climate was different.>>
https://en.wikipedia.org/wiki/Asteroid_belt wrote:
Click to play embedded YouTube video.

<<The high population of the asteroid belt makes for a very active environment, where collisions between asteroids occur frequently (on astronomical time scales). Collisions between main-belt bodies with a mean radius of 10 km are expected to occur about once every 10 million years. A collision may fragment an asteroid into numerous smaller pieces (leading to the formation of a new asteroid family).

Along with the asteroid bodies, the asteroid belt also contains bands of dust with particle radii of up to a few hundred micrometres. This fine material is produced, at least in part, from collisions between asteroids, and by the impact of micrometeorites upon the asteroids. Due to the Poynting–Robertson effect, the pressure of solar radiation causes this dust to slowly spiral inward toward the Sun.

The combination of this fine asteroid dust, as well as ejected cometary material, produces the zodiacal light. Asteroid particles that produce the visible zodiacal light average about 40 μm in radius. The typical lifetimes of main-belt zodiacal cloud particles are about 700,000 years. Thus, to maintain the bands of dust, new particles must be steadily produced within the asteroid belt. It was once thought that collisions of asteroids form a major component of the zodiacal light. However, computer simulations by Nesvorný and colleagues attributed 85 percent of the zodiacal-light dust to fragmentations of Jupiter-family comets, rather than to comets and collisions between asteroids in the asteroid belt. At most 10 percent of the dust is attributed to the asteroid belt.>>
https://en.wikipedia.org/wiki/Martian_meteorite#Shergottites wrote:
<<Roughly three-quarters of all Martian meteorites can be classified as shergottites. They are named after the Shergotty meteorite, which fell at Sherghati, India in 1865. Shergottites are igneous rocks of mafic to ultramafic lithology. They fall into three main groups, the basaltic, olivine-phyric (such as the Tissint group found in Morocco in 2011) and Lherzolitic shergottites, based on their crystal size and mineral content. They can be categorised alternatively into three or four groups based on their rare-earth element content. These two classification systems do not line up with each other, hinting at complex relationships between the various source rocks and magmas from which the shergottites formed.>>
https://en.wikipedia.org/wiki/Tissint_meteorite wrote: <<On July 18, 2011, around 2 AM local time, a bright fireball was observed by several people in the Oued Drâa valley, east of Tata, Morocco. One observer reported that the fireball was initially yellow in color, then turned green, illuminating the entire area before it appeared to break into two pieces; two sonic booms were heard over the valley. In October 2011, nomads began to find very fresh, fusion-crusted stones in a remote area of the Oued Drâa intermittent watershed. The Tissint meteorite was named after the town of Tissint, 48 kilometres away from the fall site. Dozens of fragments with masses ranging from 0.2 to 1,282 grams were collected, totaling roughly 12–15 kilograms.

The meteorite was ejected from the surface of Mars between 700,000 and 1.1 million years ago. Tissint appears to be derived from a deep mantle source region that was unlike any of the other known Martian shergottite meteorites. The material is highly shocked and indicates it was ejected during the largest impact excavation in record. Given the widely dispersed shock melting observed in Tissint, alteration of other soft minerals (carbonates, halides, sulfates and even organics), especially along grain boundaries, might have occurred. This may in part explain the lack of such minerals in Tissint, but it is unknown if it is of biotic origin.

The meteorite fragments were recovered within days after the fall, so it is considered an "uncontaminated" meteorite. The meteorite displays evidence of water weathering, and there are signs of elements being carried into cracks in the rocks by water or fluid, which is something never seen before in a Martian meteorite. Specifically, scientists found carbon and nitrogen-containing compounds associated with hydrothermal mineral inclusions. One team reported measuring an elevated carbon-13 ratio, while another team reported a low 13C ratio as compared to the content in Mars' atmosphere and crust, and suggested that it may be of biological origin, but the researchers also noted that there are several geological processes that could explain that without invoking complex life-processes; for example, it could be of meteoritic origin and would have been mixed with Martian soil when meteorites and comets impact the surface of Mars, or of volcanic origin.

