Rayleigh scattering is the elastic scattering of light or other electromagnetic radiation by particles much smaller than the wavelength of the light. This effect in our atmosphere causes diffuse sky radiation, which is the reason for the blue color of the sky and the yellow tone of the sun itself.

A portion of the light coming from the sun scatters off molecules and other small particles in the atmosphere. It is this scattered light that gives the sky its brightness and its color. The resulting color, which appears like a pale blue, is actually a weighted average of all the scattered colors, mainly blue and green.

The color of sunlight is intensified when the sun is near the horizon because the volume of air through which sunlight must pass is significantly greater. The Rayleigh scattering effect is therefore increased, removing virtually all blue light from the direct path to the observer. The remaining unscattered light is of a longer wavelength and therefore appears to be orange.

In locations with minimal light pollution, the moonlit night sky is also blue for the same reasons that the sky is blue during the day, as moonlight is reflected sunlight with a slightly lower color temperature due to the brownish color of the moon. The moonlit sky is usually not perceived as blue because at low light levels human vision occurs mainly from rod cells in the eye that do not produce any color perception.


Towering cumulus clouds, also known as cumulus congestus, are characteristic of unstable areas of the atmosphere which are undergoing thermal convection, or the movement of molecules within gases and fluids. They are often characterized by sharp outlines and significant vertical development.

Because cumulus congestus is produced by strong updrafts, it is typically taller than it is wide, and cloud tops can reach 20,000 feet or higher in the tropics. The cloud consists mainly of water droplets. At its top, the water droplets are transformed into ice crystals, but for cumulus congestus the content of ice crystals is small and freezing is in early stages, so cloud top still looks round and puffy.

A pillar of cloud was one of the manifestations of God of the Israelites in the Old Testament. According to Exodus, the pillar of cloud guided the Israelites by day during the Exodus from Egypt. The pillar of cloud is traditionally paired with the the manifestation of God by night as the pillar of fire, which provided light. With these two forms of God leading the way, the Israelites “could travel by day or night”.


Space burial is a burial procedure in which a small sample of the cremated ashes of the deceased are placed in a capsule the size of a tube of lipstick and are launched into space using a rocket. As of 2004, samples of about 150 people have been “buried” in space.

The effort and cost of launching an object into space is very high. Furthermore, the cost is directly related to the payload, i.e. the mass of the object. Therefore various measures are taken to reduce the mass of the burial. The corpse is cremated, reducing the mass of the remains to about 5% of the initial mass. Also, only a small sample of the ashes is included, typically only about 5 grams. The remainder of the ashes can be buried conventionally in the earth or in the sea.

The second factor greatly influencing the cost includes the target location of the payload. Most burials do not actually leave the gravitational field of the earth but only achieve an orbit around earth. The capsules containing the samples of the remains circle the earth, until the upper layers of the Earth’s atmosphere have slowed down the capsules, and they reenter the atmosphere. The capsules burn up upon reentry similar to a shooting star, and the ashes are scattered in the atmosphere. The time between launch and reentry depends on the orbit of the satellite, and can vary widely. The first burial reentered after only 5 years, but other burials are not expected to reenter in less than 250 years.

There are a number of alternative options if a reentry into the earth atmosphere is not desired. All of them are more complex and expensive than a burial in earth orbit. If an object leaves the gravitational field of the earth, it enters the gravitational field of another body in space. The closest object near the earth for that purpose is the moon. Although the moon is technically also in the gravitational field of the earth, it will not hit the earth within any human timeframe. A service is available for space burial on the moon. As of 2005, the only person buried this way is Dr. Eugene Shoemaker, best known for co-discovering the Comet Shoemaker-Levy 9.

The practice of space burials began at the end of the 20th century as the technical difficulties and costs involved in launching an object into space previously made it unfeasible. The first space burial Earthview 01: The Founders Flight was launched on April 21, 1997. An aircraft carried a modified Pegasus rocket containing samples of the remains of 24 people to an altitude of 38,000 ft above the Canary Islands. Famous people buried on this flight were Gene Roddenberry and Timothy Leary.

The second space burial was the burial of a sample of the remains of Dr. Eugene Shoemaker on the moon by the Lunar Prospector probe, launched on January 7, 1999 by a three-stage Athena rocket. The probe containing scientific instruments and the ashes of Dr. Shoemaker impacted the moon near the lunar south pole on 4:52 a.m. Central Daylight Time, July 31, 1999.

Currently, only one company, Space Services Inc., offers space burials. Space Services took over the assets of Celestis, Inc., which launched four flights from 1997 to 2001. As science progresses it is expected that the cost and difficulties of space burials will be reduced, and other companies may enter the market.


A rainbow is an optical and meteorological phenomenon that causes a spectrum of light to appear in the sky when the Sun shines onto droplets of moisture in the Earth’s atmosphere. They take the form of a multicoloured arc, with red on the outer part of the arch and violet on the inner section of the arch.

Rainbows can be observed whenever there are water drops in the air and sunlight shining from behind a person at a low altitude angle. The most spectacular rainbow displays happen when half of the sky is still dark with clouds and the observer is at a spot with clear sky in the direction of the Sun. The result is a luminous rainbow that contrasts with the darkened background.

