2019 June 28

A Solstice Night in Paris
* Image Credit & Copyright: Loic Michel

Explanation:
The night of June 21 was the shortest night for planet Earth's northern latitudes, so at latitude 48.9 degrees north, Paris was no exception. Still, the City of Light had an exceptionally luminous evening. Its skies were flooded with silvery night shining or noctilucent clouds after the solstice sunset. Hovering at the edge of space, the icy condensations on meteoric dust or volcanic ash are still in full sunlight at the extreme altitudes of the mesophere. Seen at high latitudes in summer months, stunning, wide spread displays of northern noctilucent clouds are now being reported.

https://apod.nasa.gov/apod/ap190628.html

2020 July 4

Meeting in the Mesosphere
* Image Credit & Copyright: Stephane Vetter (TWAN, Nuits sacrees)
http://www.nuitsacrees.fr/

Explanation:
A sensitive video camera on a summit of the Vosges mountains in France captured these surprising fireworks above a distant horizon on 2020 June 26. Generated over intense thunderstorms, this one about 260 kilometers away, the brief and mysterious flashes have come to be known as red sprites. The transient luminous events are caused by electrical breakdown at altitudes of 50 to 100 kilometers. That puts them in the mesophere, the coldest layer of planet Earth's atmosphere. The glow beneath the sprites is from more familiar lighting though, below the storm clouds. But on the right, the video frames have captured another summertime apparition from the mesophere. The silvery veins of light are polar mesospheric clouds. Also known as noctilucent or night shining clouds, the icy clouds still reflect the sunlight when the Sun is below the horizon.

https://apod.nasa.gov/apod/ap200704.html

2020 July 13
Comet NEOWISE Rising over the Adriatic Sea
* Video Credit & Copyright: Paolo Girotti
https://www.instagram.com/astrogyres/

Explanation:
This sight was worth getting out of bed early. Comet C/2020 F3 (NEOWISE) has been rising before dawn during the past week to the delight of northern sky enthusiasts awake that early. Up before sunrise, the featured photographer was able to capture in dramatic fashion one of the few comets visible to the unaided eye this century, an inner-Solar System intruder that might become known as the Great Comet of 2020. The resulting video details Comet NEOWISE from Italy rising over the Adriatic Sea. The time-lapse video combines over 240 images taken over 30 minutes. The comet is seen rising through a foreground of bright and undulating noctilucent clouds, and before a background of distant stars. Comet NEOWISE has remained unexpectedly bright, so far, with its ion and dust tails found to emanate from a nucleus spanning about five kilometers across. Fortunately, starting tonight, northern observers with a clear and dark northwestern horizon should be able to see the sun-reflecting interplanetary snowball just after sunset.

https://apod.nasa.gov/apod/ap200713.html

2021 June 5

The Shining Clouds of Mars
* Image Credit: NASA, JPL-Caltech, MSSS
https://www.nasa.gov/
https://www.jpl.nasa.gov/
https://www.msss.com/

Explanation:
The weathered and layered face of Mount Mercou looms in the foreground of this mosaic from the Curiosity Mars rover's Mast Camera. Made up of 21 individual images the scene was recorded just after sunset on March 19, the 3,063rd martian day of Curiosity's on going exploration of the Red Planet. In the martian twilight high altitude clouds still shine above, reflecting the light from the Sun below the local horizon like the noctilucent clouds of planet Earth. Though water ice clouds drift through the thin martian atmosphere, these wispy clouds are also at extreme altitudes and could be composed of frozen carbon dioxide, crystals of dry ice. Curiosity's Mast Cam has also imaged iridescent or mother of pearl clouds adding subtle colors to the martian sky.

https://apod.nasa.gov/apod/ap210605.html

2020 July 9

Noctilucent Clouds and Comet NEOWISE
* Image Credit & Copyright: Emmanuel Paoly
https://www.flickr.com/photos/184931432@N04/with/50566410986

Explanation:
These silvery blue waves washing over a tree-lined horizon in the eastern French Alps are noctilucent clouds. From high in planet Earth's mesosphere, they reflect sunlight in this predawn skyscape taken on 2020 July 8. This summer, the night-shining clouds were not new to the northern high-latitudes. Comet NEOWISE is though. Also known as C/2020 F3, the comet was discovered in March by the Earth-orbiting Near Earth Object Wide-field Infrared Survey Explorer (NEOWISE) satellite. It's now emerging in morning twilight only just visible to the unaided eye from a clear location above the northeastern horizon.

https://apod.nasa.gov/apod/ap200709.html

2021 June 19

Northern Summer Twilight
* Image Credit & Copyright: Justin Anderson

Explanation:
Nights grow shorter and days grow longer as the summer solstice approaches in the north. Usually seen at high latitudes in summer months, noctilucent or night shining clouds begin to make their appearance. Drifting near the edge of space about 80 kilometers above the Earth's surface, these icy clouds were still reflecting the sunlight on June 14. Though the Sun was below the horizon as seen north of Forrest, Manitoba, Canada, they were caught in a single exposure of a near midnight twilight sky. Multiple exposures of the foreground track the lower altitude flash of fireflies, another fleeting apparition shining in the summer night.

https://apod.nasa.gov/apod/ap210619.html

2021 July 24

The Edge of Space
* Image Credit & Copyright: Ralf Rohner
https://www.instagram.com/skypointer2000/

