User:Marshallsumter/Radiation astronomy1/Particles

"A skydiver may have captured the first film ever of a meteorite plunging down at terminal velocity, also known as its “dark flight” stage."^[1]

"The footage was captured in 2012 by a helmet cam worn by Anders Helstrup as he and other members of the Oslo Parachute Club jumped from a small plane that took off from an airport in Hedmark, Norway."^[1]

“It can’t be anything else. The shape is typical of meteorites -- a fresh fracture surface on one side, while the other side is rounded.”^[2]

“It has never happened before that a meteorite has been filmed during dark flight; this is the first time in world history.”^[2]

"Having the rock in hand would certainly help. But despite triangulations and analyses, Helstrup and his recruits still haven’t found it."^[1]

Def. a "very small piece of matter, a fragment^[3]; especially, the smallest possible part of something"^[4] is called a particle.

File:Snake Nebula SMA.jpg

Def. the solid material thrown into the air by a volcanic eruption that settles on the surrounding areas is called tephra.

"[T]ephra, is a general term for fragments of volcanic rock and lava that are blasted into the air by volcanic explosions or carried upward in the volcanic plume by hot, hazardous gases. The larger fragments usually fall close to the volcano, but the finer particles can be advected quite some distance. ... [Fine ash] can contain rock, minerals, and volcanic glass fragments smaller than .1 inch in diameter, or slightly larger than the size of a pinhead."^[5]

"[T]he carbonaceous material [is] known from observation to dominate the terrestrial [micrometeorite (MM)] flux."^[6]

"Ureilites occur about half as often as eucrites (Krot et al. 2003), are relatively friable, have less a wide range of cosmic-ray exposure ages including two less than 1 Myr, and, like the dominant group of MM precursors, contain carbon."^[6]

Def. liquid moisture that falls visibly in separate drops is called rain.

The Kerala red rain phenomenon was a blood rain (red rain) event that occurred from July 25 to September 23, 2001, when heavy downpours of red-coloured rain fell sporadically on the southern Indian state of Kerala, staining clothes pink.^[7] Yellow, green, and black rain was also reported.^[8][9][10] Colored rain was also reported in Kerala in 1896 and several times since,^[11] most recently in June 2012.^[12][13]

Red rains were also reported from November 15, 2012 to December 27, 2012 occasionally in eastern and north-central provinces of Sri Lanka,^[14] where scientists from the Sri Lanka Medical Research Institute (MRI) are investigating to ascertain their cause.^[15][16][17]

The colored rain of Kerala began falling on July 25, 2001, in the districts of Kottayam and Idukki in the southern part of the state. Yellow, green, and black rain was also reported.^[8][9][10] Many more occurrences of the red rain were reported over the following ten days, and then with diminishing frequency until late September.^[9]

According to locals, the first colored rain was preceded by a loud thunderclap and flash of light, and followed by groves of trees shedding shriveled grey "burnt" leaves. Shriveled leaves and the disappearance and sudden formation of wells were also reported around the same time in the area.^[18][19][20] It typically fell over small areas, no more than a few square kilometers in size, and was sometimes so localized that normal rain could be falling just a few meters away from the red rain. Red rainfalls typically lasted less than 20 minutes.^[9] Each milliliter of rain water contained about 9 million red particles, and each liter of rainwater contained approximately 100 milligrams of solids. Extrapolating these figures to the total amount of red rain estimated to have fallen, it was estimated that 50,000 kilograms (110,000 lb) of red particles had fallen on Kerala.^[9]

The brownish-red solid separated from the red rain consisted of about 90% round red particles and the balance consisted of debris.^[11] The particles in suspension in the rain water were responsible for the color of the rain, which at times was strongly colored red. A small percentage of particles were white or had light yellow, bluish gray and green tints.^[9] The particles were typically 4 to 10 µm across and spherical or oval. [Transmission electron microscope] Electron microscope images showed the particles as having a depressed center. At still higher magnification some particles showed internal structures.^[9]

In November 2001, commissioned by the Government of India's Department of Science & Technology, the Center for Earth Science Studies (CESS) and the Tropical Botanical Garden and Research Institute (TBGRI) issued a joint report which concluded that:^[11][21]

"The color was found to be due to the presence of a large amount of spores of a lichen-forming alga belonging to the genus Trentepohlia. Field verification showed that the region had plenty of such lichens. Samples of lichen taken from Changanacherry area, when cultured in an algal growth medium, also showed the presence of the same species of algae. Both samples (from rainwater and from trees) produced the same kind of algae, indicating that the spores seen in the rainwater most probably came from local sources."^[21]

Def. a suspension of dry dust in the atmosphere is called a lithometeor.

"A lithometeor consists of solid particles suspended in the air or lifted by the wind from the ground."^[22]

"A lithometeor is the general term for particles suspended in a dry atmosphere; these include dry haze, smoke, dust, and sand."^[5]

"Dry haze is an accumulation of very fine dust or salt particles in the atmosphere; it does not block light, but instead causes light rays to scatter. Dry haze particles produce a bluish color when viewed against a dark background, but look yellowish when viewed against a lighter background. This light-scattering phenomenon (called Mie scattering) also causes the visual ranges within a uniformly dense layer of haze to vary depending on whether the observer is looking into the sun or away from it."^[5]

Heavy metal pollution may occur in lithometeors.^[23]

"The rise of airborne dust is constantly augmenting from the desert (Bilma) to the southern Sahelian stations (Niamey) where it has increased by a factor five. ... the Sahelian zone with airborne dust during the 80s ... All stations have recorded a general increase of wind velocity. The increase of lithometeors frequency as well as the wind velocity during the drought period is not explained by the aridification."^[24]

"The distribution of photographic meteors in iron, stony, and porous meteors is given in this paper".^[25] "[A]mong all the 217 meteors for which we know the beginning there are 70 iron meteors, i. e. about 32 p. c., and 147 stony meteors, i. e. 68 p. c."^[25] The meteor streams: Perseids, Geminids, Taurids, Lyrids, κ Cygnids and Virginids, are quite stony.^[25]

"The dominant group in all cases are stony meteors."^[25]

"The sensors on the IBEX spacecraft are able to detect energetic neutral atoms (ENAs) at a variety of energy levels."^[27]

The satellite's payload consists of two energetic neutral atom (ENA) imagers, IBEX-Hi and IBEX-Lo. Each of these sensors consists of a collimator that limits their fields-of-view, a conversion surface to convert neutral hydrogen and oxygen into ions, an electrostatic analyzer (ESA) to suppress ultraviolet light and to select ions of a specific energy range, and a detector to count particles and identify the type of each ion.

"IBEX–Lo can detect particles with energies ranging from 10 electron–volts to 2,000 electron–volts (0.01 keV to 2 keV) in 8 separate energy bands. IBEX–Hi can detect particles with energies ranging from 300 electron–volts to 6,000 electron–volts (.3 keV to 6 keV) in 6 separate energy bands. ... Looking across the entire sky, interactions occurring at the edge of our Solar System produce ENAs at different energy levels and in different amounts, depending on the process."^[27]

Proton–hydrogen charge-exchange collisions [such as those shown at right] are often the most important process in space plasma because [h]ydrogen is the most abundant constituent of both plasmas and background gases and hydrogen charge-exchange occurs at very high velocities involving little exchange of momentum.

