Contrails - short for "condensation trails" or vapor 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 exists at these high altitudes allows the formation of the trails. Impurities in the jet 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 Their formation can also be triggered by changes in air pressure in wingtip vortices or in the air over the entire wing surface.

Depending on the temperature and humidity at the altitude the contrails form, they may be visible for only a few seconds or minutes, or may persist for hours and spread to be several miles wide, eventually resembling natural cirrus or altocumulus clouds. Persistent contrails are of interest to scientists because they increase the cloudiness of the atmosphere. The resulting cloud forms may resemble cirrus, cirrocumulus, or cirrostratus, and are sometimes called cirrus aviaticus. Persistent spreading contrails are thought by some, without overwhelming scientific proof, to have a significant effect on global climate. Read more

Contrail Shadow X   APOD - April 23, 2024

What created this giant X in the clouds? It was the shadow of contrails illuminated from below. When airplanes fly, humid engine exhaust may form water droplets that might freeze in Earth's cold upper atmosphere. These persistent streams of water and ice scatter light from the Sun above and so appear bright from below. On rare occasions, though, when the Sun is near the horizon, contrails can be lit from below. These contrails cast long shadows upwards, shadows that usually go unseen unless there is a high cloud deck. But that was just the case over Istanbul, Turkiye, earlier this month. Contrails occur all over planet Earth and, generally, warm the Earth when the trap infrared light but cool the Earth when they efficiently reflect sunlight. The image was taken by a surprised photographer in the morning on the way to work.

Image Capture April 15, 2024 - 12:00 pm ET

I took this pic outside my apartment building in Bay Ridge, Brooklyn, New York. What caught my attention was a contrail forming a semi-circle - as contrails generally are parallel or intersecting straight lines. This pic is a combination of the contrails mixed with lens flare and the sun in perfect harmony to bring me a message. This was one week after the famous April 8, 2024 total solar eclipse.

Something appears to Zip by above the obelisk's Pyramidion in the park.

Blue triangle and white object outside my bedroom window

Found: Gaia BH3 the most massive stellar-mass black hole ever spotted in the Milky Way
  Science Alert - April 17, 2024

Black Holes and Simulation Theory

Saturday November 25, 2023

Contrails over the Verrazano Bridge - Pic taken from my terrace

Tuesday August 1, 2023 - Rainbow Contrails

Video: A photographer in Kolkata, India, captured amazing images of rainbow contrails behind an airplane flying overhead

They form when the right combination of air pressure and temperature over the wings creates different sizes of frozen water droplets. The sunlight traveling through them creates the rainbow effect

Tuesday January 4, 2022 - Sunset and Contrails

In these pics the contrails look like shooting stars.

Contrails dissipating

Contrails and Sunsets - April 2021

Contrails Over Bay Ridge and a Full Moon - Tuesday March 30, 2021

Contrails over Bay Ridge - February 2021

Contrails and Sunset over the Verrazano Bridge - March 2016

Contrails over Bay Ridge - Saturday February 20, 2016

Contrails and Birds - February 12, 2012

Chemtrail Conspiracy Theory

The chemtrail conspiracy theory posits the erroneous belief that long-lasting condensation trails are "chemtrails" consisting of chemical or biological agents left in the sky by high-flying aircraft, sprayed for nefarious purposes undisclosed to the general public. Believers in this conspiracy theory say that while normal contrails dissipate relatively quickly, contrails that linger must contain additional substances. Those who subscribe to the theory speculate that the purpose of the chemical release may be solar radiation management, weather modification, psychological manipulation, human population control, biological or chemical warfare, or testing of biological or chemical agents on a population, and that the trails are causing respiratory illnesses and other health problems.

The claim has been dismissed by the scientific community. There is no evidence that purported chemtrails differ from normal water-based contrails routinely left by high-flying aircraft under certain atmospheric conditions. Although proponents have tried to prove that chemical spraying occurs, their analyses have been flawed or based on misconceptions. Because of the persistence of the conspiracy theory and questions about government involvement, scientists and government agencies around the world have repeatedly explained that the supposed chemtrails are in fact normal contrails.

The term chemtrail is a portmanteau of the words chemical and trail, just as contrail is a portmanteau of condensation and trail. Read More ...