The rainbow effect is also commonly seen near waterfalls or fountains. The effect can also be artificially created by dispersing water droplets into the air during a sunny day. Rarely, a moonbow, lunar rainbow or night-time rainbow, can be seen on strongly moonlit nights. As human visual perception for colour is poor in low light, moonbows are often perceived to be white.

A rainbow does not actually exist at a particular location in the sky. Its apparent position depends on the observer’s location and the position of the sun. All raindrops refract and reflect the sunlight in the same way, but only the light from some raindrops reaches the observer’s eye. This light is what constitutes the rainbow for that observer. The position of a rainbow in the sky is always in the opposite direction of the Sun with respect to the observer, and the interior is always slightly brighter than the exterior.

The Irish leprechaun’s secret hiding place for his pot of gold is usually said to be at the end of the rainbow. This place is impossible to reach, because the rainbow is an optical effect which depends on the location of the viewer. When walking towards the end of a rainbow, it will move further away.

In Greek mythology, the rainbow was considered to be a path made by the messenger Iris between earth and heaven. In Chinese mythology, the rainbow was a slit in the sky sealed by the goddess Nuwa using stones of five different colours. In Hindu mythology, the rainbow is the bow of Indra, the God of lightning, thunder and rain. After Noah’s Flood, the Bible relates that the rainbow gained meaning as the sign of God’s promise that terrestrial life would never again be destroyed by flood.


The Kessler Syndrome is a scenario, proposed by NASA consultant Donald J. Kessler, in which the volume of space debris in Low Earth orbit is so high that objects in orbit are frequently struck by debris, creating even more debris and a greater risk of further impacts. The implication of this scenario is that the escalating amount of debris in orbit could eventually render space exploration, and even the use of satellites, unfeasible for many generations.

Every satellite, space probe and manned mission has the potential to create space debris. As the number of satellites in orbit grow and old satellites become obsolete, the risk of a cascading Kessler Syndrome becomes greater.

Fortunately, at the most commonly used Low Earth Orbits residual air drag helps keep the zones clear. Altitudes under around 300 miles will be swept clear in a matter of months. Collisions that occur under this altitude are also less of an issue, since the resulting orbits of the fragments inherently have perigee below this altitude.

At altitudes above this level lifetimes are much greater, but drag gradually brings debris down to lower altitudes where it finally re-enters. At very high altitudes this can take millennia.

The Kessler Syndrome is especially insidious because of the “domino effect” and “feedback runaway”. Any impact between two objects of sizable mass spalls off shrapnel debris from the force of collision. Each piece of shrapnel now has the potential to cause further damage, creating even more space debris. With a large enough collision (such as one between a space station and a defunct satellite), the amount of cascading debris could be enough to render Low Earth Orbit essentially impassable.

The Kessler Syndrome presents a unique problem to human space travel. Space debris is very difficult to deal with directly, as the small size and high velocities of most debris would make retrieval and disposal impractically difficult. Given thousands of years, most debris in Low Earth Orbit would eventually succumb to air resistance in the rarefied atmosphere and plunge to the Earth. If magnetically susceptible, the debris could fall in a few decades due to the drag of the Earth’s magnetic field.

To minimize the chances of damage to other vehicles, designers of a new vehicle or satellite are frequently required to demonstrate that it can be safely disposed of at the end of its life, for example by use of a controlled atmospheric reentry system or a boost into a graveyard orbit.


A Fata Morgana is an optical phenomenon which results from a temperature inversion with warmer air above cooler air. The illusions that are created by Fata Morgana show alternations of compressed and stretched image zones.

Fata Morgana can be observed from any altitude within the Earth’s atmosphere including airplanes and mountain tops. For Fata Morgana to be observed, temperature inversions have to be strong enough that the light ray curvature within the inversion is stronger than the curve of the Earth. The rays will bend and create arcs.

In calm weather, the undisturbed interface between warm air over cold dense air near the surface of the ground may act as a refracting lens, producing inverted and erect images. Fata Morgana is the most common in polar regions, especially over large sheets of ice with a uniform low temperature. While in polar regions Fata Morgana is observed on cold days, in deserts and over the oceans and lakes Fata Morgana is observed on hot days.

Sixteen images of the mirage of Farallon Islands, which cannot be seen from the sea level at all under normal conditions because they are located below the horizon, were photographed one hour apart on the same day. The first fourteen frames have elements of Fata Morgana displaying the alternations of compressed and stretched zones. The last two frames were photographed before sunset. The air was cooler while the ocean was a little bit warmer, which made temperature inversion lower. The mirage was still present, but it was not as complex as few hours before sunset, and corresponded not to Fata Morgana, but rather to a different effect called superior mirage display.

Fata Morgana is still playing jokes with unexperienced observers. It is sometimes mistaken for a UFO and can display objects that are located below astronomical horizon as hovering in the sky. Fata Morgana might also magnify these objects and make them look completely unrecognizable.


Tule fog is a thick ground fog that settles in valley areas of California during the late autumn and winter after the first significant rainfall. The official time frame for tule fog to form is from November 1 to March 31, California’s rainy season. This phenomenon is named after the tule grass wetlands of the Central Valley.