"Energetic neutral atoms (ENA), emitted from the magnetosphere with energies of ∼50 keV, have been measured with solid-state detectors on the IMP 7/8 and ISEE 1 spacecraft. The ENA are produced when singly charged trapped ions collide with the exospheric neutral hydrogen geocorona and the energetic ions are neutralized by charge exchange."^[28]

"The IMAGE mission ... High Energy Neutral Atom imager (HENA) ... images [ENAs] at energies between 10 and 60 keV/nucleon [to] reveal the distribution and the evolution of energetic [ions, including protons] as they are injected into the ring current during geomagnetic storms, drift about the Earth on both open and closed drift paths, and decay through charge exchange to pre‐storm levels."^[29]

"In 2009, NASA's Interstellar Boundary Explorer (IBEX) mission science team constructed the first-ever all-sky map [at right] of the interactions occurring at the edge of the solar system, where the sun's influence diminishes and interacts with the interstellar medium. A 2013 paper provides a new explanation for a giant ribbon of energetic neutral atoms – shown here in light green and blue -- streaming in from that boundary."^[30]

"[T]he boundary at the edge of our heliosphere where material streaming out from the sun interacts with the galactic material ... emits no light and no conventional telescope can see it. However, particles from inside the solar system bounce off this boundary and neutral atoms from that collision stream inward. Those particles can be observed by instruments on NASA’s Interstellar Boundary Explorer (IBEX). Since those atoms act as fingerprints for the boundary from which they came, IBEX can map that boundary in a way never before done. In 2009, IBEX saw something in that map that no one could explain: a vast ribbon dancing across this boundary that produced many more energetic neutral atoms than the surrounding areas."^[30]

""What we are learning with IBEX is that the interaction between the sun's magnetic fields and the galactic magnetic field is much more complicated than we previously thought," says Eric Christian, the mission scientist for IBEX at NASA's Goddard Space Flight Center in Greenbelt, Md. "By modifying an earlier model, this paper provides the best explanation so far for the ribbon IBEX is seeing.""^[30]

At right is the only available X-ray image, by the Chandra X-ray Observatory, of Mira A on the right and Mira B (left). "Mira A is losing gas rapidly from its upper atmosphere [apparently] via a stellar wind. [Mira B is asserted to be a white dwarf. In theory] Mira B exerts a gravitational tug that creates a gaseous bridge between the two stars. Gas from the wind and bridge accumulates in an accretion disk around Mira B and collisions between rapidly moving particles in the disk produce X-rays."^[31]

Mira A, spectral type M7 IIIe^[32], has an effective surface temperature of 2918–3192^[33]. Mira A is not a known X-ray source according to SIMBAD, but here is shown to be one.

"The Boomerang Nebula is a young planetary nebula and the coldest object found in the Universe so far. The NASA/ESA Hubble Space Telescope image is yet another example of how Hubble's sharp eye reveals surprising details in celestial objects."^[34]

"NASA's Hubble Space Telescope caught the Boomerang Nebula [at second right] in images taken with the Advanced Camera for Surveys in early 2005. This reflecting cloud of dust and gas has two nearly symmetric lobes of matter that are being ejected from a central star. Each lobe of the nebula is nearly one light-year in length, making the total length of the nebula half as long as the distance from our Sun to our nearest neighbors- the Alpha Centauri stellar system, located roughly 4 light-years away. The Boomerang Nebula resides 5,000 light-years from Earth. Hubble's sharp view is able to resolve patterns and ripples in the nebula very close to the central star that are not visible from the ground."^[35]

"This NASA/ESA Hubble Space Telescope image [at top right] shows a young planetary nebula known (rather curiously) as the Boomerang Nebula. It is in the constellation of Centaurus, 5000 light-years from Earth. Planetary nebulae form around a bright, central star when it expels gas in the last stages of its life."^[34]

"The Boomerang Nebula is one of the Universe's peculiar places. In 1995, using the 15-metre Swedish ESO Submillimetre Telescope in Chile, astronomers Sahai and Nyman revealed that it is the coldest place in the Universe found so far. With a temperature of -272C, it is only 1 degree warmer than absolute zero (the lowest limit for all temperatures). Even the -270C background glow from the Big Bang is warmer than this nebula. It is the only object found so far that has a temperature lower than the background radiation."^[34]

"The Hubble telescope took this image in 1998. It shows faint arcs and ghostly filaments embedded within the diffuse gas of the nebula's smooth 'bow tie' lobes. The diffuse bow-tie shape of this nebula makes it quite different from other observed planetary nebulae, which normally have lobes that look more like 'bubbles' blown in the gas. However, the Boomerang Nebula is so young that it may not have had time to develop these structures. Why planetary nebulae have so many different shapes is still a mystery."^[34]

"The general bow-tie shape of the Boomerang appears to have been created by a very fierce 500 000 kilometre-per-hour wind blowing ultracold gas away from the dying central star. The star has been losing as much as one-thousandth of a solar mass of material per year for 1500 years. This is 10-100 times more than in other similar objects. The rapid expansion of the nebula has enabled it to become the coldest known region in the Universe."^[34]

"The image was exposed for 1000 seconds through a green-yellow filter. The light in the image comes from starlight from the central star reflected by dust particles."^[34] The image pixels have been coded blue even though the filter is centered at 606 nm.

"The Boomerang nebula, called the "coldest place in the universe," reveals its true shape to the Atacama Large Millimeter/submillimeter Array (ALMA) telescope. The background blue structure, as seen in visible light by NASA's Hubble Space Telescope, shows a classic double-lobe shape with a very narrow central region. ALMA’s resolution and ability to see the cold gas molecules reveals the nebula’s more elongated shape, as seen in red."^[36]

"NGC 3132 [imaged at right] is a striking example of a planetary nebula. This expanding cloud of gas, surrounding a dying star, is known to amateur astronomers in the southern hemisphere as the "Eight-Burst" or the "Southern Ring" Nebula."^[37]

"The name "planetary nebula" refers only to the round shape that many of these objects show when examined through a small visual telescope. In reality, these nebulae have little or nothing to do with planets, but are instead huge shells of gas ejected by stars as they near the ends of their lifetimes. NGC 3132 is nearly half a light year in diameter, and at a distance of about 2000 light years is one of the nearer known planetary nebulae. The gases are expanding away from the central star at a speed of 9 miles per second."^[37]

"This image, captured by NASA's Hubble Space Telescope, clearly shows two stars near the center of the nebula, a bright white one, and an adjacent, fainter companion to its upper right. (A third, unrelated star lies near the edge of the nebula.) The faint partner is actually the star that has ejected the nebula. This star is now smaller than our own Sun, but extremely hot. The flood of ultraviolet radiation from its surface makes the surrounding gases glow through fluorescence. The brighter star is in an earlier stage of stellar evolution, but in the future it will probably eject its own planetary nebula."^[37]

"In the Heritage Team's rendition of the Hubble image, the colors were chosen to represent the temperature of the gases. Blue represents the hottest gas [the oxygen 500.9 nm line], which is confined to the inner region of the nebula. Red represents the coolest gas [hydrogen Hα line], at the outer edge. The Hubble image also reveals a host of filaments, including one long one that resembles a waistband, made out of dust particles which have condensed out of the expanding gases. The dust particles are rich in elements such as carbon. Eons from now, these particles may be incorporated into new stars and planets when they form from interstellar gas and dust. Our own Sun may eject a similar planetary nebula some 6 billion years from now."^[37]

The yellow line, or band, used as an intermediate temperature is due to the overlap between the oxygen cyan line and the Hα line.

