APOD: Solstice Conjunction over Budapest (2017 Jun 23)

[APOD Robot]

Solstice Conjunction over Budapest

Explanation: Before a solstice Sun rose on June 21, brilliant Venus and an old crescent Moon posed together over Budapest, Hungary for this predawn skyscape. In the foreground the view looks across the Danube river from Buda to Pest toward the dome and peaks of the Hungarian Parliament building. Low clouds are in silhouette against a twilight sky. But far enough above the eastern horizon to catch the sunlight shines another seasonal apparition on that solstice morning, noctilucent clouds. Seen near sunrise and sunset in summer months at high latitudes, the night-shining clouds are formed as water vapor in the cold upper atmosphere condenses on meteoric dust or volcanic ash near the edge of space.

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[neufer]

[b][color=#0000FF]Noctilucent clouds photographed by the crew of the ISS[/color][/b]

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<<Night clouds or noctilucent clouds are composed of tiny crystals of water ice up to 100 nm in diameter and exist at a height of about 76 to 85 km. (On August 28, 2006, scientists with the Mars Express mission announced that they found clouds of carbon dioxide crystals over Mars that extended up to 100 km above the surface of the planet; they are the highest clouds discovered over the surface of a planet.) Noctilucent clouds may be seen by observers at a latitude of 50° to 65°. They seldom occur at lower latitudes (e.g., Budapest: 47°30′N), and closer to the poles it does not get dark enough for the clouds to become visible. The characteristic blue colour comes from absorption by ozone in the path of the sunlight illuminating the noctilucent cloud. They occur during summer, from mid-May to mid-August in the northern hemisphere and between mid-November and mid-February in the southern hemisphere.>>

[Chris Peterson]

Night clouds or noctilucent clouds are composed of tiny crystals of water ice up to 100 nm in diameter and exist at a height of about 76 to 85 km...

Also interesting (at least to a meteor scientist like me) is the fact that these clouds appear to seed on dust which is largely created by the disintegration of meteoritic particles in the upper atmosphere. Shooting stars seed noctilucent clouds.

[neufer]

[b][color=#0000FF][size=150]Noctilucent Cloud visible over Orlando formed by a Falcon 9 about 90 minutes after August 2014 lift off.[/size][/color][/b]

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Also interesting (at least to a meteor scientist like me) is the fact that these clouds appear to seed on dust which is largely created by the disintegration of meteoritic particles in the upper atmosphere.

Shooting stars seed noctilucent clouds.

[Chris Peterson]

Also interesting (at least to a meteor scientist like me) is the fact that these clouds appear to seed on dust which is largely created by the disintegration of meteoritic particles in the upper atmosphere.

Shooting stars seed noctilucent clouds.

Noctilucent Cloud visible over Orlando formed by a Falcon 9 about 90 minutes after August 2014 lift off.

You need dust, and you need water. Most of the dust in the upper atmosphere comes from meteors, but there are other sources, particularly volcanic eruptions. Where the water comes from is less clear, but one definite source is the vapor from rocket launches. This launch isn't what's seeding the noctilucent clouds- that's still meteoritic dust. The launch is providing the water.

[neufer]

You need dust, and you need water. Most of the dust in the upper atmosphere comes from meteors, but there are other sources, particularly volcanic eruptions. Where the water comes from is less clear, but one definite source is the vapor from rocket launches. This launch isn't what's seeding the noctilucent clouds- that's still meteoritic dust. The launch is providing the water.

• Are you sure That would seem to be quite inefficient.

<<Falcon 9 is a family of two-stage-to-orbit launch vehicles. Both stages are powered by rocket engines that burn liquid oxygen (LOX) and rocket-grade kerosene (RP-1) propellants. (The first stage is designed to be reusable, while the second stage is not.)>>

<<Chemically, a hydrocarbon propellant (like RP-1) is less efficient than hydrogen fuel because hydrogen releases more energy per unit mass during combustion, enabling a higher exhaust velocity. Hydrocarbon engines are also typically run fuel-rich, which produces some CO instead of CO₂ as a consequence of incomplete combustion.

During engine shutdown, fuel flow goes to zero rapidly, while the engine is still quite hot. Residual and trapped fuel can polymerize or even carbonize at hot spots or in hot components. Even without hot spots, heavy fuels can create a petroleum residue, as can be seen in gasoline, diesel, or jet fuel tanks that have been in service for years.

On the upside, below a chamber pressure of about 1000 psi, kerosene can produce sooty deposits on the inside of the nozzle and chamber liner. This acts as a significant insulation layer, and can reduce the heat flow into the wall by roughly a factor of two.>>

[Chris Peterson]

You need dust, and you need water. Most of the dust in the upper atmosphere comes from meteors, but there are other sources, particularly volcanic eruptions. Where the water comes from is less clear, but one definite source is the vapor from rocket launches. This launch isn't what's seeding the noctilucent clouds- that's still meteoritic dust. The launch is providing the water.