Radiation fog is formed by the cooling of land after sunset by thermal radiation in calm conditions with clear sky. The cool ground produces condensation in the nearby air by heat conduction. In perfect calm the fog layer can be less than a meter deep but turbulence can promote a thicker layer. Radiation fogs occur at night, and usually do not last long after sunrise.

In California, tule fog can extend from Bakersfield to Red Bluff. Tule fog occasionally drifts as far west as the San Francisco Bay Area, even drifting westward out the Golden Gate, opposite to the usual course of summertime ocean fog. The nights are longer in the winter months, which creates rapid ground cooling, and thereby a pronounced temperature inversion at a low altitude.

The fog forms when cold mountain air flows downslope into the valley during the night, pooling in the low areas until it fills the valleys. This occurs because most areas in the valley has little or no air drainage below the level of mountains. Because of the density of the cold air in the winter, winds are not able to dislodge the fog and the high pressure of the warmer air above the mountaintops presses down on the cold air trapped in the valley, resulting in a dense fog..

In the California’s Central Valley, Tule fog is a low cloud, usually below 1,000 feet in altitude that can be seen from above by driving up into the foothills of the Sierra Nevada to the east or the Coast Ranges to the west. Above the cold, foggy layer, the air is typically warm, dry and clear. Once tule fog is formed, turbulent air is necessary to break through the temperature inversion layer. Daytime heating sometimes evaporates the fog in some areas, although the air remains chilly and hazy below the inversion. Tule fog usually remains longer in the southern and eastern parts of the Central Valley.

Visibility in tule fog is usually less than an eighth of a mile, but can be less than 10 feet. Visibility can vary rapidly. In only a few feet visibility can go from 10 feet to near zero. Satellite and overhead photos of the San Joaquin Valley may show the fog where agriculture and cities like Sacramento can be seen.

Lack of visibility in tule fog is hazardous enough, but these fog events are often accompanied by drizzle and freezing drizzle. Because of the lack of sunlight penetrating the fog layer, temperatures may struggle to climb above freezing, and episodes of freezing drizzle occasionally accompany tule fog events during winter. Such events can leave an invisible glaze of black ice on roadways, making travel especially treacherous.

Accidents caused by the tule fog are the leading cause of weather-related casualties in California.


The Pineapple Express is a non-technical, shorthand term popular in the news media for a meteorological phenomenon which is characterized by a strong and persistent flow of atmospheric moisture and associated heavy rainfall from the waters adjacent to the Hawaiian Islands and extending to the Pacific coast of North America. The Pineapple Express is driven by a strong, southern branch of the Polar jetstream and is usually marked by the presence of a surface frontal boundary which is typically either slow or stationary, with waves of low pressure traveling along its axis. Each of these low pressure systems brings enhanced rainfall.

The conditions are often created by the Madden-Julian oscillation, an equatorial rainfall pattern which feeds its moisture into this pattern. The combination of moisture laden air, atmospheric dynamics, and orographic enhancement resulting from the passage of this air over the mountain ranges of the West Coast causes some of the most torrential rains to occur in the region. Many Pineapple Express events follow or occur simultaneously with major arctic troughs in the Northwestern United States, often leading to major snowmelt flooding with warm, tropical rains falling on frozen, snow laden ground. Examples of this are the December 1964 Pacific Northwest flood and the Willamette Valley Flood of 1996.

The San Francisco Bay Area is occasionally affected by a Pineapple Express. When it visits, the heavy, persistent rainfall typically causes flooding of local streams as well as urban flooding. In the decades before about 1980, the local term for a Pineapple Express was Hawaiian Storm. During the second week of January, 1952, a series of Hawaiian storms swept into Central California, causing widespread flooding around the Bay Area. The same storms brought a blizzard of heavy, wet snow to the Sierra Nevada Mountains. The greatest flooding in Northern California since the 1800s occurred in 1955 as a result of a series of Hawaiian storms, with the greatest damage in the Sacramento Valley around Yuba City.

A Pineapple Express battered Southern California from January 7 through January 11, 2005. This storm was the biggest to hit Southern California since the El Niño of 1998. The storm caused mud slides and flooding, with one desert location just north of Morongo Valley receiving about 9 inches of rain, and some locations on south and southwest facing mountain slopes receiving spectacular totals. San Marcos Pass, in Santa Barbara County, received 24.57 inches, and Opid’s Camp in the San Gabriel Mountains of Los Angeles County was deluged with 31.61 inches of rain in the five day period.

The Puget Sound region from Olympia, Washington to Vancouver, BC received several inches of rain per day in November 2006 from a series of successive Pineapple Express storms that caused massive flooding in all major regional rivers and mudslides which closed the mountain passes. These storms included heavy winds which are not usually associated with the phenomenon. Regional dams opened their spillways to 100% as they had reached full capacity due to rain and snowmelt. Officials referred to the storm system as the worst in a decade on November 8, 2006. Portions of Oregon were also affected, including over 14 inches in one day at Lee’s Camp in the Coast Range.