"[T]he extended red emission (ERE) [is] observed in many dusty astronomical environments, in particular, the diffuse interstellar medium of the Galaxy. ... silicon nanoparticles provide the best match to the spectrum and the efficiency requirement of the ERE."^[38]

"The ERE was first recognized clearly in the peculiar reflection nebula called the Red Rectangle by Schmidt, Cohen, & Margon (1980)."^[38]

The Red Rectangle Nebula, so called because of its red color and unique rectangular shape, is a protoplanetary nebula in the Monoceros constellation. Also known as HD 44179, the nebula was discovered in 1973 during a rocket flight associated with the AFCRL Infrared Sky Survey called Hi Star.

The "ERE manifests itself through a broad, featureless emission band of 60 < FWHM < 100 nm, with a peak appearing in the general wavelength range 610 < λ_p < 820 nm."^[38]

In the Red Rectangle Nebula, diffraction-limited speckle images of it in visible and near infrared light reveal a highly symmetric, compact bipolar nebula with X-shaped spikes which imply toroidal dispersion of the circumstellar material. The central binary system is completely obscured, providing no direct light.^[39]

"The star HD 44179 is surrounded by an extraordinary structure known as the Red Rectangle. It acquired its moniker because of its shape and its apparent colour when seen in early images from Earth. This strikingly detailed new Hubble image reveals how, when seen from space, the nebula, rather than being rectangular, is shaped like an X with additional complex structures of spaced lines of glowing gas, a little like the rungs of a ladder. The star at the centre is similar to the Sun, but at the end of its lifetime, pumping out gas and other material to make the nebula, and giving it the distinctive shape. It also appears that the star is a close binary that is surrounded by a dense torus of dust — both of which may help to explain the very curious shape. Precisely how the central engine of this remarkable and unique object spun the gossamer threads of nebulosity remains mysterious. It is likely that precessing jets of material played a role."^[40]

"The Red Rectangle is an unusual example of what is known as a proto-planetary nebula. These are old stars, on their way to becoming planetary nebulae. Once the expulsion of mass is complete a very hot white dwarf star will remain and its brilliant ultraviolet radiation will cause the surrounding gas to glow. The Red Rectangle is found about 2 300 light-years away in the constellation Monoceros (the Unicorn)."^[40]

"The High Resolution Channel of the NASA/ESA Hubble Space Telescope’s Advanced Camera for Surveys captured this view of HD 44179 and the surrounding Red Rectangle nebula — the sharpest view so far. Red light from glowing Hydrogen was captured through the F658N filter and coloured red. Orange-red light over a wider range of wavelengths through a F625W filter was coloured blue."^[40]

"NASA's new Spitzer Space Telescope has captured [the image right] of an unusual comet that experiences frequent outbursts, which produce abrupt changes in brightness. Periodic comet Schwassmann-Wachmann I (P/SW-1) has a nearly circular orbit just outside that of Jupiter, with an orbital period of 14.9 years. It is thought that the outbursts arise from the build-up of internal gas pressure as the heat of the Sun slowly evaporates frozen carbon dioxide and carbon monoxide beneath the blackened crust of the comet nucleus. When the internal pressure exceeds the strength of the overlying crust, a rupture occurs, and a burst of gas and dust fragments is ejected into space at speeds of 450 miles per hour (200 meters per second)."^[41]

"This 24-micron image of P/SW-1 was obtained with Spitzer's multiband imaging photometer. The image shows thermal infrared emission from the dusty coma and tail of the comet. The nucleus of the comet is about 18 miles (30 kilometers) in diameter and is too small to be resolved by Spitzer. The micron-sized dust grains in the coma and tail stream out away from the Sun. The dust and gas comprising the comet's nucleus is part of the same primordial materials from which the Sun and planets were formed billions of years ago. The complex carbon-rich molecules they contain may have provided some of the raw materials from which life originated on Earth."^[41]

"Schwassmann-Wachmann 1 is thought to be a member of a relatively new class of objects called "Centaurs," of which 45 objects are known. These are small icy bodies with orbits between those of Jupiter and Neptune. Astronomers believe that Centaurs are recent escapees from the Kuiper Belt, a zone of small bodies orbiting in a cloud at the distant reaches of the solar system."^[41]

"Two asteroids, 1996 GM36 (left) and 5238 Naozane (right) were serendipitously captured in the comet image. Because they are closer to us than the comet and have faster orbital velocities, they appear to move relative to the comet and background stars, thereby producing a slight elongated appearance. The Spitzer data have allowed astronomers to use thermal measurements, which reduce the uncertainties of visible-light albedo (reflectivity) measurements, to determine their size. With radii of 1.4 and 3.0 kilometers, these are the smallest main-belt asteroids yet measured by infrared means."^[41]

In the second image pair, "NASA's Spitzer Space Telescope captured the picture on the left of comet Holmes in March 2008, five months after the comet suddenly erupted and brightened a millionfold overnight. The contrast of the picture has been enhanced on the right to show the anatomy of the comet."^[42]

"Every six years, comet 17P/Holmes speeds away from Jupiter and heads inward toward the sun, traveling the same route typically without incident. However, twice in the last 116 years, in November 1892 and October 2007, comet Holmes mysteriously exploded as it approached the asteroid belt. Astronomers still do not know the cause of these eruptions."^[42]

"Spitzer's infrared picture at left reveals fine dust particles that make up the outer shell, or coma, of the comet. The nucleus of the comet is within the bright whitish spot in the center, while the yellow area shows solid particles that were blown from the comet in the explosion. The comet is headed away from the sun, which lies beyond the right-hand side of the picture."^[42]

"The contrast-enhanced picture on the right shows the comet's outer shell, and strange filaments, or streamers, of dust. The streamers and shell are a yet another mystery surrounding comet Holmes. Scientists had initially suspected that the streamers were small dust particles ejected from fragments of the nucleus, or from hyperactive jets on the nucleus, during the October 2007 explosion. If so, both the streamers and the shell should have shifted their orientation as the comet followed its orbit around the sun. Radiation pressure from the sun should have swept the material back and away from it. But pictures of comet Holmes taken by Spitzer over time show the streamers and shell in the same configuration, and not pointing away from the sun. The observations have left astronomers stumped."^[42]

"The horizontal line seen in the contrast-enhanced picture is a trail of debris that travels along with the comet in its orbit."^[42]

"The Spitzer picture was taken with the spacecraft's multiband imaging photometer at an infrared wavelength of 24 microns."^[42]

"The deuterium enrichment of cometary water is one of the most important cosmogonic indicators in comets. The (D/H)_H2O ratio preserves information about the conditions under which comet material formed, and tests the possible contribution of comets in delivering water for Earth's oceans. Water (H₂O) and HDO were sampled in comet 8P/Tuttle from 2008 January 27 to 2008 February 3 using the new IR spectrometer (Cryogenic Infrared Echelle Spectrograph) at the 8.2 m Antu telescope of the Very Large Telescope Observatory atop Cerro Paranal, Chile."^[43]