Explanation:
Where does space begin? For purposes of spaceflight some would say at the Karman line, currently defined as an altitude of 100 kilometers (60 miles). Others might place a line 80 kilometers (50 miles) above Earth's mean sea level. But there is no sharp physical boundary that marks the end of atmosphere and the beginning of space. In fact, the Karman line itself is near the transition between the upper mesosphere and lower thermosphere. Night shining or noctilucent clouds are high-latitude summer apparitions formed at altitudes near the top of the mesosphere, up to 80 kilometers or so, also known as polar mesospheric clouds. Auroral bands of the northern (and southern) lights caused by energetic particles exciting atoms in the thermosphere can extend above 80 kilometers to over 600 kilometers altitude. Taken from a cockpit while flying at an altitude of 10 kilometers (33,000 feet) in the realm of stratospheric aeronautics, this snapshot captures both noctilucent clouds and aurora borealis under a starry sky, looking toward planet Earth's horizon and the edge of space.

https://apod.nasa.gov/apod/ap210724.html

2022 July 12

Noctilucent Clouds over Paris
* Credit & Copyright: Bertrand Kulik
https://www.flickr.com/photos/bertrandkulik/

Explanation:
It's northern noctilucent cloud season. Composed of small ice crystals forming only during specific conditions in the upper atmosphere, noctilucent clouds may become visible at sunset during late summer when illuminated by sunlight from below. Noctilucent clouds are the highest clouds known and now established to be polar mesospheric clouds observed from the ground. Although observed with NASA's AIM satellite since 2007, much about noctilucent clouds remains unknown and so a topic of active research. The featured image shows expansive and rippled noctilucent clouds wafting over Paris, France. This year, several northern locations are already reporting especially vivid displays of noctilucent clouds.

https://apod.nasa.gov/apod/ap220712.html

Timlaps of

Noctilucent Clouds over Florida
* Credit & Copyright: Pascal Fouquet
https://www.pfphotos.art/about/

Annotations for previous post.

Noctilucent Clouds over Florida
* Credit & Copyright: Pascal Fouquet
https://www.pfphotos.art/about/

2024 July 9

Noctilucent Clouds over Florida
* Credit & Copyright: Pascal Fouquet
https://www.pfphotos.art/about/

Explanation:
These clouds are doubly unusual. First, they are rare noctilucent clouds, meaning that they are visible at night -- but only just before sunrise or just after sunset. Second, the source of these noctilucent clouds is actually known. In this rare case, the source of the sunlight-reflecting ice-crystals in the upper atmosphere can be traced back to the launch of a nearby SpaceX rocket about 30 minutes earlier. Known more formally as polar mesospheric clouds, the vertex of these icy wisps happens to converge just in front of a rising crescent Moon. The featured image -- and accompanying video -- were captured over Orlando, Florida, USA about a week ago. The bright spot to the right of the Moon is the planet Jupiter, while the dotted lights above the horizon on the right are from an airplane.

https://apod.nasa.gov/apod/ap240709.html

Noctilucent Clouds explained

Noctilucent Clouds (NLCs) are Earth's highest clouds, that float at the edge of space more than 82 km (50 miles) above the planet's surface. When viewed from space, the same atmospheric phenomenon is referred to as polar mesospheric clouds (PMCs). Noctilucent clouds appear during summer and are probably composed of tiny ice crystals and specks of meteor dust.

Noctilucent or night-shining clouds are rare, high-altitude clouds that glow with a blue silvery hue at dusk or dawn when the Sun shines on them from below the horizon. These ice clouds typically occur near the North and South Poles but are increasingly being reported at mid- and low latitudes. Observing them helps scientists better understand how human activities may affect our atmosphere.

Credits:
Science @ NASA science.nasa.gov
Semen Sh. - NLC 2015.06.23 Timelapse 4K
Noctilucent cloud (серебристые облака) over Bryansk, RU
SciNews

** Note by grobi:
"To upload this video, I converted it and compressed it to a smaller file-size under linux with the free software ffmpeg and the corresponding command:

'ffmpeg -i video_in.mkv -vcodec libx265 -crf 28 video_out.mp4'

Maybe you would like to post a corresponding video on a scientifically related topic, but it is perhaps too big? Then try ffmpeg."

2024 March 12

A Galaxy-Shaped Rocket Exhaust Spiral
* Credit & Copyright: Seung Hye Yang

Explanation:
What's that over the horizon? What may look like a strangely nearby galaxy is actually a normal rocket's exhaust plume -- but unusually backlit. Although the SpaceX Falcon 9 rocket was launched from Vandenberg Space Force Base in California, USA, its burned propellant was visible over a much wider area, with the featured photograph being taken from Akureyri, Iceland. The huge spaceship was lifted off a week ago, and the resulting spectacle was captured soon afterward with a single 10-second smartphone exposure, before it quickly dissipated. Like noctilucent clouds, the plume's brightness is caused by the Twilight Effect, where an object is high enough to be illuminated by the twilight Sun, even when the observer on the ground experiences the darkness of night. The spiral shape is caused by the Falcon rocket reorienting to release satellites in different directions. Stars and faint green and red aurora appear in the background of this extraordinary image.

https://apod.nasa.gov/apod/ap240312.html