The data on refractory trace elements, sulfur and fluorine as well as the data on the isotopic composition of nitrogen, argon and carbon released upon heating from the matrix and glass veins in the meteorite unambiguously indicate the presence of a Martian surface component including trapped atmospheric gases. So, the influence of in situ Martian weathering can be distinguished from terrestrial contamination in the meteorite. The Martian weathering features in Tissint are compatible with the results of spacecraft observations of Mars, and Tissint has a cosmic ray dating exposure age of 0.7 ± 0.3 Ma—consistent with the reading of many other shergottites, notably EETA79001, suggesting that they were ejected from Mars during the same event.

The overall composition of the Tissint meteorite corresponds to that of aluminium-poor ferroan basaltic rock, which likely originated as a result of magmatic activity at the surface of Mars. These basalt then underwent weathering by fluids, which deposited minerals enriched in incompatible elements in fissures and cracks. A later impact on the surface of Mars melted the leached material forming black glassy veins. Finally shergottites were ejected from Mars about 0.7 million years ago.>>
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Re: APOD: A Meteor and the Gegenschein (2021 May 12)

Post by Chris Peterson » Wed May 12, 2021 3:14 pm

neufer wrote:
Wed May 12, 2021 2:53 pm

Mojave is a 58 km diameter impact crater... (and lots of other stuff).
Umm... your point?
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Re: APOD: A Meteor and the Gegenschein (2021 May 12)

Post by neufer » Wed May 12, 2021 3:33 pm

Chris Peterson wrote:
Wed May 12, 2021 3:14 pm
neufer wrote:
Wed May 12, 2021 2:53 pm

Mojave is a 58 km diameter impact crater... (and lots of other stuff).
Umm... your point?
Gegenschein & Zodiacal particles consist primarily of
the remnants of the (0.7 to 3.0 million years old) Mojave impact.

Mars Pathfinder panorama (with Mojave debris field?) & the Sojourner rover.
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Re: APOD: A Meteor and the Gegenschein (2021 May 12)

Post by Chris Peterson » Wed May 12, 2021 3:41 pm

neufer wrote:
Wed May 12, 2021 3:33 pm
Chris Peterson wrote:
Wed May 12, 2021 3:14 pm
neufer wrote:
Wed May 12, 2021 2:53 pm

Mojave is a 58 km diameter impact crater... (and lots of other stuff).
Umm... your point?
Gegenschein & Zodiacal particles consist primarily of
the remnants of the (0.7 to 3.0 million years old) Mojave impact.

Mars Pathfinder panorama (with Mojave debris field?) & the Sojourner rover.
Maybe. Material ejected from Phobos or Deimos is also a candidate. As is material raised by dust storms high enough to be ejected by solar wind. I'd say the jury is still out.
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Re: APOD: A Meteor and the Gegenschein (2021 May 12)

Post by johnnydeep » Wed May 12, 2021 6:45 pm

Interesting tidbit from the WikiPedia page on Teide Observatory - https://en.wikipedia.org/wiki/Teide_Obs ... n_the_site :
Other buildings on the site
The observatory has a visitors' centre and a residencia (hostel) for astronomers. Brian May helped construct a building there to study interplanetary dust.
Brian May as we all should know, is an astrophysicist who also happens to be a founding member and lead guitarist of the rock band Queen!
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Re: APOD: A Meteor and the Gegenschein (2021 May 12)

Post by MarkBour » Wed May 12, 2021 7:17 pm

I wonder if the gegenschein is more clearly visible while in outer space. I wonder if the inhabitants of the ISS have ever photographed it.
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Re: APOD: A Meteor and the Gegenschein (2021 May 12)

Post by neufer » Wed May 12, 2021 10:36 pm

Chris Peterson wrote:
Wed May 12, 2021 3:41 pm
neufer wrote:
Wed May 12, 2021 3:33 pm
Chris Peterson wrote:
Wed May 12, 2021 3:14 pm

Umm... your point?
Gegenschein & Zodiacal particles consist primarily of
the remnants of the (0.7 to 3.0 million years old) Mojave impact.

Mars Pathfinder panorama (with Mojave debris field?) & the Sojourner rover.
Maybe. Material ejected from Phobos or Deimos is also a candidate. As is material raised by dust storms high enough to be ejected by solar wind. I'd say the jury is still out.
  • I'm just happy that my very specific suggestion hasn't been shot down already. :)
Here is the problem, IMO:
  • 1) Mars's escape velocity is 5 km/s!