File:1989-11-06 Okazaki 19891106 mpm.jpg

"Comet [Okazaki-Levy-Rudenko] was [observed November 18-20 and 22-24, 1989 UTC and] found to be a weak but persistent source at 800 μm".^[44]

"The submillimeter emission from [a cometary] nucleus can be estimated under the assumption of thermal equilibrium."^[44]

"[V]isible meteors consist of 0.1- to 1-mm-sized debris from active comets (Williams 1990)."^[44]

The "effective opacity decreases as a+ [the maximum grain radius] increases in [the] radius range [1 to 100 mm], apparently because the larger particles become individually optically thick and so contribute to the mass [the total grain mass of the cometary coma] faster than they contribute to the radiating cross section."^[44]

"Calculations were made using the wavelength-dependent complex refractive indices of silicate (Draine 1985), glassy carbon (Edoh 1983), and Tholin (Khare et al. 1984). [...] these materials were chosen as broadly representative of the types of matter thought to be present in comet dust."^[44]

"Comet [Okazaki-Levy-Rudenko] was [observed November 18-20 and 22-24, 1989 UTC and] found to be a weak but persistent source at 800 μm".^[44]

Def. "nonsorted, noncalcareous terrigenous deposits composed of sand and/or larger particles dispersed through a muddy matrix"^[45] are called diamictons.

Def. a lithified diamicton is called a diamictite.^[45]

"Such rocks have in common a mixed, ill-sorted, disperse-megaclastic lithology with a great to extreme range of size grades."^[45] The definitions of these rocks are "without regard to origin".^[45]

Def. a " sedimentary, calcareous conglomerate containing a mixture of particles; mixtite"^[46] is called a diamictite.

Def. a rock "of felsic composition, with aphanitic to porphyritic texture"^[47] is called a rhyolite.

"Rhyolite is a light-colored rock with silica (SiO₂) content greater than about 68 weight percent. Sodium and potassium oxides both can reach about 5 weight percent. Common mineral types include quartz, feldspar and biotite and are often found in a glassy matrix. Rhyolite is erupted at temperatures of 700 to 850° C."^[48]

"Rhyolite can look very different, depending on how it erupts. Explosive eruptions of rhyolite create pumice, which is white and full of bubbles. Effusive eruptions of rhyolite often produce obsidian, which is bubble-free and black."^[48]

"Some of the United States' largest and most active calderas formed during eruption of rhyolitic magmas (for example, Yellowstone in Wyoming, Long Valley in California and Valles in New Mexico)."^[48]

"Rhyolite often erupts explosively because its high silica content results in extremely high viscosity (resistance to flow), which hinders degassing. When bubbles form, they can cause the magma to explode, fragmenting the rock into pumice and tiny particles of volcanic ash."^[48]

A dust devil is a strong, well-formed, and relatively long-lived whirlwind, ranging from small (half a metre wide and a few metres tall) to large (more than 10 metres wide and more than 1000 metres tall). The primary vertical motion is upward. Dust devils are usually harmless, but can on rare occasions grow large enough to pose a threat to both people and property.^[49]

Dust devils form when a pocket of hot air near the surface rises quickly through cooler air above it, forming an updraft. If conditions are just right, the updraft may begin to rotate. As the air rapidly rises, the column of hot air is stretched vertically, thereby moving mass closer to the axis of rotation, which causes intensification of the spinning effect by conservation of angular momentum. The secondary flow in the dust devil causes other hot air to speed horizontally inward to the bottom of the newly forming vortex. As more hot air rushes in toward the developing vortex to replace the air that is rising, the spinning effect becomes further intensified and self-sustaining. A dust devil, fully formed, is a funnel-like chimney through which hot air moves, both upwards and in a circle. As the hot air rises, it cools, loses its buoyancy and eventually ceases to rise. As it rises, it displaces air which descends outside the core of the vortex. This cool air returning acts as a balance against the spinning hot-air outer wall and keeps the system stable.^[50]

As available hot air near the surface is channeled up the dust devil, eventually surrounding cooler air will be sucked in. Once this occurs, the effect is dramatic, and the dust devil dissipates in seconds. Usually this occurs when the dust devil is not moving fast enough (depletion) or begins to enter a terrain where the surface temperatures are cooler.^[51]

On rare occasions, a dust devil can grow very large and intense, sometimes reaching a diameter of up to 300 feet (90 m) with winds in excess of 60 mph (100 km/h+) and can last for upwards of 20 minutes before dissipating.^[52]

Dust devils typically do not cause injuries, but rare, severe dust devils have caused damage and even deaths in the past. One such dust devil struck the Coconino County, Arizona, Fairgrounds in Flagstaff, Arizona, on September 14, 2000, causing extensive damage to several temporary tents, stands and booths well as some permanent fairgrounds structures. Several injuries were reported, but there were no fatalities. Based on the degree of damage left behind, it is estimated that the dust devil produced winds as high as 75 mph (120 km/h), which is equivalent to an Enhanced Fujita Scale (EF-0) tornado.^[53] On May 19, 2003, a dust devil lifted the roof off a two-story building in Lebanon, Maine, causing it to collapse and kill a man inside.^[54][55] In East El Paso, Texas in 2010, three children in an inflatable jump house were picked up by a dust devil and lifted over 10 feet (3 m), traveling over a fence and landing in a backyard three houses away.^[56] In Commerce City, Colorado in 2018, a powerful dust devil hurtled two porta-potties into the air. No one was injured in the incident.^[57] In 2019 a large dust devil in Yucheng county, Henan province, China killed 2 children and injured 18 children and 2 adults when a bouncy castle was lifted into the air.^[58]

Dust devils have been implicated in around 100 aircraft accidents.^[59] While many incidents have been simple taxiing problems, a few have had fatal consequences. Dust devils are also considered major hazards among skydivers and paragliding pilots as they can cause a parachute or a glider to collapse with little to no warning, at altitudes considered too low to cut away, and contribute to the serious injury or death of parachutists.^[60][61][62]

Dust devils, even small ones (on Earth), can produce radio noise and electrical fields greater than 10,000 volts per meter.^[63] A dust devil picks up small dirt and dust particles. As the particles whirl around, they bump and scrape into each other and become electrically charged. The whirling charged particles also create a magnetic field that fluctuates between 3 and 30 times each second.^[64]

A large dust devil measuring about 100 metres (330 ft) across at its base can lift about 15 metric tonnes (17 short tons) of dust into the air in 30 minutes. Giant dust storms that sweep across the world's deserts contribute 8% of the mineral dust in the atmosphere each year during the handful of storms that occur. In comparison, the significantly smaller dust devils that twist across the deserts during the summer lift about three times as much dust, thus having a greater combined impact on the dust content of the atmosphere. When this occurs, they are often called sand pillars.^[65]

Def. "very high-altitude^[66] [shining or glowing at night;^[67] nightshining^[68]] clouds that reflect sunlight long after sunset"^[69] are called noctilucent clouds.