• Are you sure :?: That would seem to be quite inefficient.

Pretty sure. Any I'm not sure what you mean by "inefficient" in this context (nor the relevance of your link to combustion in rocket engines).

[neufer]

You need dust, and you need water. Most of the dust in the upper atmosphere comes from meteors, but there are other sources, particularly volcanic eruptions. Where the water comes from is less clear, but one definite source is the vapor from rocket launches. This launch isn't what's seeding the noctilucent clouds- that's still meteoritic dust. The launch is providing the water.

• Are you sure That would seem to be quite inefficient.

Pretty sure.

Any I'm not sure what you mean by "inefficient" in this context
(nor the relevance of your link to combustion in rocket engines).

• The Falcon 9 second stage is known to produce both water & soot in the same place.
  
  Why would indigenous dust be required?

<<Contrails (short for "condensation trails") are line-shaped clouds sometimes produced by aircraft engine exhaust, typically at aircraft cruise altitudes several miles above the Earth's surface. Contrails are composed primarily of water, in the form of ice crystals. The combination of water vapor in aircraft engine exhaust and the low ambient temperatures that often exist at these high altitudes allows the formation of the trails. Impurities in the engine exhaust from the fuel, including sulfur compounds (0.05% by weight in jet fuel) provide some of the particles that can serve as sites for water droplet growth in the exhaust and, if water droplets form, they might freeze to form ice particles that compose a contrail.>>

[De58te]

Otto Posterman - " noctilucent clouds ... are formed as water vapor in the cold upper atmosphere condenses on meteoric dust or volcanic ash near the edge of space. " If the APOD professors are quite confident there is water vapor in the cold upper atmosphere, why do you doubt their authority?

[MarkBour]

... (On August 28, 2006, scientists with the Mars Express mission announced that they found clouds of carbon dioxide crystals over Mars that extended up to 100 km above the surface of the planet; they are the highest clouds discovered over the surface of a planet.) ...

Interesting. In the referenced article (https://solarsystem.nasa.gov/news/2006/ ... nd-on-mars), it seems that the definition of "visible" was pushed pretty far. It is also interesting that they say "over the surface of a planet". One can immediately consider the gas giants, and they are ruled out of this comparison if we do not know where the surface of the planet is, or if one exists. If we decide that Jupiter or Saturn have something we will agree to call a surface, then ... new record.
It was also instructive (for me) to look at the Wikipedia definition of a cloud:
https://en.wikipedia.org/wiki/Cloud

In meteorology, a cloud is an aerosol comprising a visible mass of minute liquid droplets, frozen crystals, or particles suspended in the atmosphere above the surface of a planetary body. (Primary source, National Weather Service "Weather Terms".)

I'm surprised that this definition is already "solar-system-ready" (and beyond), not simply a definition that is appropriate for Earth. It is a sign of our progress in our experience with atmospheres that we want a definition that is so widely applicable. But this definition means the particles have to be suspended in the planet's atmosphere, so planetary rings and such are not going to qualify.

[Chris Peterson]

• Are you sure :?: That would seem to be quite inefficient.

Pretty sure.

Any I'm not sure what you mean by "inefficient" in this context
(nor the relevance of your link to combustion in rocket engines).

• The Falcon 9 second stage is known to produce both water & soot in the same place.
  
  Why would indigenous dust be required?

It shouldn't be. But dust is ubiquitous in the upper atmosphere. I think the limiting factor is normally the presence of enough water. The rocket launch delivers that. The soot is there, and may be a factor, but it's not the critical component.

[neufer]

• The Falcon 9 second stage is known to produce both water & soot in the same place.
  
  Why would indigenous dust be required?

It shouldn't be. But dust is ubiquitous in the upper atmosphere. I think the limiting factor is normally the presence of enough water. The rocket launch delivers that. The soot is there, and may be a factor, but it's not the critical component.

If dust were truly "ubiquitous" in the upper atmosphere then every hydrogen powered upper stage would produce an impressive noctilucent cloud in the summer. Instead, it has required a kerosene powered upper stage to produce a really impressive summer noctilucent cloud.

[Chris Peterson]

• The Falcon 9 second stage is known to produce both water & soot in the same place.
  
  Why would indigenous dust be required?

It shouldn't be. But dust is ubiquitous in the upper atmosphere. I think the limiting factor is normally the presence of enough water. The rocket launch delivers that. The soot is there, and may be a factor, but it's not the critical component.

If dust were truly "ubiquitous" in the upper atmosphere then every hydrogen powered upper stage would produce an impressive noctilucent cloud in the summer. Instead, it has required a kerosene powered upper stage to produce a really impressive summer noctilucent cloud.

I'd like a larger sample before drawing any conclusions. And while dust and water are definitely required, there may be other factors we're not considering (such as temperature or air motion).