    2) Phobos's 'average' escape velocity is 3 km/s.

    3) Even at the distance of Deimos, Mars's gravity is
    30X the force of solar radiation on even 10 μm dust.

    4) The interplanetary dust cloud is more massive than Phobos & Deimos combined.
  • Phobos Mean radius: 11.3 km
    Deimos Mean radius: 6.2 km
https://en.wikipedia.org/wiki/Interplanetary_dust_cloud wrote:
<<The total mass of the interplanetary dust cloud is approximately the mass of an asteroid of radius 15 km. Straddling the zodiac along the ecliptic, this dust cloud is visible as the zodiacal light in a moonless and naturally dark sky and is best seen sunward during astronomical twilight.>>
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Re: APOD: A Meteor and the Gegenschein (2021 May 12)

Post by neufer » Thu May 13, 2021 12:05 am

MarkBour wrote:
Wed May 12, 2021 7:17 pm

I wonder if the gegenschein is more clearly visible while in outer space.

I wonder if the inhabitants of the ISS have ever photographed it.
https://www.theguardian.com/science/2015/nov/15/international-space-station-astronaut-starwatching wrote:
<<Unfortunately... the space station itself is a significant source of light pollution for the [ISS] crew, making it extremely difficult to take good pictures of the dim astronomical objects. In a suitable location, Earth-bound observers will actually have quite an advantage over astronauts observing stars and deep-space objects: the vantage point may not be quite as exotic, but a dedicated astrophotographer can still capture something unique.>>
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Re: APOD: A Meteor and the Gegenschein (2021 May 12)

Post by Chris Peterson » Thu May 13, 2021 1:08 am

neufer wrote:
Thu May 13, 2021 12:05 am
MarkBour wrote:
Wed May 12, 2021 7:17 pm

I wonder if the gegenschein is more clearly visible while in outer space.

I wonder if the inhabitants of the ISS have ever photographed it.
https://www.theguardian.com/science/2015/nov/15/international-space-station-astronaut-starwatching wrote:
<<Unfortunately... the space station itself is a significant source of light pollution for the [ISS] crew, making it extremely difficult to take good pictures of the dim astronomical objects. In a suitable location, Earth-bound observers will actually have quite an advantage over astronauts observing stars and deep-space objects: the vantage point may not be quite as exotic, but a dedicated astrophotographer can still capture something unique.>>
And aside from that, the atmospheric attenuation of visible light is very low at the zenith. Even without having windows or space helmets to deal with, the view of the sky from space isn't much different than from a good dark site on the ground.
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Re: APOD: A Meteor and the Gegenschein (2021 May 12)

Post by neufer » Thu May 13, 2021 2:53 am

Chris Peterson wrote:
Thu May 13, 2021 1:08 am

And aside from that, the atmospheric attenuation Gvisible light is very low at the zenith. Even without having windows or space helmets to deal with, the view of the sky from space isn't much different than from a good dark site on the ground.
https://earthsky.org/space/definition-what-is-the-gegenschein wrote:
What is the gegenschein?
by EarthSky Voices in Astronomy Essentials | Space | March 10,

<<The gegenschein cannot be seen from light-polluted sites. Even moderate light pollution diminishes the counterglow’s contrast way too much. Based on our observations, the absolute minimum to detect the gegenschein is a sky brightness of 21.0 mag/arcsecond2 in the zenith. But this applies only if you are already quite familiar with the gegenschein and know exactly what and where to look for. For first-time observers we recommend a site with a sky brightness of 21.2 mag/arcsecond2 in the zenith or better. Observing sites in the mountains especially qualify because of the reduced air mass at higher altitudes above sea level.>>
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Re: APOD: A Meteor and the Gegenschein (2021 May 12)

Post by Chris Peterson » Thu May 13, 2021 4:42 am

neufer wrote:
Thu May 13, 2021 2:53 am
Chris Peterson wrote:
Thu May 13, 2021 1:08 am