Noctilucent clouds may occasionally take on more of a red or orange hue.^[70]

They are not common or widespread enough to have a significant effect on climate.^[71]

An increasing frequency of occurrence of noctilucent clouds since the 19th century may be the result of climate change.^[72]

Noctilucent clouds are the highest in the atmosphere and form near the top of the mesosphere at about ten times the altitude of tropospheric high clouds.^[73]

Convective lift in the mesosphere is strong enough during the polar summer to cause adiabatic cooling of small amount of water vapour to the point of saturation which tends to produce the coldest temperatures in the entire atmosphere just below the mesopause resulting in the best environment for the formation of polar mesospheric clouds.^[71]

Smoke particles from burnt-up meteors provide much of the condensation nuclei required for the formation of noctilucent cloud.^[74]

Sightings are rare more than 45 degrees south of the north pole or north of the south pole.^[70]

"The mesopause occurs, by definition, at the top of the mesosphere and at the bottom of the thermosphere. Noctilucent clouds appear always in the vicinity of the mesopause."^[75]

From 1972 to 1975 NASA launched the AEROS and AEROS B satellites to study the F region.^[76] "The Es layer (sporadic E-layer) is characterized by small, thin clouds of intense ionization, which can support reflection of radio waves, rarely up to 225 MHz."^[77]

"The total time for transport of metal ions from the equatorial E region to the higher latitudes (within ± 30" magnetic latitude) of the F region must not exceed about 12 hours if the entire "circulation" process is to occur during the time the fountain effect is operative. This requirement seems unnecessary in that the "reverse fountain effect" which occurs when the daytime eastward E field reverses to the west is weaker than the daytime fountain (WOODMAN et al., 1977) thus leading to an apparent daily net positive flux of metal ions into the equatorial F region from the equatorial E region. Some evidence for this "pulsed" source of metal ions is found in the observed "clouds" of Mg⁺ reported by MENDE et al., (1985) and possibly by KUMAR and HANSON (1980)."^[78]

During solar proton events, ionization can reach unusually high levels in the D-region over high and polar latitudes, known as Polar Cap Absorption (or PCA) events, because the increased ionization significantly enhances the absorption of radio signals passing through the region.^[79]

"Dust quite probably plsys a major role in noctilucent cloud formation (TURCO et al., 1982) and possibly modifies D region ion chemistry (eg. PARTHASARATHY, 1976)."^[78]

"Dust has long been considered important to the formation of noctiluent clouds at high latitudes. TURCO et al., (1982) extensively treats the problem of noctilucent cloud formation including effects of ion attachment to dust or ice particles. PARTHASARATHY (1976) has considered dust a direct "sink" for D region ionization."^[78]

"[N]octilucent clouds are not an aspect of low and mid-laditude D region aeronomy."^[78]

The Quadrantids (QUA) are a January meteor shower, with the zenithal hourly rate (ZHR) of this shower as high as that of two other reliably rich meteor showers, the Perseids in August and the Geminids in December.^[80]

The meteor rates exceed one-half of their highest value for only about eight hours (compared to two days for the August Perseids), which means that the stream of particles that produces this shower is narrow, and apparently deriving within the last 500 years from some orbiting body.^[81] The parent body of the Quadrantids was tentatively identified in 2003^[82] as the minor planet (196256) 2003 EH1, which in turn may be related to the comet C/1490 Y1^[83] that was observed by Chinese, Japanese and Korean astronomers some 500 years ago.

File:162173 Ryugu.jpg

Note that sizes and distances of bodies and orbits are not to scale in the image on the right.

As of 2015, the Apollo asteroid group includes a total of 6,923 known objects of which 991 are numbered (JPL SBDB).

Ryugu shown on the left was discovered on 10 May 1999 by astronomers with the Lincoln Near-Earth Asteroid Research at the Lincoln Laboratory's Experimental Test Site near Socorro, New Mexico, in the United States.^[84]

The asteroid was officially named "Ryugu" by the Minor Planet Center on 28 September 2015.^[85]

Initial images taken by the Hayabusa-2 spacecraft on approach at a distance of 700 km were released on 14 June 2018 and revealed a diamond shaped body and confirmed its retrograde rotation.^[86]

Between 17 and 18 June 2018, Hayabusa 2 went from 330 km to 240 km from Ryugu and captured a series of additional images from the closer approach.^[87]

On 21 September 2018, the first two of these rovers, which will hop around the surface of the asteroid, were released from Hayabusa2.^[88]

On September 22, 2018, JAXA confirmed the two rovers had successfully touched down on Ryugu's surface which marks the first time a mission has completed a successful landing on a fast-moving asteroid body.^[89]

"This series of images [second down on the right] taken by the OSIRIS-REx spacecraft shows Bennu in one full rotation from a distance of around 50 miles (80 km). The spacecraft’s PolyCam camera obtained the 36 2.2-millisecond frames over a period of four hours and 18 minutes."^[90]

101955 Bennu (provisional designation 1999 RQ₃₆^[91], a C-type carbonaceous asteroid in the Apollo group discovered by the Lincoln Near-Earth Asteroid Research (LINEAR) Project on September 11, 1999, is a potentially hazardous object that is listed on the Sentry monitoring system, Sentry Risk Table, with the second-highest cumulative rating on the Palermo Technical Impact Hazard Scale.^[92] It has a cumulative 1-in-2,700 chance of impacting Earth between 2175 and 2199.^[93][94]

101955 Bennu has a mean diameter of approximately 492 m (1,614 ft; 0.306 mi) and has been observed extensively with the Arecibo Observatory planetary radar and the Goldstone Deep Space Communications Complex NASA Deep Space Network.^[95][96][97]

Asteroid Bennu has a roughly spheroidal shape, resembling a spinning top, with the direction of rotation about its axis retrograde with respect to its orbit and a fairly smooth shape with one prominent 10–20 m boulder on its surface, in the southern hemisphere.^[94]

There is a well-defined ridge along the equator of asteroid Bennu that suggests that fine-grained regolith particles have accumulated in this area, possibly because of its low gravity and fast rotation.^[94]

Observations of this minor planet by the Spitzer Space Telescope in 2007 gave an effective diameter of 484±10 m, which is in line with other studies. It has a low visible geometric albedo of 0.046±0.005. The thermal inertia was measured and found to vary by ±19% during each rotational period suggesting that the regolith grain size is moderate, ranging from several millimeters up to a centimeter, and evenly distributed. No emission from a potential dust coma has been detected around asteroid Bennu, which puts a limit of 10⁶ g of dust within a radius of 4750 km.^[98]

Astrometric observations between 1999 and 2013 have demonstrated that 101955 Bennu is influenced by the Yarkovsky effect, causing the semimajor axis to drift on average by 284±1.5 meters/year; analysis of the gravitational and thermal effects give a bulk density of ρ = 1260±70 kg/m³, which is only slightly denser than water, the predicted macroporosity is 40±10%, suggesting that the interior has a rubble pile structure, with an estimated mass is 7.8±0.9×10¹⁰
 kg.^[99]

Photometric observations of Bennu in 2005 yielded a synodic rotation period of 4.2905±0.0065 h, a B-type asteroid classification, which is a sub-category of C-type asteroid or carbonaceous asteroids. Polarimetric observations show that Bennu belongs to the rare F-type asteroid or F subclass of carbonaceous asteroids, which is usually associated with cometary features.^[100] Measurements over a range of phase angles show a phase function slope of 0.040 magnitudes per degree, which is similar to other near-Earth asteroids with low albedo.^[101]

Asteroid Bennu's basic mineralogy and chemical nature would have been established during the first 10 million years of the Solar System's formation, where the carbonaceous material underwent some geologic heating and chemical transformation into more complex minerals.^[94] Bennu probably began in the inner asteroid belt as a fragment from a larger body with a diameter of 100 km, where simulations suggest a 70% chance it came from the Polana family and a 30% chance it derived from the 495 Eulalia (Eulalia family).^[102]

Subsequently, the orbit drifted as a result of the Yarkovsky effect and mean motion resonances with the giant planets, such as Jupiter and Saturn modified the asteroid, possibly changing its spin, shape, and surface features.^[103]

A possible cometary origin for Bennu, based on similarities of its spectroscopic properties with known comets, with the estimated fraction of comets in the population of Near Earth asteroids is 8±5 %.^[100]

Def. a "region of the orbital plane of the solar system located between the orbits of Mars and Jupiter which is occupied by numerous minor planets and the dwarf planet Ceres"^[104] is called an asteroid belt.

