Equinox on a Spinning Earth

When does the line between night and day become vertical? Today. Today is an equinox on planet Earth, a time of year when day and night are most nearly equal. At an equinox, the Earth's terminator -- the dividing line between day and night -- becomes vertical and connects the north and south poles. The featured time-lapse video demonstrates this by displaying an entire year on planet Earth in twelve seconds. From geosynchronous orbit, the Meteosat 9 satellite recorded these infrared images of the Earth every day at the same local time. The video started at the September 2010 equinox with the terminator line being vertical. As the Earth revolved around the Sun, the terminator was seen to tilt in a way that provides less daily sunlight to the northern hemisphere, causing winter in the north. As the year progressed, the March 2011 equinox arrived halfway through the video, followed by the terminator tilting the other way, causing winter in the southern hemisphere -- and summer in the north. The captured year ends again with the September equinox, concluding another of billions of trips the Earth has taken -- and will take -- around the Sun.

from NASA https://ift.tt/3CBp332

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The Pencil Nebula Supernova Shock Wave

This supernova shock wave plows through interstellar space at over 500,000 kilometers per hour. Near the middle and moving up in this sharply detailed color composite , thin, bright, braided filaments are actually long ripples in a cosmic sheet of glowing gas seen almost edge-on. Cataloged as NGC 2736 , its elongated appearance suggests its popular name, the Pencil Nebula . The Pencil Nebula is about 5 light-years long and 800 light-years away, but represents only a small part of the Vela supernova remnant . The Vela remnant itself is around 100 light-years in diameter, the expanding debris cloud of a star that was seen to explode about 11,000 years ago. Initially, the shock wave was moving at millions of kilometers per hour but has slowed considerably, sweeping up surrounding interstellar material. In the featured narrow-band, wide field image , red and blue colors track, primarily, the characteristic glows of ionized hydrogen and oxygen atoms , respectively. from NASA https...

This surprising sky has almost everything. First, slanting down from the upper left and far in the distance is the central band of our Milky Way Galaxy . More modestly, slanting down from the upper right and high in Earth's atmosphere is a bright meteor . The dim band of light across the central diagonal is zodiacal light : sunlight reflected from dust in the inner Solar System . The green glow on the far right is aurora high in Earth's atmosphere . The bright zigzagging bright line near the bottom is just a light that was held by the scene-planning astrophotographer . This " almost everything " sky was captured over rocks on Castle Hill , New Zealand late last month. The featured finished frame is a combination of 10 exposures all taken with the same camera and from the same location. But what about the astrophotographer himself? He's pictured too -- can you find him ? from NASA https://ift.tt/8TFhCw3

Lightning and Orion Beyond Uluru

What's happening behind Uluru? A United Nations World Heritage Site , Uluru is an extraordinary 350-meter high mountain in central Australia that rises sharply from nearly flat surroundings. Composed of sandstone , Uluru has slowly formed over the past 300 million years as softer rock eroded away. In the background of the featured image taken in mid-May, a raging thunderstorm is visible. Far behind both Uluru and the thunderstorm is a star-filled sky highlighted by the constellation of Orion. The Uluru region has been a home to humans for over 22,000 years. Local indigenous people have long noted that when the stars that compose the modern constellation of Orion first appear in the night sky, a hot season involving lightning storm s will soon be arriving. from NASA https://ift.tt/3uy2PLM

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