And aside from that, the atmospheric attenuation Gvisible light is very low at the zenith. Even without having windows or space helmets to deal with, the view of the sky from space isn't much different than from a good dark site on the ground.
  • So, Chris, have you, yourself, seen (or, at least, photographed) gegenschein :?:
I have seen it many times. Never imaged it, though. It's actually pretty bright, and not all that hard to see from any decently dark site.
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Re: APOD: A Meteor and the Gegenschein (2021 May 12)

Post by neufer » Thu May 13, 2021 1:33 pm

Chris Peterson wrote:
Thu May 13, 2021 4:42 am
neufer wrote:
Thu May 13, 2021 2:53 am
Chris Peterson wrote:
Thu May 13, 2021 1:08 am

And aside from that, the atmospheric attenuation Gvisible light is very low at the zenith. Even without having windows or space helmets to deal with, the view of the sky from space isn't much different than from a good dark site on the ground.
  • So, Chris, have you, yourself, seen (or, at least, photographed) gegenschein :?:
I have seen it many times. Never imaged it, though.

It's actually pretty bright, and not all that hard to see from any decently dark site.
That's not what I've read: http://adsabs.harvard.edu/full/1899PA......7..169B
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Re: APOD: A Meteor and the Gegenschein (2021 May 12)

Post by Chris Peterson » Thu May 13, 2021 1:37 pm

neufer wrote:
Thu May 13, 2021 1:33 pm
Chris Peterson wrote:
Thu May 13, 2021 4:42 am
neufer wrote:
Thu May 13, 2021 2:53 am
  • So, Chris, have you, yourself, seen (or, at least, photographed) gegenschein :?:
I have seen it many times. Never imaged it, though.

It's actually pretty bright, and not all that hard to see from any decently dark site.
That's not what I've read: http://adsabs.harvard.edu/full/1899PA......7..169B
It's not what I've read, either. But the reality is, I haven't found it difficult to see. A couple of times I've seen it connected to a band of zodiacal light.
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Re: APOD: A Meteor and the Gegenschein (2021 May 12)

Post by bystander » Thu May 13, 2021 3:41 pm

johnnydeep wrote:
Wed May 12, 2021 6:45 pm
Interesting tidbit from the WikiPedia page on Teide Observatory - https://en.wikipedia.org/wiki/Teide_Obs ... n_the_site :
Other buildings on the site
The observatory has a visitors' centre and a residencia (hostel) for astronomers. Brian May helped construct a building there to study interplanetary dust.
Brian May as we all should know, is an astrophysicist who also happens to be a founding member and lead guitarist of the rock band Queen!
Brian May was working on his PhD dissertation at Imperial College London in 1974 when the international popularity of Queen began to take off. He abandoned his doctoral studies until 2006 when he re-registered. He submitted his doctoral thesis, A Survey of Radial Velocities in the Zodiacal Dust Cloud, in 2007, receiving his PhD in 2008. He was only able to submit his revised thesis on his 37 year old research into the Zodiacal Light and Zodiacal Dust Cloud because of the scarcity of research on the subject in the intervening years.
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Re: APOD: A Meteor and the Gegenschein (2021 May 12)

Post by johnnydeep » Thu May 13, 2021 3:55 pm

bystander wrote:
Thu May 13, 2021 3:41 pm
johnnydeep wrote:
Wed May 12, 2021 6:45 pm
Interesting tidbit from the WikiPedia page on Teide Observatory - https://en.wikipedia.org/wiki/Teide_Obs ... n_the_site :
Other buildings on the site
The observatory has a visitors' centre and a residencia (hostel) for astronomers. Brian May helped construct a building there to study interplanetary dust.
Brian May as we all should know, is an astrophysicist who also happens to be a founding member and lead guitarist of the rock band Queen!
Brian May was working on his PhD dissertation at Imperial College London in 1974 when the international popularity of Queen began to take off. He abandoned his doctoral studies until 2006 when he re-registered. He submitted his doctoral thesis, A Survey of Radial Velocities in the Zodiacal Dust Cloud, in 2007, receiving his PhD in 2008. He was only able to submit his revised thesis on his 37 year old research into the Zodiacal Light and Zodiacal Dust Cloud because of the scarcity of research on the subject in the intervening years.
Cool! So, Brian May is even more relevant to this APOD discussion that I realized!
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