"The MB group is the most numerous group of MCs. ... 50 % of the MB Mars-crossers [MCs] become ECs within 59.9 Myr and [this] contribution ... dominates the production of ECs".^[105] MB denotes the main belt of asteroids.^[105]

The interplanetary medium includes interplanetary dust, cosmic rays and hot plasma from the solar wind. The temperature of the interplanetary medium varies. For dust particles within the asteroid belt, typical temperatures range from 200 K (−73 °C) at 2.2 AU down to 165 K (−108 °C) at 3.2 AU^[106] The density of the interplanetary medium is very low, about 5 particles per cubic centimeter in the vicinity of the Earth; it decreases with increasing distance from the sun, in inverse proportion to the square of the distance. It is variable, and may be affected by magnetic fields and events such as coronal mass ejections. It may rise to as high as 100 particles/cm³.

"The hydromagnetic approach led to the discovery of two important observational regularities in the solar system: (1) the band structure [such as in the rings of Saturn and in the asteroid belt], and (2) the cosmogonic shadow effect (the two-thirds fall down effect)."^[107]

The majority of known asteroids orbit within the asteroid belt between the orbits of Mars and Jupiter ... This belt is now estimated to contain between 1.1 and 1.9 million asteroids larger than 1 km in diameter,^[108] and millions of smaller ones.^[109]

At second right is an approximately natural color image of the asteroid 243 Ida. "There are brighter areas, appearing bluish in the picture, around craters on the upper left end of Ida, around the small bright crater near the center of the asteroid, and near the upper right-hand edge (the limb). This is a combination of more reflected blue light and greater absorption of near infrared light, suggesting a difference in the abundance or composition of iron-bearing minerals in these areas."^[110]

"The [Sloan Digital Sky Survey] SDSS “blue” asteroids are related to the C-type (carbonaceous) asteroids, but not all of them are C-type. They are a mixture of C-, E-, M-, and P-types."^[111]

The possible importance of the Yarkovsky effect is the movement of meteoroids about the Solar System.^[112]

The diurnal effect is the dominant component for bodies with diameter greater than about 100 m.^[113]

On very long timescales over which the spin axis of the body may be repeatedly changed due to collisions (and hence also the direction of the diurnal effect changes), the seasonal effect will also tend to dominate.^[113]

The effect was first measured in 1991–2003 on the asteroid 6489 Golevka which drifted 15 km from its predicted position over twelve years (the orbit was established with great precision by a series of radar observations in 1991, 1995 and 1999 from the Arecibo Observatory radio telescope).^[114]

The "population of asteroids in comet-like orbits using available asteroid size and albedo catalogs of data taken with the Infrared Astronomical Satellite [I], AKARI [A], and the Wide-field Infrared Survey Explorer [W] on the basis of their orbital properties (i.e., the Tisserand parameter with respect to Jupiter, T_J, and the aphelion distance, Q, [is] 123 asteroids in comet-like orbits [with] Q < 4.5 AU and T_J < 3, [including] a considerable number (i.e., 25 by our criteria) of asteroids in comet-like orbits have high albedo, pv > 0.1. [As] such high-albedo objects mostly consist of small (D < 3 km) bodies distributed in near-Earth space (with perihelion distance of q < 1.3 AU) [may be] susceptible to the Yarkovsky effect and drifted into comet-like orbits via chaotic resonances with planets."^[115]

"There are 138,285 asteroids whose albedos and sizes are given in the I–A–W catalog. [...] nearly all high-albedo [asteroids in comet-like orbits] ACOs consist of small asteroids at q < 1.3 AU. This trend cannot be explained by the observational bias. Because the result is obtained based on the mid-infrared data, which, unlike optical observations, are less sensitive to albedo values, it provides reliable sets of asteroid albedo information. If there are big ACOs with high albedo beyond q = 1.3 AU, they would be detected easily. Although further dynamical study is essential to evaluate the population quantitatively, we propose that such ACOs with high albedos were injected from the domain of T_J > 3 via the Yarkovsky effect, because small objects with higher surface temperature are susceptible to the thermal drag force and gradually change their orbital elements to be observed as ACOs in our list."^[115]

"Although there are uncertainties in the dynamical simulation such as the value of the Yarkovsky force and the rocket force (for active comets), we conservatively consider that these three objects (2000 SU236, 2008 UM7, and 2009 SC298) are ACOs and PDCs. ["potential dormant comet" (PDC) is one having a low albedo (pv < 0.1) among ACOs. The second term is a paronomasia associating the spectra of potential dormant comets with spectra similar to P-type, D-type, or C-type asteroids (Licandro et al. 2008; DeMeo & Binzel 2008).]"^[115]

"Let us consider how the Yarkovsky effect moves an asteroid into a comet-like orbit. As shown [...], high-albedo ACOs concentrate in a range of 2 < a < 3.5 AU, similar to main-belt asteroids and [Jupiter-family comets] JFCs. The Tisserand parameter is a function of a, e, and i, [the semimajor axis, eccentricity, and inclination, respectively] while the Yarkovsky effect changes a. Due to the similarity in a between high-albedo ACOs and main-belt asteroids, we conjecture that subsequent dynamical effects may change e and i. Widely known as a standard model for orbital evolution of near-Earth asteroids, the Yarkovsky effect could move small main-belt asteroids' orbits until they are close to resonances with planets, and subsequently, these resonances can push them into terrestrial planet crossing orbits (see, e.g., Morbidelli et al. 2002). Numerical simulations demonstrated that chaotic resonances cause a significant increase in the e and i of test particles in the resonance regions (Gladman et al. 1997). Bottke et al. (2002) suggested that some objects on T_J < 3 (or even T_J < 2) can result from chaotic resonances. [...] Although there are a couple of ACOs close to resonances, their semimajor axes are not related to these major resonances. Therefore, it may be reasonable to think that encounters with terrestrial planets as well as chaotic resonances with massive planets can drift main-belt asteroids into comet-like orbits."^[115]

"In particular, we stress again the significance of high-albedo ACOs. As we discussed through our ground-based observation with the Subaru Telescope, high-albedo ACOs, which may have composition similar to silicaceous asteroids, definitively exist in the I–A–W database. Considering the very low T_J as well as the small size and perihelion distance, we suggest that such high-albedo ACOs have been injected via nongravitational forces, most likely the Yarkovsky effect."^[115]

The submillimeter "wavelength view [at right] of a ring of dust particles around Epsilon Eridani, taken with the SCUBA camera at the James Clerk Maxwell Telescope. The false-colour scale is brightest where there is more dust. Epsilon Eridani is marked by the star symbol, although the star itself is not seen at submillimetre wavelengths. Pluto's orbit (marking the edge of our Solar System) is shown at the same scale."^[116]

"The ring is "strikingly similar" to the outer comet zone in our Solar System, and shows an intriguing bright region that may be particles trapped around a young planet."^[116]

"What we see looks just like the comet belt on the outskirts of our Solar System, only younger, [...] It's the first time we've seen anything like this around a star similar to our Sun. In addition, we were amazed to see a bright spot in the ring, which may be dust trapped in orbit around a planet."^[116]

"Epsilon Eridani is far more similar to our Sun than either Vega or Fomalhaut."^[116]

"This star system is a strong candidate for planets, but if there are planets, it's unlikely there could be life yet. When the Earth was this young, it was still being very heavily bombarded by comets and other debris."^[116]

"It is also a star in our local neighbourhood, being only about 10 light years away, which is why we can see so much detail in the new image."^[116]

"If an astronomer could have seen what our Solar System looked like four billion years ago, it would have been very much as Epsilon Eridani looks today, [...] This is a star system very like our own, and the first time anyone has found something that truly resembles our Solar System; it's one thing to suspect that it exists, but another to actually see it, and this is the first observational evidence."^[117]

"Beyond Pluto in our Solar System is a region containing more than 70,000 large comets, and hundreds of millions of smaller ones, called the "Kuiper belt". The image [...] shows dust particles that the astronomers believe are analogous to our Kuiper belt at the same distance from Epsilon Eridani as the Kuiper belt is from our Sun. Although the image cannot reveal comets directly, the dust that is revealed is believed to be debris from comets."^[116]

"Epsilon Eridani's inner region contains about 1,000 times more dust than our Solar System's inner region, which may mean it has about 1,000 times more comets [...]. Epsilon Eridani is believed to be only 500 million years to 1 billion years old; our Sun is estimated to be 4.5 billion years old, and its inner region is believed to have looked very similar at that age."^[116]

"The new image -- which is from short-radio wavelengths, and is not an optical picture -- was obtained using the 15-meter James Clerk Maxwell Telescope [JCMT] at the Mauna Kea Observatory in Hilo, Hawaii. The JCMT is the world's largest telescope dedicated to the study of light at "submillimeter" wavelengths. The [...] camera called SCUBA (Submillimeter Common User Bolometer Array), which was built by the Royal Observatory in Edinburgh (which is now the UK Astronomical Technology Centre). SCUBA uses detectors cooled to a tenth of a degree above absolute zero (-273 degrees Celsius) to measure the tiny amounts of heat emission from small dust particles at a wavelength close to one-millimeter."^[116]

"The implication is that if there is one system similar to ours at such a close star, presumably there are many others, [...] In the search for life elsewhere in the universe, we have never known where to look before. Now, we are closing in on the right candidates in the search for life."^[117]

"A region near the star that is partially evacuated indicates that planets may have formed, [...] the presence of planets is the most likely explanation for the absence of dust in this region because planets absorb the dust when they form."^[116]

"There may be a planet stirring up the dust in the ring and causing the bright spot, or it could be the remnants of a massive collision between comets."^[118]

The planetary system of KIC 12557548 consists of one extrasolar planet, named Kepler-1520 b which appears to possess a tail of dust and gas formed in a similar fashion to that of a comet^[119] but, as opposed to the tail of a comet, it contains molecules of pyroxene and aluminium(III) oxide. Based on the rate at which the particles in the tail are emitted, the mass of the planet has been constrained to less than 0.02 Earth masses — a higher-mass planet would have too much gravity to sustain the observed rate of mass loss.^[120][121]

Kepler-1520 is at J2000 19^h 23^m 51.8899^s[122] +51° 30′ 16.98″^[122] in the constellation Cygnus, with an apparent magnitude in the visible of 16.7,^[121] spectral class K4V^[123] details

1. mass = 0.76 ± 0.03^[124]
2. radius = 0.71 ± 0.026^[124]
3. luminosity = 0.14^[121]
4. surface gravity (log g) = 4.610 +0.018 or −0.031 cgs^[124]
5. temperature = 4677 +82 or -71^[124]
6. metallicity/Fe = 0.04 ± 0.15^[124]
7. rotation = 22.91±0.24 days^[125]
8. age in gyr = 4.47^[124]

The star is particularly important, as measurements taken by the Kepler spacecraft indicate that the variations in the star's light curve cover a range from about 0.2% to 1.3% of the star's light being blocked.^[121] This indicates that there may be a rapidly disintegrating planet, a prediction not yet conclusively confirmed, in orbit around the star, losing mass at a rate of 1 Earth mass every billion years.^[121] The planet itself is about 0.1 Earth masses,^[126] or just twice the mass of Mercury, and is expected to disintegrate in about 100^[126]-200 million years.^[121] The planet orbits its star in just 15.7 hours,^[121] at a distance only two stellar diameters away from the star's surface,^[119] and has an estimated effective temperature of about 2255 K.^[126] The orbital period of the planet is one of the shortest ever detected in the history of the extrasolar planet search.^[127] In 2016, the planet was confirmed as part of a data release by the Kepler spacecraft.

Geminga may be a sort of neutron star: the decaying core of a massive star that exploded as a supernova about 300,000 years ago.^[128]

"Geminga is a very weak neutron star and the pulsar next to us, which almost only emits extremely hard gamma-rays, but no radio waves. ... Some thousand years ago our Sun entered this [Local Bubble] several hundred light-years big area, which is nearly dust-free."^[129]

The nature of Geminga was quite unknown for 20 years after its discovery by NASA's Second Small Astronomy Satellite (SAS-2). In March 1991 the ROSAT satellite detected a periodicity of 0.237 seconds in soft x-ray emission. This nearby explosion may be responsible for the low density of the interstellar medium in the immediate vicinity of the Solar System. This low-density area is known as the Local Bubble.^[130] Possible evidence for this includes findings by the Arecibo Observatory that local micrometre-sized interstellar meteor particles appear to originate from its direction.^[131] Geminga is the first example of a radio-quiet pulsar, and serves as an illustration of the difficulty of associating gamma-ray emission with objects known at other wavelengths: either no credible object is detected in the error region of the gamma-ray source, or a number are present and some characteristic of the gamma-ray source, such as periodicity or variability, must be identified in one of the prospective candidates (or vice-versa as in the case of Geminga).

Def. a "large and relatively dense cloud of cold gas and dust in interstellar space from which new stars are formed"^[132] is called a molecular cloud.

The image on the right is a composite of visible (B 440 nm and V 557 nm) and near-infrared (768 nm) of the dark cloud (absorption cloud) Barnard 68.^[133]

Barnard 68 is around 500 lyrs away in the constellation Ophiuchus.^[133]

"At these wavelengths, the small cloud is completely opaque because of the obscuring effect of dust particles in its interior."^[133]

"It was obtained with the 8.2-m VLT ANTU telescope and the multimode FORS1 instrument in March 1999."^[133]

A vast assemblage of molecular gas with a mass of approximately 10³–10⁷ times the mass of the Sun^[134] is called a giant molecular cloud (GMC). GMCs are ≈15–600 light-years in diameter (5–200 parsecs).^[134] Whereas the average density in the solar vicinity is one particle per cubic centimetre, the average density of a GMC is 10²–10³ particles per cubic centimetre. Although the Sun is much denser than a GMC, the volume of a GMC is so great that it contains much more mass than the Sun. The substructure of a GMC is a complex pattern of filaments, sheets, bubbles, and irregular clumps.^[135]

The densest parts of the filaments and clumps are called "molecular cores", whilst the densest molecular cores are, unsurprisingly, called "dense molecular cores" and have densities in excess of 10⁴–10⁶ particles per cubic centimeter. Observationally molecular cores are traced with carbon monoxide and dense cores are traced with ammonia. The concentration of dust within molecular cores is normally sufficient to block light from background stars so that they appear in silhouette as dark nebulae.^[136]

GMCs are so large that "local" ones can cover a significant fraction of a constellation; thus they are often referred to by the name of that constellation, e.g. the Orion Molecular Cloud (OMC) or the Taurus Molecular Cloud (TMC). These local GMCs are arrayed in a ring in the neighborhood of the Sun coinciding with the Gould Belt.^[137] The most massive collection of molecular clouds in the galaxy forms an asymmetrical ring around the galactic center at a radius of 120 parsecs; the largest component of this ring is the Sagittarius B2 complex. The Sagittarius region is chemically rich and is often used as an exemplar by astronomers searching for new molecules in interstellar space.^[138]

Def. an interstellar-like cloud apparently surrounding or in orbit around a star is called a circumstellar cloud.

"VY Canis Majoris [a red hypergiant star is] an irregular pulsating variable [that] lies about 5,000 light-years away in the constellation Canis Major."^[139]

"Although VY Can is about half a million times as luminous as the Sun, much of its visible light is absorbed by a large, asymmetric cloud of dust particles that has been ejected from the star in various outbursts over the past 1,000 years or so. The infrared emission from this dust cloud makes VY Can one of the brightest objects in the sky at wavelengths of 5–20 microns."^[139]

"In 2007, a team of astronomers using the 10-meter radio dish on Mount Graham, in Arizona, found that VY Can's extended circumstellar cloud is a prolific molecule-making factory. Among the radio emissions identified were those of hydrogen cyanide (HCN), silicon monoxide (SiO), sodium chloride (NaCl) and a molecule, phosphorus nitride (PN), in which a phosphorus atom and a nitrogen atom are bound together. Phosphorus-bearing molecules are of particular interest to astrobiologists because phosphorus is relatively rare in the universe, yet it is a key ingredient in molecules that are central to life as we know it, including the nuclei acids DNA and RNA and the energy-storage molecule, ATP. "^[139]

"Material ejected by the star is visible in this 2004 image [on the top right] captured by the Hubble Space Telescope's Advanced Camera for Surveys, using polarizing filters."^[139]

For comparison, the second image down on the right is captured using visuals.

"The gas in the clouds of NGC 6559, mainly hydrogen, is the raw material for star formation ... When a region inside this nebula gathers enough matter, it starts to collapse under its own gravity. The center of the cloud grows ever denser and hotter, until thermonuclear fusion begins and a star is born. The hydrogen atoms combine to form helium atoms, releasing energy that makes the star shine. ... In regions where it is very dense, the dust completely blocks the light behind it, as is the case for the dark isolated patches and sinuous lanes to the bottom left-hand side and right-hand side of the image".^[140]

"The Danish 1.54-metre telescope located at ESO’s La Silla Observatory in Chile has captured a striking image of NGC 6559, an object that showcases the anarchy that reigns when stars form inside an interstellar cloud. This region of sky includes glowing red clouds of mostly hydrogen gas, blue regions where starlight is being reflected from tiny particles of dust and also dark regions where the dust is thick and opaque."^[141]

"The two colors of the cloud represent a pair of nebulas. Once the young stars are born, they "energize" the hydrogen surrounding them, ESO officials said. The gas then creates the red wispy cloud — known to astronomers as an "emission nebula" — in the center of the image."^[142]

"These young stars are usually of spectral type O and B, with temperatures between 10 000 and 60 000 K, which radiate huge amounts of high energy ultraviolet light that ionises the hydrogen atoms."^[143]

"The blue section of the photo — representing a "reflection nebula" — shows light from the newly formed stars in the cosmic nursery being reflected in all directions by the particles of dust made of iron, carbon, silicon and other elements in the interstellar cloud."^[142]

NGC 6559 is planetary nebula located at a distance of about 5000 light-years from Earth, in the constellation of Sagittarius.

"NGC 6559 is a cloud of gas and dust located at a distance of about 5000 light-years from Earth, in the constellation of Sagittarius (The Archer). The glowing region is a relatively small object, just a few light-years across, in contrast to the one hundred light-years and more spanned by its famous neighbour, the Lagoon Nebula (Messier 8, eso0936). Although it is usually overlooked in favour of its distinguished companion, NGC 6559 has the leading role in this new picture."^[143]

"The Milky Way fills the background of the image with countless yellowish older stars. Some of them appear fainter and redder because of the dust in NGC 6559."^[143]

"This eye-catching image of star formation was captured by the Danish Faint Object Spectrograph and Camera (DFOSC)".^[143]

"Observations made with the APEX telescope in submillimetre-wavelength light at a wavelength of 870 µm reveal the cold dusty clouds from which stars form in the Carina Nebula. This site of violent star formation, which plays host to some of the highest-mass stars in our galaxy, is an ideal arena in which to study the interactions between these young stars and their parent molecular clouds."^[144]

"The APEX observations, made with its LABOCA camera, are shown here in orange tones, combined with a visible light image from the Curtis Schmidt telescope at the Cerro Tololo Interamerican Observatory. The result is a dramatic, wide-field picture that provides a spectacular view of Carina’s star formation sites. The nebula contains stars equivalent to over 25 000 Suns, and the total mass of gas and dust clouds is that of about 140 000 Suns."^[144]

Most meteoroids that cause meteors are about the size of a pebble.

Def. a particle classification system based on diameter is called the Wentworth scale.

Def. a particle less than 1 micron in diameter is called a colloid.

Def. a particle less than 3.9 microns in diameter is called a clay.

Def. a particle from 3.9 to 62.5 microns in diameter is called a silt.

Def. a particle less than 62.5 microns in diameter is called a mud.

Def. a particle from 62.5 microns to 2 mm in diameter is called a sand.

Def. a particle from 2 to 64 mm in diameter is called a gravel.

Def. a particle from 2 to 4 mm in diameter is called a granule.

Def. a particle from 4 to 64 mm in diameter is called a pebble.

Def. a particle from 64 to 256 mm in diameter is called a cobble.

Def. a particle [or large piece of stone greater than 256 mm in diameter that can theoretically be moved if enough force is applied is called a boulder.

The Comprehensive Suprathermal and Energetic Particle Analyzer (COSTEP) aboard SOHO "detects and classifies very energetic particle populations of solar, interplanetary, and galactic origin."^[145]

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